This page shows what was measured, who it was measured in, and what that does not settle.
What Sulfamethoxazole does in the body
Urinary, ear, chest, gut and skin infections, and the pneumonia that people with weakened immune systems get
Bacteria have to build folate from raw materials because, unlike your cells, they cannot import it ready-made from food. Building it takes an assembly line, and this tablet contains two drugs that block two consecutive stations on that line: sulfamethoxazole disguises itself as the raw material at the first station, and trimethoprim jams the enzyme at the next one. Blocking one step can be worked around; blocking two consecutive steps is much harder, which is why the label says resistance develops more slowly to the pair than to either alone. Your own cells are untouched because they never run that assembly line — they just eat folate.
What happened in people
Sudden death within 7 days of a prescription, adjusted odds ratio 1.38 against amoxicillin, in older people taking an ACE inhibitor or ARB
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The recorded finding that sits closest to something a person would notice. Written into the record, not signed off, and it carries no population or interval.
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
That the two-drug combination is the right first choice for an uncomplicated urinary tract infection — its own label recommends a single agent instead
Where it acts
Bacterial cytoplasm — the two consecutive enzymes of the folate pathway, one step apart on the same assembly line
Kind of result
Living longer, or avoiding a major event
Supervision
RNAWiki has not recorded a supervision or regulatory status for this substance.
What the registries record it as
The substance registry classes this as chemical.
FDA substance registry · JE42381TNV · read 2026-08-29
Where each sentence above came from
No recorded sentence describes the change this makes in a way that stands on its own. The page opens with what it is taken for instead, and the recorded explanation follows below.
Shown as the opening line on this page.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 149 words.
Words this page uses
Four words worth knowing first
Chosen from what this page shows, with each one explained before the word it depends on.
Comparator
A comparator is whatever the treatment was measured against.
A picture of it, and where the picture fails
It is like the other runner in a race.
Where that stops being true. A race has one winner. A study can show both arms improved.
What people get wrong. Results are read without asking what the other group got. Beating nothing is not beating a treatment.
The control condition against which the experimental intervention is assessed.
Randomisation
Randomisation means chance decides who gets which treatment.
A picture of it, and where the picture fails
It is like a coin toss deciding the groups.
Where that stops being true. A coin toss is fair once. Fairness here comes from doing it for everyone.
What people get wrong. It is thought to make groups identical. It makes them similar on average, including on things nobody measured.
Allocation of participants to arms by a chance process, so that unmeasured factors are balanced in expectation.
Absolute difference
An absolute difference is how many more people in a hundred were affected.
A picture of it, and where the picture fails
It is like counting heads in two rooms of a hundred.
Where that stops being true. Heads are easy to count. Study results carry a margin of error too.
What people get wrong. It is confused with a percentage change, which can look far larger.
The arithmetic difference in event rates between arms.
Confidence interval
A confidence interval is the range the true answer is likely to sit in.
A picture of it, and where the picture fails
It is like a weather forecast giving a range rather than one number.
Where that stops being true. A forecast range covers tomorrow. This one covers what the study could resolve.
What people get wrong. The middle number is read as the answer. A range crossing zero means no change is still possible.
An interval estimate that would contain the true parameter in a stated proportion of repeated studies.
What happened in people◇Read from sources, not yet reviewed
What happened in people
Each card is one study: the exact question it asked, who was in it, and whether it showed what it set out to show.
Clinical cure of a drained uncomplicated skin abscess, assessed 7 to 14 days after the end of treatment
✓ The study showed what it set out to show
Who was studied
Talan DA et al., N Engl J Med 2016;374:823-832 (uncomplicated skin abscess)
80.5% (507/630) against 73.6% (454/617) in the modified intention-to-treat population; difference 6.9 percentage points (95% CI 2.1 to 11.7), p=0.005
Repeated elsewhere
Replicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Invasive infection was identical between arms (2 of 524 against 2 of 533 at 7 to 14 days). The trial was run where MRSA was endemic — 45.3% of wound cultures were MRSA-positive — so the increment attributable to the drug is specific to that setting.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet at 400/80 mg and 800/160 mg (double strength), oral suspension at 200/40 mg per 5 mL, and intravenous infusion — usually taken twice daily
Interval reported. 95% CI 2
Written into the record, not signed off as a reviewed claim.
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
Per protocol 83.5% (182/218) against 85.5% (165/193); difference -2.0% (95% CI -9.7% to 5.7%), p=0.50. Modified intention-to-treat 76.2% against 69.0%; difference 7.3% (95% CI -1.0% to 15.5%), p=0.07
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. The two analysis populations point in opposite directions and neither reaches significance, which is the shape of a result that gets cited in whichever direction the citer prefers.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet at 400/80 mg and 800/160 mg (double strength), oral suspension at 200/40 mg per 5 mL, and intravenous infusion — usually taken twice daily
Interval reported. 95% CI -9
Written into the record, not signed off as a reviewed claim.
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
Occurrence of Pneumocystis pneumonia in immunocompromised patients without HIV infection
✓ The study showed what it set out to show
Who was studied
Green H et al., Mayo Clin Proc 2007;82:1052-1059 (meta-analysis of 12 randomised Pneumocystis prophylaxis trials)
How many people
1245
Study design
Systematic review and random-effects meta-analysis of randomised controlled trials
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
RR 0.09 (95% CI 0.02 to 0.32), a 91% reduction, number needed to treat 15 (95% CI 13 to 20), with no heterogeneity
Repeated elsewhere
Replicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. All-cause mortality did not differ significantly (RR 0.79, 95% CI 0.18 to 3.46) although Pneumocystis-related mortality did (RR 0.17, 95% CI 0.03 to 0.94). Adverse events requiring discontinuation occurred in 3.1% of adults.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet at 400/80 mg and 800/160 mg (double strength), oral suspension at 200/40 mg per 5 mL, and intravenous infusion — usually taken twice daily
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
RNAWiki holds 3 written-up human studies for this substance, each with the question it asked.
How we know it
Each card names the study, the number of people and what the study set out to measure.
What this does not prove
These summaries were written by a person and have not been signed off as reviewed claims.
Why it matters
A study that failed is as informative as one that worked, and both are here.
What we still do not know
No reviewed claim exists, so no exact population, effect size or interval is published yet.
What it changes in the body◇Read from sources, not yet reviewed
The path through the body
From what a person takes to what changes. A solid line is a step measured in people. A dashed line is a step nobody has measured that way.
Start
Sulfamethoxazole
What a person takes: Oral tablet at 400/80 mg and 800/160 mg (double strength), oral suspension at 200/40 mg per 5 mL, and intravenous infusion — usually taken twice daily.
The measurement behind this step
Rapidly absorbed after oral administration, with peak blood levels of each component at one to four hours and steady state reached after three days of twice-daily dosing. Mean serum half-lives are 10 hours for sulfamethoxazole and 8 to 10 hours for trimethoprim, both prolonged in severe renal impairment. Both components distribute into sputum, vaginal fluid and middle ear fluid, cross the placenta and appear in breast milk, and both are excreted primarily by the kidney at urine concentrations considerably higher than blood concentrations.
Getting in
Two drugs, one assembly line
The tablet holds five parts of one drug to one part of another. They block two stations on the same production line, one immediately after the other.
╌╌Measured in animals. A result in animals says what to test next. It does not say what happens in people.
The measurement behind this step
A fixed 5:1 combination at 400/80 mg or 800/160 mg. The label states the pair blocks two consecutive steps in the biosynthesis of nucleic acids and proteins essential to many bacteria, and that in vitro, resistance develops more slowly to the combination than to either component alone.
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
Bacteria build folate starting from a small molecule called PABA. Sulfamethoxazole looks enough like PABA to occupy the machine that consumes it.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Sulfamethoxazole inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid at dihydropteroate synthase. It is a structural analogue, so the inhibition is competitive and can be overcome by raising PABA — which is why pus and necrotic tissue, rich in PABA and thymidine, blunt sulfonamide activity.
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
One step further down the line, trimethoprim locks onto the enzyme that turns the intermediate into the usable form of folate.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
Trimethoprim blocks production of tetrahydrofolic acid from dihydrofolic acid by binding to and reversibly inhibiting dihydrofolate reductase. Its selectivity comes from affinity: it binds the bacterial enzyme orders of magnitude more tightly than the human one, which is why it is not a human antifolate at these doses and methotrexate is.
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
Folate is needed to build one of the four letters of DNA. The organism stops dividing. Your own cells are unaffected because they get folate from food rather than making it.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
Tetrahydrofolate is the one-carbon donor for thymidylate synthase. Blocking it starves the cell of dTMP and halts DNA replication. Human cells lack dihydropteroate synthase entirely and import folate, which is the structural basis of selectivity for the sulfonamide half.
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
Most of both drugs leaves through the kidneys, so urine concentrations are far higher than blood concentrations. That is why it works so well for bladder infections.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Excretion is primarily renal by glomerular filtration and tubular secretion, and the label states urine concentrations of both components are considerably higher than blood concentrations. Of a single oral dose, 84.5% of total sulfonamide and 66.8% of free trimethoprim are recovered in urine over 72 hours. Mean serum half-lives are 10 hours for sulfamethoxazole and 8 to 10 for trimethoprim, both prolonged in renal impairment.
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
The dangerous reactions are immune ones to the sulfonamide, and a potassium rise caused by the trimethoprim acting on the kidney.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
The label records fatal hypersensitivity reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis and aplastic anaemia, and directs discontinuation at the first rash. Separately, trimethoprim blocks the epithelial sodium channel in the distal nephron in a manner resembling amiloride, and the label states that even recommended doses may cause hyperkalaemia in people with renal insufficiency, disordered potassium metabolism, or on other hyperkalaemic drugs.
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 6 steps from taking it to an effect in a person.
How we know it
Each step names the study behind it in the technical detail beside it.
What this does not prove
A change inside the body is a reason to look. It is not a result in a person.
Why it matters
A reader can see exactly where the chain stops being measured in people.
What we still do not know
No reviewed claim binds any of these steps to a named population.
What is missing or unclear◇Read from sources, not yet reviewed
Were people like you studied?
RNAWiki cannot tell whether a study fits you. It can show who was in it, and where the result stops carrying.
Who was studied
People similar to this profile were included.
Adults with urinary infection or bronchitis exacerbation, children with otitis media where the prescriber judges it offers an advantage, travellers with enterotoxigenic diarrhoea, and — the use with the strongest evidence — people who are immunosuppressed and at risk of Pneumocystis pneumonia.
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
Where the result stopped carrying
Adding the drug to cephalexin for non-purulent cellulitis produced no significant improvement in cure
Co-administration with leucovorin during Pneumocystis pneumonia treatment produced treatment failure and excess mortality, and the label now directs avoiding it
The forty-year practice of avoiding all sulfur-containing drugs after a sulfa antibiotic reaction was found to reflect a general allergic predisposition, not chemical cross-reactivity
All-cause mortality did not separate from control in the prophylaxis meta-analysis, and invasive infection did not separate from placebo in the abscess trial
This is a scope explorer, not a diagnosis engine.
It shows who was studied so you can see whether people similar to you were included.
RNAWiki cannot tell whether a study fits you. It can show who was in it.
What it would be like to take◇Read from sources, not yet reviewed
Why it might seem to do nothing
A real effect and a noticed effect are different things. These are the recorded reasons the two come apart.
It was studied in different people
The people in the studies were not much like the reader.
On this record: Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
The evidence may simply be wrong
Small early studies often do not hold up.
On this record: RNAWiki has not yet published a reviewed conclusion for this use.
Other reasons RNAWiki checked and found nothing for (11)
It was studied for a different goal
The studies measured something else entirely. Nothing in this record points to this reason.
A different form was studied
The studied form is not the form on the shelf. Nothing in this record points to this reason.
There was nothing to correct
Where a level is already normal, topping it up may change nothing. Nothing in this record points to this reason.
Something else had to happen too
In the studies it was paired with training, a diet or another treatment. Nothing in this record points to this reason.
The change is too small to feel
A real change can still sit below what a person notices. Nothing in this record points to this reason.
Day-to-day swing hides it
Sleep, food, stress and time of day move most numbers more than this would. Nothing in this record points to this reason.
Not enough time yet
The studies ran longer than the person has waited. Nothing in this record points to this reason.
It was not taken as studied
Missed days change the result, and studies count them. Nothing in this record points to this reason.
Something else changed at the same time
Two changes at once cannot be told apart afterwards. Nothing in this record points to this reason.
The product may not be what it says
Contents of a sold product are not always what the label states. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Given by a clinician
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Oral tablet at 400/80 mg and 800/160 mg (double strength), oral suspension at 200/40 mg per 5 mL, and intravenous infusion — usually taken twice daily
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
RNAWiki has not recorded a supervision or regulatory status for this substance.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
No register row and no identity class settled the question.
No source is stored against this line.
What is in the pack
Rapidly absorbed after oral administration, with peak blood levels of each component at one to four hours and steady state reached after three days of twice-daily dosing. Mean serum half-lives are 10 hours for sulfamethoxazole and 8 to 10 hours for trimethoprim, both prolonged in severe renal impairment.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold. The rest of the recorded wording: Both components distribute into sputum, vaginal fluid and middle ear fluid, cross the placenta and appear in breast milk, and both are excreted primarily by the kidney at urine concentrations considerably higher than blood concentrations.
No source is stored against this line.
Where it is registered
Regulatory records are listed in the technical disclosure at the foot of this page.
# Counted from records
Where this came from
A count of rows RNAWiki holds. It describes our records, not your body.
Register entries are stored per jurisdiction and shown with their dates.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take◇Read from sources, not yet reviewed
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
·Worth asking a clinician aboutWritten into the record from the studies named on this page
Contraindicated in known hypersensitivity to trimethoprim or sulfonamides, in a history of drug-induced immune thrombocytopenia with these drugs, in documented megaloblastic anaemia due to folate deficiency, in infants under two months, and in marked hepatic damage or severe renal insufficiency where renal function cannot be monitored. The label warns that fatalities have occurred from Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anaemia and other blood dyscrasias, and directs discontinuation at the first appearance of rash or any sign of adverse reaction. Also warns of embryofetal toxicity with epidemiological signals for neural tube, cardiovascular, urinary tract and oral cleft defects; of severe and sometimes fatal thrombocytopenia; of hyperkalaemia and of severe symptomatic hyponatraemia; of Clostridioides difficile-associated diarrhoea; and directs adequate fluid intake to prevent crystalluria. Leucovorin must not be co-administered during treatment of Pneumocystis pneumonia.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
Where this came from
Sulfamethoxazole and trimethoprim tablets United States prescribing information — Indications and Usage, Clinical Pharmacology and Microbiology, Contraindica… · a recorded source, not a stored snapshot
Over a long time. No completed tested study window is recorded, so long-term effects are not established by the registry record.
Groups the studies covered thinly. Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What is missing or unclear◇Read from sources, not yet reviewed
Does the exact form matter?
Evidence belongs to the exact thing that was tested. A different salt, a different mixture or a different preparation is a different question.
The form that was studied
Oral tablet at 400/80 mg and 800/160 mg (double strength), oral suspension at 200/40 mg per 5 mL, and intravenous infusion — usually taken twice daily
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form used in the studies cited on this page.
No source is stored against this line.
What is sold
Mean serum half-lives are 10 hours for sulfamethoxazole and 8 to 10 hours for trimethoprim, both prolonged in severe renal impairment.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on which forms are sold. The rest of the recorded wording: Both components distribute into sputum, vaginal fluid and middle ear fluid, cross the placenta and appear in breast milk, and both are excreted primarily by the kidney at urine concentrations considerably higher than blood concentrations.
No source is stored against this line.
What is recorded as being sold
1 published label names it as an active ingredient. None of them describes this substance alone, so no label text on this page can be attributed to it rather than to a combination.
US prescribing information · ede74118-32c5-4f52-9823-509538e674c8 · read 2026-08-29
Those labels are classed as human prescription drug.
US prescribing information · ede74118-32c5-4f52-9823-509538e674c8 · read 2026-08-29
Sulfamethox-TMP DS is oral at HOW SUPPLIED Sulfamethoxazole and Trimethoprim Tablets, USP are supplied as follows: Sulfamethoxazole and Trimethoprim DS (double strength) Tablets USP, 800 mg, are supplied as white, oval, bisected tablets debossed “IP…, recorded as fda label in effect 2022-10-09 in the United States.
US prescribing information · ede74118-32c5-4f52-9823-509538e674c8 · read 2026-08-30
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
What it would be like to take◇Read from sources, not yet reviewed
What you could measure
This one is decided with a clinician, so this section holds questions to ask rather than a plan to run.
RNAWiki could not confidently classify this substance, so no self-experiment plan is offered.
Questions worth asking
Which of the trials of Sulfamethoxazole studied people like me?
What was measured, and for how long?
Was the result a laboratory value or a health outcome?
What would we watch for, and when would we stop?
Tracking can show whether something changed for you. It cannot show what caused it.
RNAWiki records evidence. It does not say whether this substance is right for you.
What is missing or unclear◇Read from sources, not yet reviewed
Claims that go past the evidence
Things said about this substance that sound reasonable, and the exact step that is missing between the evidence and the claim.
✗Goes past the evidence
That the two-drug combination is the right first choice for an uncomplicated urinary tract infection — its own label recommends a single agent instead
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That covering MRSA improves outcomes in non-purulent cellulitis; a 500-patient double-blind trial found a difference of -2.0% (p=0.50)
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That preventing Pneumocystis pneumonia lowers all-cause mortality; the meta-analysis found RR 0.79 with a confidence interval from 0.18 to 3.46
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That relieving a sore throat means the streptococcal infection has been treated — the label states sulfonamides will not eradicate the organism and will not prevent rheumatic fever
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
What is missing or unclear◇Read from sources, not yet reviewed
What nobody knows yet
Open questions, each with why it is open and what would close it.
Missing populations
Which groups were under-represented in the studies has not been recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing long-term data
No completed tested study window is recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
No reviewed conclusion
RNAWiki has not yet published a reviewed conclusion for this use.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing interaction studies
No interaction was found in the registers checked. Not finding one is not the same as showing there is none.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Formulation uncertainty
Several salts, forms or products of Sulfamethoxazole are recorded. Results from one form may not transfer to another.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Mechanism not reviewed
No reviewed mechanism story exists for this substance.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
What happened in people◇Read from sources, not yet reviewed
Check any of this yourself
Every line above traced back to the study it came from. This is the technical layer, and the vocabulary changes here.
Every line above can be traced to the study named beside it. Follow the link and read it.
A 91% reduction in Pneumocystis pneumonia, with mortality that did not follow
In plain words
Across twelve randomised trials in people with weakened immune systems, this drug cut Pneumocystis pneumonia by ninety-one per cent — one case prevented for every fifteen people treated. Deaths from that pneumonia fell too. Deaths from all causes did not change significantly.
What was measured
Occurrence of Pneumocystis pneumonia, Pneumocystis-related mortality and all-cause mortality across 12 randomised trials
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A systematic review and meta-analysis of 12 randomised trials in 1,245 immunocompromised patients without HIV — autologous bone marrow or solid organ transplant recipients and people with haematological cancer, half of them children — found a 91% reduction in Pneumocystis pneumonia with trimethoprim-sulfamethoxazole (RR 0.09, 95% CI 0.02 to 0.32), number needed to treat 15 (95% CI 13 to 20), with no heterogeneity. Pneumocystis-related mortality fell significantly (RR 0.17, 95% CI 0.03 to 0.94). All-cause mortality did not differ significantly (RR 0.79, 95% CI 0.18 to 3.46). Adverse events requiring discontinuation occurred in 3.1% of adults and none of the children, all reversible. The authors conclude prophylaxis is warranted when the risk of Pneumocystis pneumonia exceeds 3.5% in adults — a threshold, not a blanket recommendation, and it exists because the benefit is measured against a harm.
Written into the record, not signed off as a reviewed claim
After draining an abscess, the antibiotic added seven percentage points
In plain words
A 1,247-patient trial gave people whose skin abscess had been drained either this drug or a placebo. Cure was 80.5% with the drug and 73.6% with placebo. Most of the benefit was in stopping new infections elsewhere and in household members.
What was measured
Clinical cure of a drained uncomplicated skin abscess 7 to 14 days after treatment, against placebo
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A randomised trial at five United States emergency departments enrolled outpatients over 12 with an uncomplicated abscess treated by drainage; 45.3% had wound cultures positive for MRSA. In the modified intention-to-treat population, clinical cure occurred in 507 of 630 (80.5%) on trimethoprim-sulfamethoxazole against 454 of 617 (73.6%) on placebo, a difference of 6.9 percentage points (95% CI 2.1 to 11.7, p=0.005). Per protocol, 92.9% against 85.7% (difference 7.2 points, 95% CI 3.2 to 11.2, p<0.001). Secondary outcomes favoured the drug: subsequent surgical drainage 3.4% against 8.6%, new-site skin infection 3.1% against 10.3%, infection in a household member 1.7% against 4.1%. Invasive infection was identical — 2 of 524 against 2 of 533 at 7 to 14 days. The honest reading is that drainage does most of the work, the antibiotic adds a modest increment to cure and a larger one to preventing spread, and it changes nothing about the rare serious outcome.
Written into the record, not signed off as a reviewed claim
Adding it to cephalexin for cellulitis did nothing
In plain words
For cellulitis without an abscess, doctors often add this drug to cover MRSA. A 500-patient double-blind trial found adding it made no difference: 83.5% cured with it, 85.5% without.
What was measured
Clinical cure of non-purulent uncomplicated cellulitis with and without added MRSA coverage
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
A multicentre double-blind randomised superiority trial in five United States emergency departments enrolled 500 outpatients over 12 with cellulitis and no wound, purulent drainage or abscess — ultrasound was performed on every participant at enrolment to exclude an abscess. Participants received cephalexin plus trimethoprim-sulfamethoxazole or cephalexin plus placebo for seven days. In the pre-specified per-protocol population, clinical cure occurred in 182 of 218 (83.5%) with the combination against 165 of 193 (85.5%) with cephalexin alone, a difference of -2.0% (95% CI -9.7% to 5.7%, p=0.50). In the modified intention-to-treat population the difference was 7.3% (95% CI -1.0% to 15.5%, p=0.07), also not significant. Adverse event rates did not differ. The trial tested a specific and widespread inference — that because MRSA is common in skin infection, a regimen covering MRSA must do better in non-purulent cellulitis — and did not support it.
Written into the record, not signed off as a reviewed claim
The label recommends a single agent for the infection it is most used for
In plain words
For a first uncomplicated bladder infection, the prescribing information says to use one effective antibiotic rather than this two-drug combination. That is the commonest reason it is prescribed.
What was measured
That the two-drug combination is the appropriate first choice for an uncomplicated urinary tract infection, otitis media or a bronchitis exacerbation — an inference the label declines to make and, for uncomplicated urinary infection, explicitly reverses
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Indications and Usage section, under Urinary Tract Infections, reads: "It is recommended that initial episodes of uncomplicated urinary tract infections be treated with a single effective antibacterial agent rather than the combination." The same section attaches similar qualifications elsewhere: acute otitis media is indicated only "when in the judgment of the physician sulfamethoxazole and trimethoprim tablets offer some advantage over the use of other antimicrobial agents", the product is explicitly "not indicated for prophylactic or prolonged administration in otitis media at any age", and acute exacerbation of chronic bronchitis is indicated only when the prescriber deems the combination "could offer some advantage over the use of a single antimicrobial agent". Three of the drug’s licensed indications therefore carry a written instruction to justify choosing it over something simpler, and those three account for most of its use.
Source
Sulfamethoxazole and trimethoprim tablets United States prescribing information, Indications and Usage (NDA 017377)
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
contested
Review state
Written into the record, not signed off as a reviewed claim
The sulfa allergy that was never a cross-reaction
In plain words
For decades, people with a sulfa antibiotic allergy were kept away from unrelated sulfur-containing drugs — some diuretics, some diabetes tablets. A 20,000-patient study found the extra risk was not cross-reactivity at all. It was that allergic people are allergic to more things.
What was measured
Allergic reaction within 30 days of a sulfonamide non-antibiotic, with a penicillin comparator arm
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A retrospective cohort study in the United Kingdom General Practice Research Database examined allergic reactions within 30 days of receiving a sulfonamide non-antibiotic. Of 969 patients with a prior allergic reaction to a sulfonamide antibiotic, 96 (9.9%) reacted to a subsequent sulfonamide non-antibiotic, against 315 of 19,257 (1.6%) with no prior reaction — adjusted odds ratio 2.8 (95% CI 2.1 to 3.7). The result that broke the cross-reactivity theory is the control: among the same patients with a prior sulfonamide-antibiotic reaction, the risk of reacting to a penicillin was higher still (adjusted OR 3.9, 95% CI 3.5 to 4.3), and lower after a sulfonamide non-antibiotic than after a penicillin (adjusted OR 0.7, 95% CI 0.5 to 0.9). Penicillin shares no sulfonamide chemistry whatever. The authors conclude the association reflects a predisposition to allergic reactions rather than cross-reactivity with sulfonamide-based drugs. The label still contraindicates the drug in known hypersensitivity to sulfonamides, which is correct and is a different statement.
Written into the record, not signed off as a reviewed claim
Sudden death in older people already on a blood pressure drug
In plain words
In Ontario, older people taking an ACE inhibitor or an ARB were about 40% more likely to die suddenly in the week after this antibiotic than after amoxicillin. The suspected cause is a potassium rise nobody measured.
What was measured
Sudden death within 7 and 14 days of an outpatient antibiotic prescription, against an amoxicillin comparator
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
A population-based nested case-control study of Ontario residents aged 66 or over treated with an ACE inhibitor or angiotensin receptor blocker identified 39,879 sudden deaths, of which 1,027 occurred within seven days of an outpatient antibiotic prescription, matched to 3,733 controls. Relative to amoxicillin, co-trimoxazole carried an adjusted odds ratio for sudden death of 1.38 (95% CI 1.09 to 1.76) at seven days and 1.54 (1.29 to 1.84) at fourteen days — approximately three sudden deaths within fourteen days per 1,000 prescriptions. Ciprofloxacin, a known cause of QT prolongation, was also associated (adjusted OR 1.29, 1.03 to 1.62); nitrofurantoin and norfloxacin were not. The authors attribute the finding to unrecognised severe hyperkalaemia. The label already warns that recommended doses may cause hyperkalaemia when trimethoprim is given with drugs known to induce it, and directs close monitoring of serum potassium; the study measures what happens when that instruction is not followed in ordinary practice.
Written into the record, not signed off as a reviewed claim
The rescue drug that increased mortality
In plain words
Leucovorin is given to protect people from folate-blocking drugs. Adding it to this drug during treatment of Pneumocystis pneumonia caused treatment failure and more deaths, and the label now says not to.
What was measured
Treatment failure and mortality with concomitant leucovorin during treatment of Pneumocystis pneumonia
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The Warnings section states, under Adjunctive Treatment with Leucovorin for Pneumocystis jiroveci Pneumonia: "Treatment failure and excess mortality were observed when trimethoprim-sulfamethoxazole was used concomitantly with leucovorin for the treatment of Pneumocystis jiroveci pneumonia", and the Precautions section directs that co-administration be avoided. The reasoning that led to the practice was mechanically impeccable — this drug blocks folate metabolism, leucovorin is reduced folate, therefore leucovorin should relieve the haematological toxicity without touching the antimicrobial effect, because Pneumocystis cannot take up preformed folate. The clinical result went the other way. It is one of the cleanest examples in the pharmacopoeia of a mechanism argument that survived scrutiny and still produced the wrong answer in patients.
Source
Sulfamethoxazole and trimethoprim tablets United States prescribing information, Warnings and Precautions (NDA 017377)
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
caution
Review state
Written into the record, not signed off as a reviewed claim
It will not prevent rheumatic fever, and the label says so directly
In plain words
Sulfonamides do not clear strep throat. The label states they will not eradicate the organism and therefore will not prevent rheumatic fever — one of the few places a drug label rules out a use in a single sentence.
What was measured
That a broadly active antibacterial which improves a sore throat has treated the streptococcal infection behind it — an inference the label reverses in one sentence
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Under Warnings, Streptococcal Infections and Rheumatic Fever: "The sulfonamides should not be used for treatment of group A β-hemolytic streptococcal infections. In an established infection, they will not eradicate the streptococcus and, therefore, will not prevent sequelae such as rheumatic fever." The distinction matters because sulfonamides do suppress streptococcal growth well enough to have been used for rheumatic fever prophylaxis in people who already had the disease — a secondary prevention use — while failing at eradication in an active pharyngitis. A drug that improves symptoms without clearing the organism is exactly the shape of failure that produces a confident wrong inference, and this label closes it explicitly.
Source
Sulfamethoxazole and trimethoprim tablets United States prescribing information, Warnings (NDA 017377)
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
caution
Review state
Written into the record, not signed off as a reviewed claim
Where else this substance is registered
FDA substance identifier (UNII)
JE42381TNV
CAS registry number
723-46-6
PubChem compound
5329
ChEMBL
CHEMBL443
ChEBI
9332
WHO international nonproprietary name list entry
1386
RxNorm concept
10180
EMA substance identifier
100000092618
European Chemicals Agency number
211-963-3
DrugBank
DB01015
Checks this page had to pass
✓ Passed
Identity resolved
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✓ Passed
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no quarantine open
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Every public sentence names a source
The opening statement carries the origin: Written into the record, not signed off.
✗ Not passed
Trial roles classified for highlighted evidence
No registered study is classified as testing this substance.
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No internal keys in reader text
enforced by the copy-contract test over the rendered page
✗ Not passed
Safety mode resolved
No register row and no identity class settled the question.
✓ Passed
Canonical metadata present
slug and display name present
What is missing or unclear◇Read from sources, not yet reviewed
How this medicine reached us
Kept near the foot of the page. A historical event moves up only when it changes something about this substance today.
Withdrawn in United States, 2025, for "Microbial contamination of non-sterile products: tablets may exhibit black spots due to microbial contamination." (openFDA drug enforcement Class I recall)
What is missing or unclear◇Read from sources, not yet reviewed
What to learn next
Ordered by what would most change how you read this page, starting with what is easiest to misunderstand.
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What is not here
7 questions this page could not answer
These sections were prepared and left out because there was nothing to put in them. They are listed rather than hidden, so the gaps in this record are visible.
What was measured, goal by goal — found nothing in the sources checked.
How close this is to real life — found nothing in the sources checked.
Felt, measured, or meaningful — found nothing in the sources checked.
How long anything takes — found nothing in the sources checked.
What it may clash with — found nothing in the sources checked.
Other ways to the same goal — found nothing in the sources checked.
What changed on this page — found nothing in the sources checked.
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The full record, for auditing
Everything above is built from what is below. This layer keeps the technical vocabulary, record identifiers and every stored row, so a reader who wants to check the page can.
The older medicine-wide conclusion held in this record
Written for a clinical reader, and about the medicine as a whole rather than about one indication, population and set of trials. RNAWiki does not treat it as a programme conclusion and no reviewer has signed it off in that form. It is here word for word because it is what the record holds.
Two folate-pathway blockers one step apart, which cut Pneumocystis pneumonia by 91% in a meta-analysis of 12 randomised trials in 1,245 non-HIV immunocompromised patients (RR 0.09, 95% CI 0.02 to 0.32, number needed to treat 15) — and whose own FDA label recommends a single agent rather than this combination for a first uncomplicated urinary tract infection, the thing it is most often prescribed for.
Recorded evidence blocks (7)
Q1
129 registered trials of Sulfamethoxazole — at which phases?
Registered studies posting no result
102 of 129
129 registered studies of Sulfamethoxazole: 41 phase2, 35 phase3, 26 phase4, 20 na, 14 phase1, 7 na or unstated, 1 early phase1. CLINICALTRIALS_SNAPSHOT · 2026-09-01
56 with a PubMed record
Show the evidence
phase2
41
phase3
35
phase4
26
na
20
phase1
14
na or unstated
7
10 more recorded rows
early phase1
1
completed
75
recruiting
17
terminated
13
unknown
11
withdrawn
5
not yet recruiting
4
active not recruiting
2
enrolling by invitation
1
no longer available
1
recorded 2026-09-01 · last checked 2026-09-04
Q2
17 of Sulfamethoxazole's trials stopped: safety, futility/efficacy, accrual/recruitment, funding/business, other?
safety (2), futility/efficacy (1), accrual/recruitment (8), funding/business (1) and other (5): Sulfamethoxazole's stop wording, clustered. CLINICALTRIALS_SNAPSHOT · 2026-09-01
"Effective August 13, 2004: Unanticipated high incidence of post-transplant lymphoproliferative disorder"; 17 of 129 registered studies
Show the evidence
Trial
NCT00023244
terminated; "Effective August 13, 2004: Unanticipated high incidence of post-transplant lymphoproliferative disorder"
NCT00080119
terminated; "Data Safety Monitoring Board (DSMB) recommended stopping study due to futility"
NCT00302341
terminated; "FDA Clinical Hold as of 12/21/07 due to safety concerns"
NCT00752375
withdrawn; "No participants"
NCT00789464
withdrawn; "Withdrawn by PI"
NCT00867789
terminated; "Slow enrollment due to subjects not meeting inclusion/exclusion criteria"
11 further recorded trials
NCT00900510
withdrawn; "Recruitment of this population in the hospital setting not practical."
NCT01101412
withdrawn; "Study was not opened."
NCT01349192
terminated; "Interim review showed a statistically significant treatment effect and the DMC recommended that the study be stopped with ongoing follow-up of enrolled subjects"
NCT01756924
terminated; "This study has been terminated; alternative study designs are being considered. Fusidic acid remains available under an Expanded Access Protocol."
NCT02099240
terminated; "Not enough patient enrollment and lack of staffing"
NCT02168816
terminated; "The study was stopped for feasibility (i.e., low recruitment)"
NCT03173053
terminated; "Results interim-analysis"
NCT03508921
terminated; "Early termination due to recruitment and follow-up challenges during the pandemic"
NCT05418777
terminated; "lack of enrollment"
NCT05823467
terminated; "Logistical Issues"
NCT06207786
withdrawn; "Lack of resources to support the trial"
recorded 2026-09-01 · last checked 2026-09-04
Q3
Human studies of Sulfamethoxazole used Sulfamethoxazole 800mg + Trimethoprim 160mg = Bactrim F. — over how long?
Human studies of Sulfamethoxazole used "Sulfamethoxazole 800mg + Trimethoprim 160mg = Bactrim F." ClinicalTrials.gov · 2026-09-01
2 recorded entries; human; also "trimethoprim/sulfamethoxazole 160 mg/800 mg"
Show the evidence
human
NCT01449877
Sulfamethoxazole 800mg + Trimethoprim 160mg = Bactrim F.
NCT01808755
trimethoprim/sulfamethoxazole 160 mg/800 mg
recorded 2026-09-01 · last checked 2026-09-04
Q4
Which running trial of Sulfamethoxazole could settle lifespan?
NCT07202052 measures Event-free survival (EFS), reading out 2027-03-31.
4 open trials; n 900; "Role of Antibiotic Therapy or Immunoglobulin On iNfections in hAematoLogy Platform Trial (RATIONAL-PT)"
Show the evidence
Trial
NCT07202052
"Role of Antibiotic Therapy or Immunoglobulin On iNfections in hAematoLogy Platform Trial (RATIONAL-PT)"; n 900; "Event-free survival (EFS)"; 2027-03-31
NCT07202078
"Role of Antibiotic Therapy or Immunoglobulin On iNfections in hAematoLogy: Starting Immunoglobulin (Start Ig)"; n 900; "Event-free survival (EFS)."; 2027-03-31
NCT07202091
"Role of Antibiotic Therapy or Immunoglobulin On iNfections in hAematoLogy Immunoglobulin Stopping or Extension (Stop Ig)"; n 900; "Event-free survival (EFS)."; 2027-03-31
NCT05678621
"Role of Antibiotic Therapy or Immunoglobulin On iNfections in hAematoLogy: Immunoglobulin Stopping or Extension"; n 300; "Event-free survival (EFS), defined as time from randomisation until occurrence of a Grade 3 or higher infection (as defined by CTCAE Version 5), or death from any cause."; 2027-04
Q5
Which 44 trials of Sulfamethoxazole posted no result?
Posted no result
44 of 44 completed trials
Registrations
NCT00000732, NCT00000734, NCT00000727, NCT00000715, NCT00001013 and NCT00001014, and 38 more
Completion dates
oldest 1990-05; newest 2021-11-14
Show the evidence
Trial
NCT00000732
1990-05
NCT00000734
1990-05
NCT00000727
1991-08
NCT00000715
1991-09
NCT00001013
1991-09
NCT00001014
1991-09
14 further recorded trials
NCT00000991
1994-04
NCT00000640
1994-09
NCT00000816
1996-09
NCT00000748
1996-11
NCT00000826
1999-05
NCT00168532
2001-10
NCT00000811
2001-11
NCT00791505
2005-06
NCT00002524
2005-10
NCT00382343
2007-03
NCT00126698
2007-04
NCT00324922
2007-05-01
NCT00004216
2008-01
NCT01049438
2009-09
Q6
At the median, Sulfamethoxazole's trials enrolled 130 people — anything larger?
Median enrolment
130
Largest enrolment
2800
Registered trials counted
125
Q7
What do 9483 spontaneous reports say about Sulfamethoxazole — and not say?
These are reports people sent to a regulator. They do not show the medicine caused the reaction. Nobody counted how many people took the medicine and reported nothing. The same event can be reported more than once, and many reports are incomplete. News coverage, lawsuits and new warnings change how often people report. A count is not a rate and not a risk.
Sulfamethoxazole appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 9483 reaction mentions were counted: drug hypersensitivity 1690; pyrexia 1360; rash 1340; pruritus 938. FAERS via Open Targets · CHEMBL443 · 2026-06-24
Show the evidence
drug hypersensitivity
1690
pyrexia
1360
rash
1340
pruritus
938
hypersensitivity
765
dyspnoea
747
4 more recorded rows
arthralgia
702
pain
653
peripheral swelling
653
joint swelling
635
recorded 2026-06-24 · last checked 2026-09-04
Where it is registered
Where it’s registered
Withdrawn in United States, 2025, for "Microbial contamination of non-sterile products: tablets may exhibit black spots due to microbial contamination." (openFDA drug enforcement Class I recall)
Gantanol, Gantanol-ds, Sinomin, Sulfamethoxazole component of azo gantanol, Sulfamethoxazole component of bactrim, Sulfamethoxazole component of bactrim ds, Sulfamethoxazole component of bactrim pediatric, Sulfamethoxazole component of cotrim, Sulfamethoxazole component of cotrim d.s., Sulfamethoxazole component of co-trimethoxazole, Sulfamethoxazole component of septra, Sulfamethoxazole component of sulfamethoprim
ChEMBL 37 — CC BY-SA 3.0 Unported · ChEMBL ATC CC BY-SA · ClinicalTrials.gov — US Government work · Open Targets 26.06 — CC0 · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA enforcement — US Government work
✗ required summary fields resolved: 4 required field(s) not terminal: Why people use it, Best-supported result, Biggest unanswered question, Human evidence
✓ public claims reviewed: 0 reviewed claim(s); drafts are never rendered
✓ source coverage passed: 6 source rows
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