This page shows what was measured, who it was measured in, and what that does not settle.
What Nirmatrelvir-ritonavir does in the body
Early COVID-19 in adults at high risk of becoming seriously ill
The virus builds all its proteins as one long ribbon and then cuts the ribbon into working parts using a pair of molecular scissors. Nirmatrelvir slots into those scissors and locks them. Without the cuts, none of the parts work and the virus cannot assemble copies of itself. The second drug in the pack, ritonavir, does nothing to the virus: your liver would otherwise destroy nirmatrelvir within an hour or two, and ritonavir blocks the liver enzyme that does it. That is also why the pack has so many drug interactions.
What happened in people
COVID-19 hospitalisation or death of 0.77% against 7.01% in unvaccinated high-risk adults treated within three days, with all 13 deaths in the placebo group
✎ 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.
The ritonavir component, present only as a pharmacokinetic booster, is the source of an interaction burden that determines whether the drug can be given at all in many patients
Where it acts
Cytoplasm of infected respiratory epithelial cells; hepatic CYP3A4 for ritonavir
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
Its recorded molecular formula is C23H32F3N5O4, weighing 499.54.
US prescribing information · 8a99d6d6-fd9e-45bb-b1bf-48c7f761232a · read 2026-08-30
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 130 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.
COVID-19-related hospitalisation or death from any cause through day 28 in unvaccinated high-risk adults
P < 0.001 (relative risk reduction 89.1% in the interim analysis)
Repeated elsewhere
Partially 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. The population was unvaccinated and enrolled during the Delta period, so the absolute risk in the placebo arm, 7.01%, is far higher than in a comparable population today.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral co-packaged dose pack: nirmatrelvir tablets plus ritonavir tablets
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
COVID-19 hospitalisation and death during the Omicron surge
✓ The study showed what it set out to show
Who was studied
Clalit Health Services Omicron cohort
How many people
109254
Study design
Retrospective cohort with time-dependent covariates
Compared against
Not recorded for this study
Kind of result
Living longer, or avoiding a major event
What was found
Adjusted hazard ratio 0.27 (95% CI 0.15 to 0.49) for hospitalisation in those aged 65 and over; 0.74 (95% CI 0.35 to 1.58) in those aged 40 to 64
Repeated elsewhere
Partially 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. Observational. Only 4% of eligible patients received the drug, so treated and untreated groups differed in ways adjustment can reduce but not remove.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral co-packaged dose pack: nirmatrelvir tablets plus ritonavir tablets
Interval reported. 95% CI 0
Written into the record, not signed off as a reviewed claim.
Retrospective analysis of a randomised placebo-controlled platform trial
Compared against
A dummy treatment
Kind of result
A number that stands in for health
What was found
Symptom rebound 26%, viral rebound 31%, high-level viral rebound 13%, all without any antiviral treatment
Repeated elsewhere
Partially 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. Largely unvaccinated participants infected with pre-Omicron variants, so the natural-history rates may not transfer to the current population.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral co-packaged dose pack: nirmatrelvir tablets plus ritonavir tablets
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
RNAWiki holds 4 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
Nirmatrelvir-ritonavir
What a person takes: Oral co-packaged dose pack: nirmatrelvir tablets plus ritonavir tablets.
The measurement behind this step
Three tablets twice daily for five days, taken together, started within five days of symptom onset. Separate dose packs exist for moderate renal impairment. The co-packaging is not a convenience: nirmatrelvir alone does not reach antiviral concentrations because CYP3A4 clears it too quickly, so the ritonavir tablet is a pharmacokinetic component of the dose rather than a second treatment.
Getting in
Two different tablets, taken together, for two different jobs
The pack contains the antiviral and a booster. The booster is not there to fight the virus.
──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
Each dose is nirmatrelvir 300 mg plus ritonavir 100 mg, twice daily for five days, started within five days of symptom onset. Without ritonavir, nirmatrelvir plasma concentrations fall below the target trough because of rapid CYP3A4 metabolism.
Ritonavir blocks the liver enzyme that would clear the antiviral
The booster shuts down a liver enzyme, so the antiviral survives in the blood long enough to reach the virus.
──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
Ritonavir is a mechanism-based inactivator of CYP3A4, raising nirmatrelvir exposure several-fold. The same inhibition raises exposure to every other CYP3A4 substrate the patient is taking, which is the origin of the interaction list rather than an unrelated side effect.
Nirmatrelvir docks into the viral protease active site
The antiviral is shaped to fit the pocket where the virus scissors grip what they are about to cut.
──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
Nirmatrelvir occupies the S1, S2 and S4 subsites of the SARS-CoV-2 main protease; the gamma-lactam mimics the glutamine that the enzyme requires at the P1 position, which is the specificity determinant with no close human counterpart.
A nitrile warhead forms a reversible covalent bond with the catalytic cysteine
A reactive group on the drug bonds to the exact atom the enzyme uses to cut, and holds 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
The terminal nitrile reacts with the thiol of cysteine 145 to form a reversible covalent thioimidate adduct. Because the bond is reversible, potency depends on maintaining plasma concentration, which is again why the ritonavir boost is not optional.
The viral polyprotein is never cut, so no functional virus is assembled
The long protein ribbon stays uncut, none of the parts work, and viral replication stops.
╌╌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
Inhibition of Mpro prevents cleavage of the ORF1ab polyproteins into the non-structural proteins required for replication. In EPIC-HR this produced a 0.868 log10 lower day-5 viral load and an 89% relative reduction in hospitalisation or death in the unvaccinated high-risk population studied.
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 5 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 mild-to-moderate COVID-19 within five days of symptom onset who are at high risk of progression, most importantly people aged 65 and over and those with significant immunosuppression.
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.
What the label states about particular groups
On pediatric, the label states: “The optimal dose of PAXLOVID has not been established in pediatric patients.”
US prescribing information · 8a99d6d6-fd9e-45bb-b1bf-48c7f761232a · read 2026-08-30
On older people, the label states: “Clinical studies of PAXLOVID include subjects 65 years of age and older and their data contributes to the overall assessment of safety and efficacy [see Adverse Reactions (6.1) and Clinical Studies (14.1) ] .”
US prescribing information · 8a99d6d6-fd9e-45bb-b1bf-48c7f761232a · read 2026-08-30
On people who are pregnant, the label states: “Risk Summary Available data on the use of nirmatrelvir during pregnancy are insufficient to evaluate for a drug-associated risk of major birth defects, miscarriage, or adverse maternal or fetal outcomes.”
US prescribing information · 8a99d6d6-fd9e-45bb-b1bf-48c7f761232a · read 2026-08-30
On people who are breastfeeding, the label states: “Risk Summary Nirmatrelvir and ritonavir are present in human breast milk in small amounts (less than 2%).”
US prescribing information · 8a99d6d6-fd9e-45bb-b1bf-48c7f761232a · read 2026-08-30
On people with reduced liver function, the label states: “No dosage adjustment of PAXLOVID is recommended for patients with mild (Child-Pugh Class A) or moderate (Child-Pugh Class B) hepatic impairment.”
US prescribing information · 8a99d6d6-fd9e-45bb-b1bf-48c7f761232a · read 2026-08-30
On people with reduced kidney function, the label states: “increases nirmatrelvir exposure, which may increase the risk of PAXLOVID adverse reactions.”
US prescribing information · 8a99d6d6-fd9e-45bb-b1bf-48c7f761232a · read 2026-08-30
Where the result stopped carrying
EPIC-SR missed its primary symptom endpoint and was terminated
The Omicron-era observational cohort found no significant benefit in adults aged 40 to 64
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 co-packaged dose pack: nirmatrelvir tablets plus ritonavir tablets
✎ 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
Three tablets twice daily for five days, taken together, started within five days of symptom onset. Separate dose packs exist for moderate 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: The co-packaging is not a convenience: nirmatrelvir alone does not reach antiviral concentrations because CYP3A4 clears it too quickly, so the ritonavir tablet is a pharmacokinetic component of the dose rather than a second treatment.
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
Dysgeusia, a persistent metallic taste, occurred in 5.6% of treated participants in EPIC-HR against 0.3% on placebo, and diarrhoea in 3.1% against 1.6%. Serious adverse events were less frequent on treatment than on placebo in EPIC-HR, 1.6% against 6.6%, reflecting the illness the drug was preventing. The dominant safety issue is the ritonavir interaction profile, which requires a medication review before the first dose and dose adjustment in renal impairment.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
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∅Nothing found in the sources checked
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 co-packaged dose pack: nirmatrelvir tablets plus ritonavir tablets
✎ 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
Separate dose packs exist for moderate 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: The co-packaging is not a convenience: nirmatrelvir alone does not reach antiviral concentrations because CYP3A4 clears it too quickly, so the ritonavir tablet is a pharmacokinetic component of the dose rather than a second treatment.
No source is stored against this line.
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 Nirmatrelvir-ritonavir 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 89% relative risk reduction from EPIC-HR describes the benefit for a vaccinated adult under 65 — the trial designed to answer that missed its primary endpoint
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 rebound is caused by the drug, when a quarter to a third of untreated patients rebound by the same definitions
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 Nirmatrelvir-ritonavir 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.
EPIC-HR: 0.77% versus 7.01% hospitalisation or death, an 89% relative reduction
In plain words
In unvaccinated adults with risk factors, treated within three days of symptoms, three of 389 were hospitalised or died against 27 of 385 on placebo, and all the deaths were in the placebo group.
What was measured
COVID-19-related hospitalisation or death from any cause through day 28
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Phase 2-3 double-blind randomised trial in symptomatic, unvaccinated, non-hospitalised adults at high risk of progression. 2,246 randomised. In the planned interim analysis of patients treated within 3 days of symptom onset, COVID-19-related hospitalisation or death from any cause by day 28 was 0.77% (3 of 389) versus 7.01% (27 of 385), a difference of -6.32 percentage points (95% CI -9.04 to -3.59; P<0.001; relative risk reduction 89.1%). In the final modified intention-to-treat analysis of 1,379 patients the difference was -5.81 percentage points (95% CI -7.78 to -3.84; relative risk reduction 88.9%). All 13 deaths occurred in the placebo group. Day-5 viral load was 0.868 log10 copies per millilitre lower.
Written into the record, not signed off as a reviewed claim
EPIC-SR: the primary endpoint was missed in vaccinated and standard-risk adults
In plain words
When the same drug was tested in people who were vaccinated or at standard risk, symptoms took 12 days to settle on treatment and 13 on placebo, a difference that was not statistically significant.
What was measured
Time to sustained alleviation of all targeted COVID-19 signs and symptoms
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
Phase 2-3 trial in adults with COVID-19 within 5 days of symptom onset who were either fully vaccinated with at least one risk factor, or without risk factors and unvaccinated or not vaccinated within the previous year. 1,296 randomised, 1,288 treated and analysed. Median time to sustained alleviation of all targeted signs and symptoms was 12 days on nirmatrelvir-ritonavir and 13 on placebo (P=0.60). COVID-19 hospitalisation or death from any cause occurred in 5 of 654 (0.8%) and 10 of 634 (1.6%), difference -0.8 percentage points (95% CI -2.0 to 0.4). The trial was terminated. Dysgeusia occurred in 5.8% of treated participants.
Written into the record, not signed off as a reviewed claim
Omicron-era effectiveness was confined to people aged 65 and over
In plain words
In a real-world analysis of 109,254 eligible Israeli patients during Omicron, the drug clearly reduced hospitalisation and death in over-65s and showed no benefit in adults aged 40 to 64.
What was measured
Adjusted hazard ratios for COVID-19 hospitalisation and death by age stratum
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Retrospective cohort of Clalit Health Services members aged 40 and over assessed as eligible for nirmatrelvir during the Omicron surge; 3,902 of 109,254 received it. In patients aged 65 and over, COVID-19 hospitalisation was 14.7 versus 58.9 cases per 100,000 person-days, adjusted hazard ratio 0.27 (95% CI 0.15 to 0.49), and death 0.21 (95% CI 0.05 to 0.82). In patients aged 40 to 64, hospitalisation was 15.2 versus 15.8 per 100,000 person-days, adjusted hazard ratio 0.74 (95% CI 0.35 to 1.58), and death 1.32 (95% CI 0.16 to 10.75). Observational, with time-dependent covariate adjustment.
Written into the record, not signed off as a reviewed claim
Rebound was attributed to the drug before anyone measured it without the drug
In plain words
Symptoms and viral load coming back after treatment became a widely reported problem. When the placebo arm of another trial was examined, rebound turned out to be common without any treatment at all.
What was measured
That symptom or viral rebound after a course of nirmatrelvir-ritonavir is caused by the drug
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A retrospective analysis of the 563 placebo recipients in the ACTIV-2/A5401 platform trial found symptom rebound in 26% at a median of 11 days after symptom onset, viral rebound in 31% and high-level viral rebound in 13%, with 89% of symptom rebound and 95% of viral rebound events occurring at a single time point before improving. The combination of symptom and high-level viral rebound occurred in 3%. A separate prospective cohort found viral rebound in 14.2% of 127 treated participants and 9.3% of 43 untreated controls, and symptom rebound in 18.9% against 7.0%; the untreated comparison group was small. The honest position is that rebound occurs with and without treatment, and that the drug-attributable excess has not been cleanly quantified.
Written into the record, not signed off as a reviewed claim
Half the product is not an antiviral, and it is the half that causes the problems
In plain words
Ritonavir contributes nothing against the virus. It is there only to stop the liver clearing nirmatrelvir, and it is the reason the drug interacts with so many medicines.
What was measured
Not recorded
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Nirmatrelvir is cleared by CYP3A4 fast enough that plasma concentrations fall below the antiviral threshold without a booster. Ritonavir 100 mg twice daily is co-packaged as a potent mechanism-based CYP3A4 inhibitor at a dose far below its own antiretroviral dose. The consequence is a large interaction list: statins, several antiarrhythmics, some anticoagulants, calcineurin inhibitors such as tacrolimus, and various sedatives and ergot derivatives require adjustment, suspension or are contraindicated. The interaction burden is a property of the delivery strategy rather than of the antiviral, which is a distinction worth making because remdesivir treats the same disease without it.
Source
PAXLOVID (nirmatrelvir tablets and ritonavir tablets) US prescribing information, drug interactions section
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
The drug went from emergency authorisation to full approval while the population it treats changed underneath it
In plain words
The approval evidence came from unvaccinated people during Delta. By the time full approval arrived, almost everyone eligible had immunity from vaccination or infection.
What was measured
Not recorded
Effect estimate
No reviewed effect estimate exists for this record.
Limits
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From the source
Nirmatrelvir-ritonavir received emergency use authorisation in December 2021 on EPIC-HR, which enrolled unvaccinated adults during the Delta period. Full FDA approval followed on 25 May 2023 under NDA 217188. Between those dates, EPIC-SR failed its primary endpoint in vaccinated and standard-risk adults and the Clalit cohort found benefit confined to those aged 65 and over. The label indication is restricted to adults at high risk of progression, which is the population in whom the absolute benefit survives the change in background immunity.
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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.
A protease inhibitor plus a pharmacokinetic booster that cut COVID-19 hospitalisation or death from 7.01% to 0.77% in unvaccinated high-risk adults, and missed its primary symptom endpoint in vaccinated and standard-risk adults with a hospitalisation difference of 0.8 percentage points that crossed zero.
Recorded evidence blocks (8)
Q1
On the Nirmatrelvir-ritonavir label: indicated for what?
"PAXLOVID is indicated for the treatment of mild-to-moderate coronavirus disease 2019 (COVID-19) in adults who are at high risk for progression to severe COVID-19, including hospitalization or death. ( 1 ) Limitations of Use PAXLOVID is not approved for use as pre-exposure or post-exposure prophylaxis for prevention of…": indications and usage on Nirmatrelvir-ritonavir's label. DailyMed label · 8a99d6d6-fd9e-45bb-b1bf-48c7f761232a · 2026-08-30
Q2
44 registered trials of Nirmatrelvir-ritonavir — at which phases?
Registered studies posting no result
35 of 44
44 registered studies of Nirmatrelvir-ritonavir: 16 na or unstated, 9 phase3, 7 phase1, 7 phase2, 4 phase4, 1 early phase1, 1 na. CLINICALTRIALS_SNAPSHOT · 2026-09-01
40 with a PubMed record
Show the evidence
na or unstated
16
phase3
9
phase1
7
phase2
7
phase4
4
early phase1
1
8 more recorded rows
na
1
completed
21
unknown
9
recruiting
7
withdrawn
3
active not recruiting
2
not yet recruiting
1
terminated
1
recorded 2026-09-01 · last checked 2026-09-04
Q3
4 of Nirmatrelvir-ritonavir's trials stopped: safety, accrual/recruitment, other?
"Decision to terminate study was due to slow enrolment and FDA input that available data may be enough for dosing recommendations for severe renal disease (subject to review by FDA)."; 4 of 44 registered studies
Show the evidence
Trial
NCT05487040
terminated; "Decision to terminate study was due to slow enrolment and FDA input that available data may be enough for dosing recommendations for severe renal disease (subject to review by FDA)."
NCT05545319
withdrawn; "Termination due to challenges related to the operational feasibility of the study, taking into account the current epidemiology and declining hospitalization rates for severe COVID-19."
NCT05997485
withdrawn; "The study was prematurely discontinued due to the substantial delay in initiation the study. This decision was not due to major safety concerns or requests from any regulatory authorities."
NCT06397144
withdrawn; "Sponsor business decision to terminate study. Decision not due to major safety concerns or requests from any regulatory authorities."
recorded 2026-09-01 · last checked 2026-09-04
Q4
Human studies of Nirmatrelvir-ritonavir used Nirmatrelvir 150 mg + Ritonavir 100 mg (Reference first dose) — over how long?
Human studies of Nirmatrelvir-ritonavir used "Nirmatrelvir 150 mg + Ritonavir 100 mg (Reference first dose)". ClinicalTrials.gov · 2026-09-01
Show the evidence
humanNCT05491330
Nirmatrelvir 150 mg + Ritonavir 100 mg (Reference first dose)
recorded 2026-09-01 · last checked 2026-09-04
Q5
Which running trial of Nirmatrelvir-ritonavir could settle lifespan?
NCT02735707 measures All-cause mortality, reading out 2028-02.
2 open trials; n 20000; "Randomized, Embedded, Multifactorial Adaptive Platform Trial for Community- Acquired Pneumonia"
Show the evidence
Trial
NCT02735707
"Randomized, Embedded, Multifactorial Adaptive Platform Trial for Community- Acquired Pneumonia"; n 20000; "All-cause mortality"; 2028-02
NCT04381936
"Randomised Evaluation of COVID-19 Therapy"; n 70000; "Community-acquired pneumonia: All-cause mortality (with subsidiary analyses of cause of death and of death at various timepoints following discharge)"; 2038-09-30
Q6
Which 9 trials of Nirmatrelvir-ritonavir posted no result?
Posted no result
9 of 9 completed trials
Registrations
NCT05341609, NCT05601167, NCT06735300, NCT05491330, NCT05813600 and NCT05624840, and 3 more
Completion dates
oldest 2022-05-31; newest 2024-08-01
Show the evidence
Trial
NCT05341609
2022-05-31
NCT05601167
2022-06-01
NCT06735300
2022-10-07
NCT05491330
2022-10-27
NCT05813600
2022-12
NCT05624840
2023-02-01
3 further recorded trials
NCT05321394
2023-10-29
NCT06349655
2024-03-10
NCT05690646
2024-08-01
Q7
At the median, Nirmatrelvir-ritonavir's trials enrolled 337 people — anything larger?
Median enrolment
337
Largest enrolment
131005
Registered trials counted
44
Q8
Nirmatrelvir-ritonavir and BCRP, CYP3A4 and OATP1B1: shared by which compounds?
Nirmatrelvir is a substrate for P-gp, but not BCRP, MATE1, MATE2K, NTCP, OAT1, OAT2, OAT3, OCT1, OCT2, PEPT1, OATP1B1, OATP1B3, OATP2B1, or OATP4C1. 12.4 Microbiology Mechanism of Action Nirmatrelvir is a peptidomimetic inhibitor of the SARS-CoV-2 main protease (M pro ), also referred to as 3C-like protease (3CL pro ) or nonstructural protein 5 (nsp5) protease.
pharmacokinetics
Nirmatrelvir is a substrate for P-gp, but not BCRP, MATE1, MATE2K, NTCP, OAT1, OAT2, OAT3, OCT1, OCT2, PEPT1, OATP1B1, OATP1B3, OATP2B1, or OATP4C1.
pharmacokinetics
Ritonavir is an inducer of CYP1A2, CYP2C9, CYP2C19, CYP2B6, and CYP3A.
pharmacokinetics
Nirmatrelvir is an inducer of CYP2B6, 2C8, 2C9, and 3A4, but there is minimal risk for pharmacokinetic interactions arising from induction of these CYP enzymes at the proposed therapeutic dose. • Ritonavir is a substrate of CYP2D6 and CYP3A.
ClinicalTrials.gov — US Government work · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
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