This page shows what was measured, who it was measured in, and what that does not settle.
What Phenoxymethylpenicillin does in the body
A dividing bacterium keeps making new wall material it can never cross-link, and it bursts.
A bacterium is under pressure from the inside, and the only thing holding it together is a mesh wall it has to keep re-stitching while it grows. Penicillin V looks enough like the end of the peptide chain those stitching enzymes normally grab that they grab it instead — and then cannot let go. Human cells have no such wall, which is why the drug is nearly harmless to them, and why the dangerous reactions to it are immune reactions rather than toxic ones.
Why people take it. Strep throat and other streptococcal infections, and long-term prevention of rheumatic fever coming back
What happened in people
Acute rheumatic fever within two months reduced with a Peto odds ratio of 0.36 (95% CI 0.26 to 0.50) across 18 trials and 12,249 participants
✎ 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.
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · a recorded source, not a stored snapshot
That the ten-day minimum in the label is a trial-established duration rather than eradication-based reasoning from the 1950s
Where it acts
The bacterial cell wall — the transpeptidase active site, in an organism that is actively dividing
Kind of result
The kind of result is not recorded
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 · Z61I075U2W · read 2026-08-29
Where each sentence above came from
A person wrote this explanation into the record, with the studies named in the path below.
The recorded use, written for a reader without medical training. Not signed off.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 141 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.
Sore throat at day three and at one week, with acute rheumatic fever and suppurative complications as secondary outcomes
✓ The study showed what it set out to show
Who was studied
Spinks A et al., Cochrane Database Syst Rev 2021;12:CD000023 (29 randomised trials of antibiotics against placebo or no treatment for sore throat)
How many people
15337
Study design
Systematic review and meta-analysis of randomised and quasi-randomised trials
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Sore throat at day three RR 0.70 (95% CI 0.60 to 0.80), number needed to treat below 6; at one week RR 0.50 (0.34 to 0.75), number needed to treat 18. Acute rheumatic fever within two months Peto OR 0.36 (0.26 to 0.50; 18 studies, 12,249 participants)
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. Harms from antibiotics were poorly or inconsistently reported and could not be quantified in the review. Eighty-two per cent of control participants were symptom-free by one week. Fever at day three was not significantly reduced (RR 0.75, 0.53 to 1.07, high certainty). Most included studies date from the 1950s, when rheumatic fever was far commoner, and few distinguished bacterial from viral aetiology.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet at 250 mg (400,000 units) and 500 mg (800,000 units) of penicillin V potassium, and an oral solution at 125 and 250 mg per 5 mL — typically taken three or four times daily
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · a recorded source, not a stored snapshot
Clinical cure five to seven days after the end of treatment in group A streptococcal pharyngotonsillitis, penicillin V 800 mg four times daily for 5 days against 1,000 mg three times daily for 10 days
✓ The study showed what it set out to show
Who was studied
Skoog Ståhlgren G et al., BMJ 2019;367:l5337 (5-day against 10-day penicillin V)
How many people
433
Study design
Open-label, randomised, controlled non-inferiority trial in 17 primary care centres
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Per protocol clinical cure 89.6% (181/202) against 93.3% (182/195); 95% CI -9.7 to 2.2, within the pre-specified 10 percentage point non-inferiority margin
Repeated elsewhere
Unreplicated
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. Bacteriological eradication was lower on the five-day regimen: 80.4% (156/194) against 90.7% (165/182). Since eradication rather than symptom resolution is the mechanism by which rheumatic fever is prevented, the two endpoints do not support the same conclusion. Relapses were 8 against 7 and complications 0 against 4; the ten-day group had a higher incidence and longer duration of adverse events.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet at 250 mg (400,000 units) and 500 mg (800,000 units) of penicillin V potassium, and an oral solution at 125 and 250 mg per 5 mL — typically taken three or four times daily
Interval reported. 95% CI -9
Written into the record, not signed off as a reviewed claim.
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · a recorded source, not a stored snapshot
Echocardiographic progression of latent rheumatic heart disease at 2 years in Ugandan children and adolescents aged 5 to 17
✓ The study showed what it set out to show
Who was studied
GOAL trial (Beaton A et al., N Engl J Med 2022;386:230-240)
How many people
818
Study design
Randomised, controlled, open-label trial with blinded outcome adjudication
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
3 of 399 (0.8%) on four-weekly benzathine penicillin G against 33 of 401 (8.2%) with no prophylaxis; risk difference -7.5 percentage points (95% CI -10.2 to -4.7), p<0.001
Repeated elsewhere
Unreplicated
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. Two participants had serious adverse events attributable to prophylaxis, including one mild anaphylactic reaction, representing under 0.1% of all doses administered. The trial used the injected depot formulation, not oral penicillin V, and enrolled people who already had detectable valve damage.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet at 250 mg (400,000 units) and 500 mg (800,000 units) of penicillin V potassium, and an oral solution at 125 and 250 mg per 5 mL — typically taken three or four times daily
Interval reported. 95% CI -10
Written into the record, not signed off as a reviewed claim.
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · 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
Phenoxymethylpenicillin
What a person takes: Oral tablet at 250 mg (400,000 units) and 500 mg (800,000 units) of penicillin V potassium, and an oral solution at 125 and 250 mg per 5 mL — typically taken three or four times daily.
The measurement behind this step
The potassium salt resists gastric acid inactivation, which is the property that makes an oral penicillin possible; average blood levels are two to five times those after the same oral dose of penicillin G with much less individual variation. It may be given with meals, though levels are slightly higher fasting. Only about 25% of an oral dose is absorbed, roughly 80% of the absorbed drug is protein bound, and elimination is renal and as rapid as absorption in normal kidney function. Excretion is considerably delayed in neonates, young infants and renal impairment.
Getting in
It survives the stomach, which penicillin G does not
The whole reason this version exists is a chemical side group that resists stomach acid, so it can be swallowed rather than injected.
╌╌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
Penicillin V is the phenoxymethyl analogue of penicillin G. The label states the potassium salt has the distinct advantage of resistance to inactivation by gastric acid, and that average blood levels are two to five times higher than after the same oral dose of penicillin G, with much less individual variation. It may be taken with meals, though levels are slightly higher fasting.
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · a recorded source, not a stored snapshot
Most of a swallowed dose never reaches the bloodstream, and what does is cleared almost immediately. Hence four doses a day.
╌╌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
Recovery from urine indicates only about 25% of an oral dose is absorbed, and the drug is excreted as rapidly as it is absorbed in normal renal function. About 80% of what is absorbed is bound to serum protein; tissue levels are highest in the kidney, with small amounts everywhere else including cerebrospinal fluid. Excretion is considerably delayed in neonates, young infants and renal impairment.
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · a recorded source, not a stored snapshot
The drug is shaped like the piece the wall-stitching enzyme expects, so the enzyme grabs it — and then cannot let go.
╌╌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 beta-lactam ring is a structural mimic of the D-alanyl-D-alanine terminus of the peptidoglycan pentapeptide. Penicillin-binding protein transpeptidases attack it, forming a stable acyl-enzyme intermediate that hydrolyses extremely slowly. The label describes this as inhibition of biosynthesis of cell-wall mucopeptide.
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · a recorded source, not a stored snapshot
A cell that is not building new wall has nothing to interrupt. The drug kills only organisms that are actively multiplying.
╌╌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 states penicillin V exerts a bactericidal action during the stage of active multiplication. It is not active against penicillinase-producing bacteria, which include many staphylococcal strains. Groups A, C, G, H, L and M streptococci are very sensitive; group D enterococci are resistant.
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · a recorded source, not a stored snapshot
The streptococcus is cleared — if the course is completed
Eradicating the organism, not relieving the sore throat, is what prevents rheumatic fever. That is why the duration is specified and why missing doses matters more here than usual.
╌╌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
Precautions: "In streptococcal infections, therapy must be sufficient to eliminate the organism (10-day minimum); otherwise the sequelae of streptococcal disease may occur." In a randomised comparison, five days at 800 mg four times daily gave bacteriological eradication of 80.4% against 90.7% for ten days at 1,000 mg three times daily, while matching on clinical cure.
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · a recorded source, not a stored snapshot
Eighty years, and the organism has never become resistant
Group A streptococcus has never produced a penicillin-resistant isolate. That is close to unique among antibiotics in continuous use since the 1940s.
╌╌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
Resistance would require alteration of the penicillin-binding proteins, and in this organism such alterations appear to carry an unacceptable fitness cost. Isolates with modestly reduced susceptibility and pbp2x substitutions have been reported and none has established clinical resistance. This is an empirical observation about one species, not a property of the drug, and continued minimum inhibitory concentration surveillance is how it stays known.
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · 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.
People with confirmed streptococcal pharyngitis or other streptococcal infection, and people with a history of rheumatic fever taking continuous prophylaxis against recurrence.
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
Only about 25% of an oral dose is absorbed, and the label records that some patients do not absorb therapeutic amounts at all
In a comparator arm on another drug’s label, oral penicillin four times daily for ten days eradicated the streptococcus in only 70% of children
The five-day regimen matched on symptoms and lost ten percentage points on eradication, which is the endpoint that matters for the complication being prevented
The cephalosporin cross-reactivity figure in the label’s all-capitals warning reflects an 8% estimate that later work put at about 2%
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
Prescription only
❝ 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 250 mg (400,000 units) and 500 mg (800,000 units) of penicillin V potassium, and an oral solution at 125 and 250 mg per 5 mL — typically taken three or four times 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
The potassium salt resists gastric acid inactivation, which is the property that makes an oral penicillin possible; average blood levels are two to five times those after the same oral dose of penicillin G with much less individual variation.
✎ 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: It may be given with meals, though levels are slightly higher fasting. Only about 25% of an oral dose is absorbed, roughly 80% of the absorbed drug is protein bound, and elimination is renal and as rapid as absorption in normal kidney function. Excretion is considerably delayed in neonates, young infants and renal impairment.
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
The label carries an all-capitals warning that serious and occasionally fatal hypersensitivity reactions have been reported, that they are more likely in individuals with a history of penicillin hypersensitivity or sensitivity to multiple allergens, and that individuals with a history of penicillin hypersensitivity have experienced severe reactions when treated with cephalosporins — a cross-reactivity now estimated at about 2% rather than the 8% previously reported. Serious anaphylaxis requires immediate epinephrine. Also carries the Clostridioides difficile-associated diarrhoea warning common to antibacterials, which the label notes may present over two months after the last dose. The oral route should not be relied on in severe illness or with vomiting or intestinal hypermotility, and severe pneumonia, empyema, bacteraemia, pericarditis, meningitis and arthritis should not be treated with penicillin V during the acute stage.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
Where this came from
Penicillin V potassium tablets United States prescribing information — Description, Clinical Pharmacology, Indications and Usage, Warnings, Precautions (http… · 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 250 mg (400,000 units) and 500 mg (800,000 units) of penicillin V potassium, and an oral solution at 125 and 250 mg per 5 mL — typically taken three or four times 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
It may be given with meals, though levels are slightly higher fasting.
✎ 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: Only about 25% of an oral dose is absorbed, roughly 80% of the absorbed drug is protein bound, and elimination is renal and as rapid as absorption in normal kidney function. Excretion is considerably delayed in neonates, young infants and renal impairment.
No source is stored against this line.
What is recorded as being sold
76 products list this as an active ingredient in the United States drug directory. 76 of them contain it and nothing else.
FDA National Drug Code directory · 72789-222 · read 2026-08-29
They are sold as powder, powder, for solution, tablet and tablet, film coated, taken oral.
FDA National Drug Code directory · 72789-222 · read 2026-08-29
The regulator's established pharmacologic class for it is penicillin-class antibacterial [epc] and penicillins [cs].
FDA National Drug Code directory · 72789-222 · read 2026-08-29
60 published labels name it as an active ingredient. 60 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · b6bb14f3-c916-4abd-b967-862eb4f858eb · read 2026-08-29
Those labels are classed as human prescription drug.
US prescribing information · b6bb14f3-c916-4abd-b967-862eb4f858eb · read 2026-08-29
3893 marketed supplement labels list this ingredient, classed as botanical, non-nutrient/non-botanical and other combinations.
Those labels carry all other, nutrient and structure/function claims. A claim of that kind is written by the manufacturer and is not assessed by any regulator, so its presence says nothing about whether it is true.
Penicillin V Potassium is oral at HOW SUPPLIED Penicillin V Potassium Tablets USP, 500 mg (800,000 units) are white to off-white, capsule shaped, film-coated tablets, debossed with 'E' and a break line on one side and '8' and '5' separated with a break…, recorded as fda label in effect 2023-03-16 in the United States.
US prescribing information · b6bb14f3-c916-4abd-b967-862eb4f858eb · 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 Phenoxymethylpenicillin 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 ten-day minimum in the label is a trial-established duration rather than eradication-based reasoning from the 1950s
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 oral penicillin V has the rheumatic fever prevention evidence — the demonstrated formulation is intramuscular penicillin, as another drug’s label states outright
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 a recorded penicillin allergy is a real one; under 5% of people reporting it have confirmed hypersensitivity and 80% of genuine cases become tolerant within a decade
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 oral penicillin prevents bacterial endocarditis before dental procedures — its own label states no controlled clinical efficacy studies have been conducted
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.
How much did people take in the studies?
The sources RNAWiki checked hold nothing for this field.
Why it matters. A result belongs to an amount. Without the amount the result floats free.
What would answer it
A stored source that records 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 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 Phenoxymethylpenicillin 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.
Almost everyone labelled penicillin-allergic is not
In plain words
About one American in ten reports a penicillin allergy. Fewer than one in twenty of those turns out to have a real one, and even genuine allergy fades — four in five people lose it within ten years.
What was measured
Proportion of reported penicillin allergy that is confirmed hypersensitivity, waning over time, and penicillin-cephalosporin cross-reactivity rate
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Approximately 10% of the United States population reports a penicillin allergy, with higher rates among older and hospitalised patients, while clinically significant IgE-mediated or T-lymphocyte-mediated penicillin hypersensitivity is uncommon, at under 5%. IgE-mediated penicillin allergy wanes over time, with 80% of patients becoming tolerant after a decade, and the rate of IgE-mediated allergy is falling, potentially because parenteral penicillins are used less and severe anaphylaxis to oral amoxicillin is rare. Cross-reactivity between penicillins and cephalosporins occurs in about 2% of cases, less than the 8% previously reported — a figure that matters because penicillin V’s own label carries an all-capitals warning that individuals with a history of penicillin hypersensitivity have experienced severe reactions when treated with cephalosporins. Low-risk histories include isolated non-allergic symptoms such as gastrointestinal upset, a family history alone, pruritus without rash, and a remote unknown reaction more than ten years ago; high-risk histories include anaphylaxis, positive skin testing, recurrent reactions and multiple beta-lactam hypersensitivities. The consequence of an unexamined label is not neutral: substituting broad-spectrum antibiotics raises the risk of MRSA, vancomycin-resistant enterococcus and Clostridioides difficile.
Written into the record, not signed off as a reviewed claim
The ten-day course is in the label and was never established by trial
In plain words
Ten days is the rule for strep throat, and the label says so. A randomised trial of 433 patients found five days at a higher frequency worked as well on cure, with fewer side effects — and worse organism clearance.
What was measured
That the ten-day minimum in the label reflects a duration established by trial — it reflects the eradication-based reasoning of the 1950s, and the one modern randomised comparison found five days non-inferior on clinical cure while worse on eradication
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The Precautions section of the label states: "In streptococcal infections, therapy must be sufficient to eliminate the organism (10-day minimum); otherwise the sequelae of streptococcal disease may occur." An open-label randomised non-inferiority trial at 17 Swedish primary care centres enrolled 433 patients aged 6 and over with group A streptococcal pharyngotonsillitis and three or four Centor criteria, comparing penicillin V 800 mg four times daily for five days (16 g total) with 1,000 mg three times daily for ten days (30 g total), with a pre-specified non-inferiority margin of 10 percentage points. Clinical cure in the per-protocol population was 89.6% (181/202) on five days against 93.3% (182/195) on ten, 95% CI -9.7 to 2.2 — non-inferior. Time to symptom relief was shorter on the five-day regimen, and the ten-day group had a higher incidence and longer duration of adverse events. The result that complicates the story is bacteriological: eradication was 80.4% (156/194) on five days against 90.7% (165/182) on ten. Since the mechanism by which treatment prevents rheumatic fever is eradication rather than symptom relief, a regimen that matches on symptoms and loses ten points on eradication is not obviously equivalent for the reason the infection is treated. Relapses were 8 against 7 and complications 0 against 4.
Written into the record, not signed off as a reviewed claim
It does prevent rheumatic fever — in trials run when rheumatic fever was common
In plain words
Pooled placebo-controlled trials show antibiotics cut acute rheumatic fever after a sore throat by about two-thirds. Most of those trials were run in the 1950s, when the complication was many times more common than it is now.
What was measured
Acute rheumatic fever, suppurative complications and symptoms after antibiotic treatment of sore throat, against placebo or no treatment
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A Cochrane review of 29 randomised or quasi-randomised trials in 15,337 cases of sore throat found antibiotics reduced acute rheumatic fever within two months against control (Peto odds ratio 0.36, 95% CI 0.26 to 0.50; 18 studies, 12,249 participants; moderate-certainty evidence). The review states directly that the majority of included studies were conducted in the 1950s, when rates of serious complications — especially acute rheumatic fever — were much higher than today, and that the overall prevalence of acute rheumatic fever was very low, particularly in the later studies. Antibiotics also reduced acute otitis media within 14 days (Peto OR 0.21, 0.11 to 0.40, high certainty) and quinsy within two months (Peto OR 0.16, 0.07 to 0.35, high certainty) but not acute sinusitis (Peto OR 0.46, 0.10 to 2.05), and there were too few cases of acute glomerulonephritis to determine an effect. The relative risk reduction is real and well measured. The absolute benefit it converts into depends entirely on the baseline rate of rheumatic fever in the population being treated, and that rate has fallen by orders of magnitude in high-income countries since the trials were done, while remaining high in much of the world.
Written into the record, not signed off as a reviewed claim
For symptoms alone, the benefit is small and most people recover anyway
In plain words
Eighty-two per cent of untreated people were symptom-free within a week. Antibiotics helped one extra person in about six be free of sore throat at day three, and one in eighteen at one week, and did not reduce fever at day three at all.
What was measured
That treating a sore throat with penicillin produces a symptomatic benefit large enough to justify the prescription on its own — the pooled effect is a number needed to treat below six at day three and 18 at one week, with 82% of untreated participants symptom-free by one week and no significant effect on fever
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
In the same Cochrane review, throat soreness at day three was reduced (risk ratio 0.70, 95% CI 0.60 to 0.80; 16 studies, 3,730 participants; moderate certainty) with a number needed to treat below six, and at one week (RR 0.50, 0.34 to 0.75; 14 studies, 3,083 participants) with a number needed to treat of 18 — the larger relative effect at one week reflecting how few cases remained unresolved in either arm by then. Antibiotics did not significantly reduce fever at day three (RR 0.75, 95% CI 0.53 to 1.07; 8 studies, 1,443 participants; high-certainty evidence) but did reduce headache (RR 0.49, 0.34 to 0.70; high certainty). Eighty-two per cent of participants in the placebo or no-treatment arms were symptom-free by one week. The review notes that harms from antibiotics were poorly or inconsistently reported and could not be quantified, so the benefit side of this comparison is measured considerably better than the harm side. The authors conclude that because the effect on symptoms can be small, clinicians must judge case by case whether it is justifiable and whether the cause is likely to be bacterial at all — few of the included studies distinguished bacterial from viral aetiology.
Written into the record, not signed off as a reviewed claim
The label admits there are no controlled studies for endocarditis prophylaxis
In plain words
Penicillin V has been recommended for decades to prevent heart valve infection before dental work. Its own label states that no controlled clinical efficacy studies have been conducted.
What was measured
Controlled clinical efficacy evidence for oral penicillin prophylaxis against bacterial endocarditis: none, per the label
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The Indications and Usage section states: "Although no controlled clinical efficacy studies have been conducted, penicillin V has been suggested by the American Heart Association and the American Dental Association for use as an oral regimen for prophylaxis against bacterial endocarditis in patients who have congenital heart disease or rheumatic or other acquired valvular heart disease when they undergo dental procedures and surgical procedures of the upper respiratory tract." It then narrows the recommendation twice over: oral penicillin should not be used in patients at particularly high risk, such as those with prosthetic valves or surgically constructed systemic pulmonary shunts, and penicillin V should not be used as adjunctive prophylaxis for genitourinary or gastrointestinal procedures. This is a labelled indication whose evidence base is expert recommendation, stated as such in the document that carries it — which is rarer and more honest than it sounds, and it is the reason guideline bodies on both sides of the Atlantic have progressively narrowed endocarditis prophylaxis over the past two decades.
Source
Penicillin V potassium tablets United States prescribing information, Indications and Usage
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
Injected penicillin stopped rheumatic heart disease progressing in Uganda
In plain words
In 818 Ugandan children found on screening to have early rheumatic heart disease, monthly penicillin injections for two years produced progression in 0.8% against 8.2% with no prophylaxis.
What was measured
Echocardiographic progression of latent rheumatic heart disease at 2 years with four-weekly benzathine penicillin G
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A randomised controlled trial screened 102,200 children and adolescents by echocardiography; 3,327 were initially assessed as having latent rheumatic heart disease and 926 received a definitive diagnosis on confirmatory echocardiography. Of these, 916 underwent randomisation to penicillin G benzathine injections every four weeks for two years or no prophylaxis, with 818 in the modified intention-to-treat analysis and 799 (97.7%) completing. Echocardiographic progression at two years occurred in 3 participants (0.8%) on prophylaxis against 33 (8.2%) in the control group — a risk difference of -7.5 percentage points (95% CI -10.2 to -4.7, p<0.001). Two participants had serious adverse events attributable to prophylaxis, including one mild anaphylactic reaction, representing under 0.1% of all administered doses. Two things are worth separating. This is the strongest modern evidence for penicillin in rheumatic disease and it is for the injected depot formulation, not the oral tablet — the same distinction cefdinir’s label draws when it says only intramuscular penicillin has been demonstrated to prevent rheumatic fever. And it is secondary prophylaxis in people who already have detectable valve damage, which is a different population from a child with a sore throat.
Written into the record, not signed off as a reviewed claim
Only a quarter of the dose is absorbed, and four times daily is why
In plain words
The label states that only about 25% of an oral dose gets in, and that some people simply do not absorb a therapeutic amount at all. That is the reason for a four-times-daily schedule nobody completes.
What was measured
Fraction of an oral dose absorbed, and bacteriological eradication achieved by oral penicillin four times daily in a paediatric comparator arm
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
The Clinical Pharmacology section states that the drug is excreted as rapidly as it is absorbed in people with normal kidney function, and that recovery from urine indicates only about 25% of an oral dose is absorbed. The Precautions section adds that the oral route should not be relied on in severe illness or with nausea, vomiting, gastric dilatation, cardiospasm or intestinal hypermotility, and that "occasionally patients will not absorb therapeutic amounts of orally administered penicillin". Poor and variable absorption, combined with rapid renal clearance and the time-dependent pharmacodynamics of beta-lactams, is what produces the four-times-daily regimen. The clinical consequence is visible in a comparator arm on another drug’s label: in cefdinir’s paediatric pharyngitis registration studies, oral penicillin at 10 mg/kg four times daily for ten days eradicated Streptococcus pyogenes in 159 of 227 children — 70% — against cefdinir’s 94%. Penicillin has not become less active against the organism; the regimen delivering it is simply hard to complete, and a drug that is not taken is indistinguishable from a drug that does not work.
Source
Penicillin V potassium tablets United States prescribing information, Clinical Pharmacology and Precautions; cefdinir United States prescribing information, Clinical Studies — Streptococcal Pharyngitis/Tonsillitis
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)
Z61I075U2W
CAS registry number
87-08-1
PubChem compound
6869
ChEMBL
CHEMBL615
ChEBI
27446
WHO international nonproprietary name list entry
518
RxNorm concept
7984
EMA substance identifier
100000090361
European Chemicals Agency number
201-722-0
DrugBank
DB00417
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No registered study is classified as testing this substance.
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Safety mode resolved
No register row and no identity class settled the question.
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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.
What the approval register records
37 approved applications cover products containing this substance. The earliest was ANDA060006, approved 19580113 to WYETH AYERST.
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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.
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How close this is to real life — found nothing in the sources checked.
Felt, measured, or meaningful — found nothing in the sources checked.
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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.
The narrowest and cheapest antibiotic here, against an organism that has never developed resistance to it, whose pooled placebo-controlled trials — mostly conducted in the 1950s — cut acute rheumatic fever with a Peto odds ratio of 0.36 across 12,249 participants while shortening a sore throat by an amount requiring fewer than six people treated to help one at day three and eighteen at one week, and whose label directs a ten-day minimum course that a 433-patient randomised trial found five days matched on clinical cure.
Recorded evidence blocks (7)
Q1
On the Phenoxymethylpenicillin label: indicated for what?
"To reduce the development of drug-resistant bacteria and maintain the effectiveness of penicillin V potassium and other antibacterial drugs, penicillin V potassium should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and…": indications and usage on Phenoxymethylpenicillin's label. DailyMed label · 861ccfaa-8b7a-0def-e053-2991aa0a1a39 · 2026-08-21
Q2
12 registered trials of Phenoxymethylpenicillin — at which phases?
"Insufficient enrollment."; 3 of 12 registered studies
Show the evidence
Trial
NCT00823433
terminated; "Insufficient enrollment."
NCT02099240
terminated; "Not enough patient enrollment and lack of staffing"
NCT03208361
terminated; "Lack of financial support to continue with the study recruitment. Independent study financially supported by a national grant with a 4.5 years duration."
recorded 2026-09-01 · last checked 2026-09-04
Q4
Which 5 trials of Phenoxymethylpenicillin posted no result?
Posted no result
5 of 5 completed trials
Registrations
NCT02188472, NCT01499875, NCT01368341, NCT02712307 and NCT04084106
Completion dates
oldest 2011-02; newest 2022-11-11
Show the evidence
Trial
NCT02188472
2011-02
NCT01499875
2013-08
NCT01368341
2014-12
NCT02712307
2018-06
NCT04084106
2022-11-11
Q5
At the median, Phenoxymethylpenicillin's trials enrolled 152 people — anything larger?
Median enrolment
152
Largest enrolment
9622
Registered trials counted
12
Q6
What do 439 spontaneous reports say about Phenoxymethylpenicillin — 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.
Phenoxymethylpenicillin appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 439 reaction mentions were counted: drug hypersensitivity 199; rash 65; urticaria 52; anaphylactic reaction 22. FAERS via Open Targets · CHEMBL1200852 · 2026-06-24
Show the evidence
drug hypersensitivity
199
rash
65
urticaria
52
anaphylactic reaction
22
hypersensitivity
19
encephalopathy
18
4 more recorded rows
toxicity to various agents
18
swelling
16
liver injury
15
suicide attempt
15
recorded 2026-06-24 · last checked 2026-09-04
Q7
Which 10 reactions does Phenoxymethylpenicillin's label not list?
ChEMBL 37 — CC BY-SA 3.0 Unported · ClinicalTrials.gov — US Government work · Open Targets 26.06 — CC0 · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — 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
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✓ source coverage passed: 5 source rows
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✓ canonical metadata passed: slug and display name present
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This is a record of evidence. It is not medical advice, and it does not say this substance suits you. Nothing here says any substance on RNAWiki is appropriate for a child.