Nirmatrelvir/ritonavir

Pronunciation: nir-MA-trel-vir / ri-TON-a-vir.

Generic name
nirmatrelvir and ritonavir
Drug class
Oral antiviral combination -- SARS-CoV-2 main protease inhibitor (nirmatrelvir) plus a pharmacokinetic-boosting CYP3A inhibitor (ritonavir)
Form
Co-packaged tablets: nirmatrelvir 150 mg tablets and ritonavir 100 mg tablets
Route
Oral
Legal status
Prescription-only

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: Paxlovid (5) · Full directory

What nirmatrelvir and ritonavir is and how it works

Paxlovid is a prescription-only oral antiviral treatment for mild-to-moderate COVID-19 in people at high risk of the illness becoming severe. It combines nirmatrelvir, which directly blocks the virus from multiplying, with a low dose of ritonavir, which boosts nirmatrelvir's levels in the body. (1)

Paxlovid is taken as a 5-day course, started as soon as possible (and within 5 days of symptoms starting) after a positive COVID-19 test. Because ritonavir interacts with many other medicines, it is essential that your prescriber or pharmacist reviews everything you currently take before you start.

Mechanism of action: how nirmatrelvir and ritonavir works

Nirmatrelvir is a peptidomimetic inhibitor of the SARS-CoV-2 main protease (Mpro, also called 3CL protease), an enzyme required for viral replication. Ritonavir has negligible activity against SARS-CoV-2 at the dose used here; it is a strong CYP3A4 inhibitor included solely to reduce nirmatrelvir's hepatic metabolism, raising and prolonging its plasma concentration to maintain antiviral efficacy across the twice-daily dosing interval. (1)

What nirmatrelvir and ritonavir is used for

Mild-to-moderate COVID-19 in people at high risk of severe disease

Used to treat COVID-19 in adults (and, in some countries, adolescents from around age 12 weighing at least 40 kg) who do not need supplemental oxygen but are at increased risk of the illness progressing to hospitalisation or death. It is not authorised to prevent COVID-19 before or after an exposure, and is not intended for use for longer than 5 days. (1) (3) (5)

Before taking nirmatrelvir and ritonavir

Do not take / not appropriate for

  • Do not take Paxlovid if you have had a serious allergic reaction to nirmatrelvir, ritonavir, or any of the ingredients. (all countries) (1) (6)
  • Paxlovid is contraindicated in people with severe liver impairment -- there is not enough safety data to support its use in this group. (all countries) (1) (6)
  • Paxlovid must not be taken together with a range of specific medicines (see the Interactions section below) where the interaction risk is considered too dangerous to manage with monitoring alone. Your prescriber or pharmacist will check your full medicine list against this before you start. (all countries) (1) (2) (6)

Tell your clinician about

  • Every prescription medicine, over-the-counter medicine, herbal product, and supplement you currently take -- this is essential given the extensive interaction list.
  • Any liver or kidney problems, since both can change how Paxlovid should be dosed or whether it can be used at all.
  • Whether you have HIV infection that is untreated, undiagnosed, or not well controlled.
  • Whether you use hormonal contraception -- an additional non-hormonal method is recommended during and shortly after treatment.
  • Pregnancy, plans for pregnancy, or breastfeeding.
(1) (2)

How to take nirmatrelvir and ritonavir

  • Each dose is 3 tablets taken together: two 150 mg nirmatrelvir tablets and one 100 mg ritonavir tablet.
  • Taken twice a day (morning and evening) for 5 days in a row.
  • Swallow tablets whole -- do not chew, break, or crush them.
  • Can be taken with or without food.
  • Start as soon as possible after a positive COVID-19 test, and within 5 days of symptoms beginning.
  • Complete the full 5-day course as prescribed, even if you start feeling better, unless your prescriber advises otherwise.
(1)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (3) (2) (4) (5) (6)

Missed dose

If you miss a dose and it has been less than 8 hours since it was due, take it as soon as you remember. If more than 8 hours have passed, skip that dose and take your next dose at its regular scheduled time -- do not take a double dose.

Overdose

Seek urgent medical attention if you think you have taken too much Paxlovid, or if you develop severe or unusual symptoms. (1)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Altered or metallic taste (dysgeusia) -- the most common side effect.

What to notice: Altered or metallic taste (dysgeusia) -- the most common side effect.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1) (2)

Diarrhoea.

What to notice: Diarrhoea.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1) (2)

Headache and raised blood pressure.

What to notice: Headache and raised blood pressure.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Nausea, vomiting, and abdominal pain.

What to notice: Nausea, vomiting, and abdominal pain.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

A general feeling of being unwell (malaise).

What to notice: A general feeling of being unwell (malaise).

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Serious warnings

Serious drug interactions from ritonavir's effect on other medicines — boxed_warning

Symptoms: Symptoms vary widely depending on which interacting medicine is involved -- for example unusual bleeding (with certain blood thinners), extreme drowsiness or slowed breathing (with certain sedatives), or an irregular heartbeat (with certain heart-rhythm medicines).

Action: Before starting, your prescriber or pharmacist will check every medicine you take against the known interaction list and decide whether anything needs to be paused, dose-adjusted, or watched closely during your 5-day course. Do not start or stop any other medicine on your own during treatment -- always check with your prescriber or pharmacist first. (1) (4)

Signs of a serious allergic or severe skin reaction — emergency

Symptoms: Swelling of the face, lips, tongue, or throat; difficulty breathing; widespread rash, blistering, or peeling skin.

Action: Seek emergency medical help immediately. Your prescriber will decide whether to stop Paxlovid if a serious allergic or skin reaction occurs. (1) (2)

Signs of liver problems — high caution

Symptoms: Yellowing of the skin or eyes, dark urine, unusual tiredness, or loss of appetite.

Action: Contact your prescriber promptly, especially if you have a history of liver disease. (1)

Interactions

  • These must not be taken together with Paxlovid without your prescriber's involvement -- combining them can raise the heart medicine to dangerous levels and cause serious heart rhythm problems. Do not take together without checking with your prescriber or pharmacist first. (1) (2) (6)
  • These specific statins are not to be combined with Paxlovid due to a serious risk of muscle breakdown (rhabdomyolysis). Your prescriber may advise pausing the statin for the duration of treatment and for some days afterward. Do not take together without checking with your prescriber or pharmacist first. (1) (2)
  • Combining these with Paxlovid can cause dangerous restriction of blood flow to the hands, feet, or other tissues (ergot toxicity). Do not take together without checking with your prescriber or pharmacist first. (1) (6)
  • These can build up to levels causing extreme sleepiness and dangerously slowed breathing when combined with Paxlovid. Do not take together without checking with your prescriber or pharmacist first. (1) (2)
  • These carry a serious interaction risk with Paxlovid, including toxicity that can affect the heart, blood vessels, or muscles. Do not take together without checking with your prescriber or pharmacist first. (1) (6)
  • Combining these with Paxlovid can raise the antipsychotic medicine to levels that risk serious heart rhythm problems. Do not take together without checking with your prescriber or pharmacist first. (1) (2) (6)
  • These can interact with Paxlovid in ways that risk very low blood pressure, an abnormal heart rhythm, or dangerous changes in body salt/fluid balance. Do not take together without checking with your prescriber or pharmacist first. (1) (2)
  • These require very close level monitoring if combined with Paxlovid, and are best avoided unless that close monitoring is realistically possible -- levels can rise sharply and affect the kidneys. Do not take together without checking with your prescriber or pharmacist first, ideally involving the transplant team. (1)
  • Paxlovid can increase bleeding risk with these medicines. Your prescriber may want extra monitoring (such as more frequent INR checks for warfarin) or a temporary dose change during your 5-day course. Do not take together without checking with your prescriber or pharmacist first. (1)
  • Paxlovid can increase opioid levels, raising the risk of slowed or stopped breathing. Your prescriber may recommend closer monitoring or a temporary dose adjustment. Do not take together without checking with your prescriber or pharmacist first. (1)
  • Levels of these medicines can rise during Paxlovid treatment. Your prescriber may want to monitor you more closely or temporarily reduce the dose. Do not take together without checking with your prescriber or pharmacist first. (1)
  • These medicines can lower Paxlovid's levels enough to risk the treatment not working properly and the virus becoming resistant. Paxlovid cannot be started right after stopping one of these, because the effect lingers -- your prescriber will need to plan around this. Do not take together without checking with your prescriber or pharmacist first. (1) (2) (6)
  • Paxlovid can reduce how well hormonal contraception works. Use an additional non-hormonal method (such as condoms) during treatment and for one full menstrual cycle after finishing Paxlovid. (1) (2)
  • This list covers the main interaction categories but is not exhaustive. Because ritonavir affects so many other medicines, always give your prescriber or pharmacist your complete, current medicine list -- including over-the-counter products, herbal remedies, and supplements -- before starting Paxlovid, and do not add or stop any medicine yourself during the 5-day course without checking first. (1) (6)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

There is limited human data on nirmatrelvir in pregnancy, though ritonavir has extensive safety data from HIV-treatment pregnancy registries without a clear increase in birth defects. Untreated COVID-19 during pregnancy carries its own risks. Use is generally considered only if the expected benefit outweighs the uncertain risk -- discuss your individual situation with your prescriber. (1) (3) (2) (4) (5) (6)

Breastfeeding

Small amounts of both components pass into breast milk. Many prescribers advise pausing breastfeeding during treatment and for a short period after the last dose -- follow your prescriber's specific guidance for your situation. (1) (3) (2) (4) (5) (6)

Children

Approved in some countries (including the EU) from around age 6-12 (weighing at least 40 kg) under specific authorisations; in the US this age group is covered under an Emergency Use Authorization rather than full approval. Age and weight thresholds vary by country -- confirm with your prescriber. (1) (3) (2) (4) (5) (6)

Elderly

No specific age-based dose adjustment beyond the standard kidney-function-based adjustments, which become more relevant as kidney function commonly declines with age. (1) (3) (2) (4) (5) (6)

Hepatic_impairment

No adjustment needed for mild or moderate liver impairment. Contraindicated in severe liver impairment due to insufficient safety data. (1) (3) (2) (4) (5) (6)

Renal_impairment

No adjustment for mild kidney impairment. Reduced dose for moderate impairment. Further-reduced regimen for severe impairment, including in people on haemodialysis (dosed after a dialysis session on dialysis days). (1) (3) (2) (4) (5) (6)

Source_ids

US-DAILYMED-PAXLOVID-2026,UK-EMC-PAXLOVID-2026,NZ-MEDSAFE-PAXLOVID-2026 (1) (3) (2) (4) (5) (6)

Monitoring

Before starting

  • Full, current medicine list review for CYP3A interactions
  • Kidney function (eGFR)
  • Liver function/history of liver disease
  • HIV status, if relevant and unknown

During treatment

  • Watching for signs of an interacting medicine building up (varies by which medicine is involved).
  • Watching for signs of an allergic or serious skin reaction.
  • Watching for signs of liver problems, particularly in people with pre-existing liver disease.
(1)

Storage

Store at room temperature, below 25°C (77°F), in the original packaging. Keep the tablets in their blister pack until it is time to take them.

Professional information

Clinician-facing context only, sourced from the current US FDA prescribing information and the New Zealand Medsafe data sheet; verify against the current full label and a dedicated interaction-checking resource before prescribing.

United States / New Zealand

Indication: Mild-to-moderate COVID-19, high-risk adults (and adolescents under regional authorisation)

Dose summary: Standard: 300 mg nirmatrelvir + 100 mg ritonavir orally twice daily for 5 days, started within 5 days of symptom onset. Renal: eGFR 60-<90 no change; eGFR 30-<60 reduce to 150mg+100mg twice daily; eGFR <30 (including haemodialysis) 300mg+100mg once on Day 1 then 150mg+100mg once daily Days 2-5, dosed after haemodialysis on dialysis days. Hepatic: no change for Child-Pugh A/B; contraindicated for Child-Pugh C.

Renal context: See dose_summary -- renal impairment is a primary driver of dose adjustment for this medicine. (1) (6)

Mechanism of action

Hepatic guidance

Contraindicated in severe hepatic impairment (Child-Pugh C) due to insufficient pharmacokinetic and safety data; no adjustment needed for Child-Pugh A/B.

Overdose note

No specific antidote. Manage supportively, with attention to the possibility of concurrent interacting-medicine toxicity depending on the patient's other medicines. (1)

Frequently asked questions

Is Paxlovid (nirmatrelvir/ritonavir) available in the US, UK, Europe, Canada, Australia, and New Zealand?

Yes, it is authorised in all of these regions, though the exact approval pathway differs -- for example, it has full FDA approval for adults in the US (since 2023) alongside an ongoing Emergency Use Authorization for adolescents, while several other regions use a conditional or provisional approval. (1) (3) (2) (4) (5) (6)

Why does Paxlovid interact with so many other medicines?

One of its two components, ritonavir, strongly blocks a liver enzyme (CYP3A) that many other medicines rely on to be broken down and cleared from the body. Blocking this enzyme is intentional -- it's what keeps the antiviral component, nirmatrelvir, at effective levels -- but it also means many other medicines can build up to unsafe levels if taken at the same time. This is why a full medicine review before starting is essential. (1)

Can I take my regular medicines while on Paxlovid?

Possibly, but this needs to be checked individually. Some medicines cannot be combined with Paxlovid at all; others can be continued with a temporary dose change or extra monitoring; others need to be paused for the 5-day course. Never make this decision yourself -- always check with your prescriber or pharmacist before starting Paxlovid or changing anything about your other medicines. (1)

What is COVID-19 rebound, and does it mean Paxlovid failed?

Some people notice symptoms or a positive test again a few days after finishing Paxlovid (or after having COVID-19 untreated). This has been seen in both Paxlovid recipients and people who did not take it, and has not been linked to worse outcomes in studies so far, but its overall significance is still being studied. If you have concerns about recurring symptoms, contact your prescriber. (1)

What is the mechanism of action of nirmatrelvir and ritonavir?

Nirmatrelvir is a peptidomimetic inhibitor of the SARS-CoV-2 main protease (Mpro, also called 3CL protease), an enzyme required for viral replication. Ritonavir has negligible activity against SARS-CoV-2 at the dose used here; it is a strong CYP3A4 inhibitor included solely to reduce nirmatrelvir's hepatic metabolism, raising and prolonging its plasma concentration to maintain antiviral efficacy across the twice-daily dosing interval. (1)

What is the generic name of Nirmatrelvir/ritonavir?

The generic name is nirmatrelvir and ritonavir. (1)

What class of drug is nirmatrelvir and ritonavir?

Nirmatrelvir/ritonavir is classed as: Oral antiviral combination -- SARS-CoV-2 main protease inhibitor (nirmatrelvir) plus a pharmacokinetic-boosting CYP3A inhibitor (ritonavir). (1)

References

  1. PAXLOVID (nirmatrelvir tablets; ritonavir tablets) -- full prescribing informationU.S. Food and Drug Administration / DailyMed (NIH), full prescribing information, Pfizer Laboratories Div Pfizer Inc. · United States · accessed 2026-07-29 · source 1
  2. Paxlovid 150 mg/100 mg film-coated tablets -- Summary of Product Characteristicselectronic medicines compendium (emc), United Kingdom -- Pfizer Limited · United Kingdom · accessed 2026-07-29 · source 2
  3. Paxlovid European Public Assessment Report (EPAR) and product informationEuropean Medicines Agency (EMA) · European Union · accessed 2026-07-29 · source 3
  4. PAXLOVID (nirmatrelvir; ritonavir) Product MonographHealth Canada product monograph · Canada · accessed 2026-07-29 · source 4
  5. PAXLOVID nirmatrelvir/ritonavir -- ARTG registration and Product InformationTherapeutic Goods Administration (TGA), Australia · Australia · accessed 2026-07-29 · source 5
  6. PAXLOVID New Zealand Data SheetMedsafe (New Zealand regulator) · New Zealand · accessed 2026-07-29 · source 6

Brand names by country

Single-ingredient nirmatrelvir and ritonavir names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • Paxlovid (1)FDA full NDA approval 2023 for adults EUA active for adolescents 12to17 over 40kg · 150 mg nirmatrelvir tablet / 100 mg ritonavir tablet, co-packaged · Pfizer Laboratories Div Pfizer Inc.

United Kingdom

  • Paxlovid (2)MHRA licensed emc smpc confirmed additional monitoring black triangle · 150 mg / 100 mg · Pfizer Limited

Canada

  • Paxlovid (4)Health Canada approved confirmed · 150 mg / 100 mg · Pfizer Canada ULC

Australia

  • Paxlovid (5)TGA ARTG registered confirmed provisional approval 2022-01-18 · 150 mg / 100 mg · Pfizer Australia Pty Ltd

New Zealand

  • Paxlovid (6)Medsafe approved confirmed data sheet extracted directly · 150 mg / 100 mg · Pfizer New Zealand Limited
View brands in additional countries.

European Union

Paxlovid (3)