Paxlovid

Pronunciation: pax-LO-vid
Generic name: nirmatrelvir and ritonavir
Dosage form: tablets, co-packaged for oral use
Drug class: Antiviral combinations

Medically reviewed by Melisa Puckey, BPharm. Last updated on Apr 2, 2024.

What is Paxlovid?

Paxlovid is an antiviral medication used to treat COVID-19 to help decrease symptoms or avoid severe illness in certain patients. Paxlovid works by stopping the virus that causes COVID-19 (SARS-CoV-2) from multiplying. Paxlovid should be taken as soon as possible after diagnosis of COVID-19.  Paxlovid contains two medications called nirmatrelvir (pink tablets) and ritonavir (white tablets). 

Paxlovid may be prescribed for an individual patient by physicians, advanced practice registered nurses, and physician assistants licensed or authorized under state law to prescribe drugs. It may also be prescribed for an individual patient by a state-licensed pharmacist under specific conditions.

Is Paxlovid FDA approved?

Yes, Paxlovid is an FDA-approved medicine; it was FDA-approved on May 25, 2023. Paxlovid is used 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.

Paxlovid is also available under an Emergency Use Authorisation (EUA) to treat patients 12 to 18 years old for mild-to-moderate COVID-19 who are at high risk for progression to severe COVID-19, including hospitalization or death.

Paxlovid is not approved for use as pre-exposure or post-exposure prophylaxis for the prevention of COVID-19 or prevention of Long COVID.

Paxlovid side effects

Common Paxlovid side effects 

Common Paxlovid side effects include a bad taste or change in taste, diarrhea, headache, vomiting, stomach pain, nausea, or high blood pressure.

Serious Paxlovid side effects

Get emergency medical help if you have signs of an allergic reaction (hives, difficulty breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Call your doctor at once if you have:

• liver problems symptoms include loss of appetite, stomach pain (upper right side), tiredness, itching, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Ritonavir affects your immune system, which may cause certain side effects (even weeks or months after you've taken nirmatrelvir and ritonavir). Tell your doctor if you have:

• signs of a new infection--fever, night sweats, swollen glands, cold sores, cough, wheezing, diarrhea, weight loss;
• trouble speaking or swallowing, problems with balance or eye movement, weakness or prickly feeling; or
• swelling in your neck or throat (enlarged thyroid), menstrual changes, impotence.

This is not a complete list of side effects, and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Related/similar drugs

Lagevrio, molnupiravir, remdesivir, Actemra, nirmatrelvir / ritonavir, Olumiant

Paxlovid rebound and COVID-19 rebound

COVID-19 rebound is when COVID-19 symptoms return between 2 and 8 days after initial COVID-19 recovery, this can happen in some people that are in vaccinated, unvaccinated, Paxlovid treated and people who have not been treated with Paxlovid. When COVID-19 symptoms return in Paxlovid treated patients, some people have called it Paxlovid rebound.

The CDC states that “There is currently no evidence that additional treatment is needed with Paxlovid or other anti-SARS-CoV-2 therapies in cases where COVID-19 rebound is suspected.”

How does Paxlovid work?

Paxlovid works as nirmatrelvir, is an antiviral medication that stops the virus from multiplying. Nirmatrelvir is a SARS-CoV-2 main protease (Mpro) inhibitor (also known as SARS-CoV2 3CL protease inhibitor) that works by inhibiting viral replication in the early stages of the disease to prevent progression to severe COVID-19.

Ritonavir is taken with nirmatrelvir to help slow the metabolism of nirmatrelvir so that it stays in the body for longer periods of time at higher concentrations to help combat the virus.

Before taking this medicine

You should not use Paxlovid if you are allergic to the active ingredients nirmatrelvir and ritonavir, or any of the inactive ingredients. Click here for a full list of Paxlovid ingredients. 

Some drugs have drug interactions with Paxlovid, and they should not be used with Paxlovid, such as those listed below.

• alfuzosin, colchicine;
• sildenafil (Revatio) when used to treat pulmonary arterial hypertension (PAH);
• pain medicine - pethidine, piroxicam, propoxyphene;
• heart medicine - amiodarone, dronedarone, flecainide, propafenone, quinidine, ranolazine;
• antipsychotic medicine - lurasidone, pimozide, clozapine;
• ergot medicine - dihydroergotamine, ergotamine, methylergonovine;
• cholesterol-lowering medicine - lovastatin, simvastatin; or
• a sedative - riazolam, oral midazolam.

Paxlovid should not be started immediately after discontinuation of any of the following drugs:

• rifampin;
• St. John's Wort;
• a cancer medicine - apalutamide; or
• seizure medicine - carbamazepine, phenobarbital, phenytoin.

Also, see the Interactions section below.

Tell your doctor if:

• you have liver problems or a liver disease such as hepatitis;
• you have kidney problems;
• you have an HIV-1 infection;
• you are pregnant or breastfeeding; or
• you have any serious or chronic disease.

Pregnancy 

Tell your healthcare provider right away if you are or if you become pregnant. It is not known if Paxlovid can harm your unborn baby. Ritonavir can make birth control pills or birth control skin patches less effective. Ask your doctor about other birth control options such as an injection, implant, vaginal ring, condom, diaphragm, cervical cap, or contraceptive sponge.

Breastfeeding

Tell your healthcare provider are breastfeeding or plan to breastfeed. It is not known if Paxlovid can pass into your breast milk. Talk to your healthcare provider about the best way to feed your baby during treatment with this medicine.

How should I take Paxlovid?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Paxlovid Instructions

Take nirmatrelvir together with ritonavir (two tablets of nirmatrelvir and one tablet of ritonavir) twice a day for 5 consecutive days. If you have kidney disease, talk to your healthcare provider, as you may need to take a different dose.

Take Paxlovid as soon as possible after diagnosis of COVID-19 and within 5 days of when symptoms first appear.

You may take Paxlovid with or without food.

Swallow the tablets whole and do not crush, chew, or break them.

General Information

You may need frequent blood tests to check your liver function.

If you are taking a ritonavir- or cobicistat-containing medicine to treat hepatitis C or Human Immunodeficiency Virus (HIV), you should continue to take your medicine as prescribed by your healthcare provider.

Talk to your healthcare provider if you do not feel better or if you feel worse after 5 days.

If you have kidney disease, your prescriber may prescribe you a lower dose. Talk to
your healthcare provider to make sure you receive the correct Dose Pack.

Paxlovid Dosage information

Usual Paxlovid Dosing for Adult COVID-19 (FDA-approved)

Nirmatrelvir: 300 mg orally twice a day
Ritonavir: 100 mg orally twice a day
Duration of therapy: 5 days
Comments:

• If you have kidney disease, your healthcare provider may prescribe a lower dose. Talk to your healthcare provider to ensure you receive the correct Dose Pack.

• Nirmatrelvir must be taken together with ritonavir; the dosage consists of 3 tablets (2 nirmatrelvir 150-mg tablets and 1 ritonavir 100-mg tablet), and all 3 of those tablets should be taken together. Prescriptions should specify the numeric dose of each active component within this product.
• This product should be started as soon as possible after COVID-19 has been diagnosed and within 5 days of symptom onset.
• If hospitalization is required due to severe/critical COVID-19 after starting treatment with this product, the patient should complete the full 5-day treatment course per health care provider's discretion.

Use: For the treatment of mild to moderate COVID-19 in adults who are at high risk for progression to severe COVID-19, including hospitalization or death.

Usual Paxlovid Dosing for 12 to 18 Year Old COVID-19 (EUA)

For investigational use only
Use: Patients 12 to 18 years old weighing at least 40 kg:
Nirmatrlvir: 300 mg orally twice a day
Ritonavir: 100 mg orally twice a day
Duration of therapy: 5 days
Comments:

• If you have kidney disease, your healthcare provider may prescribe a lower dose. Talk to your healthcare provider to make sure you receive the correct Dose Pack.
• The US FDA issued an EUA to allow the emergency use of the unapproved product, nirmatrelvir co-packaged with ritonavir, for the treatment of mild to moderate COVID-19 in are at high risk for progression to severe COVID-19, including hospitalization or death; this product is not approved by the US FDA for this use.
• Nirmatrelvir must be coadministered with ritonavir; the dosage consists of 3 tablets (2 nirmatrelvir 150-mg tablets and 1 ritonavir 100-mg tablet), and all 3 of those tablets should be administered together. Prescriptions should specify the numeric dose of each active component within this product.
• This product should be started as soon as possible after COVID-19 has been diagnosed and within 5 days of symptom onset.
• If hospitalization is required due to severe/critical COVID-19 after starting treatment with this product, the patient should complete the full 5-day treatment course per health care provider's discretion.

What happens if I miss a dose?

If you miss a dose of Paxlovid within 8 hours of the time it is usually taken, take it as soon as you remember. If you miss a dose by more than 8 hours, skip the missed dose and take the next dose at your regular time. Do not take 2 doses of Paxlovid at the same time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What other drugs will affect Paxlovid?

Sometimes it is not safe to use certain medicines at the same time. Some drugs can affect your blood levels of other drugs you use, which may increase side effects or make the medicines less effective.

Many drugs can affect Paxlovid and some drugs should not be used at the same time. Paxlovid can interact with other medicines causing severe or life-threatening side effects or death. Tell your doctor about all other medicines you use. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. 

Paxlovid Drug Interactions

Do not take Paxlovid  if you are taking any of the following medicines: alfuzosin, amiodarone, apalutamide, carbamazepine, colchicine, dihydroergotamine, dronedarone, eletriptan, eplerenone, ergotamine, finerenone, flecainide, flibanserin, ivabradine, lomitapide, lovastatin, lumacaftor/ivacaftor, lurasidone, methylergonovine, midazolam (oral), naloxegol, phenobarbital, phenytoin, pimozide, primidone, propafenone, quinidine, ranolazine, rifampin, rifapentine, St. John’s Wort (hypericum perforatum), sildenafil (Revatio®, Liqrev®) for pulmonary arterial hypertension, silodosin, simvastatin, tolvaptan,  triazolam, ubrogepant, voclosporin.

These are not the only medicines that may cause serious or life-threatening side effects if taken with Paxlovid. It is very important to tell your healthcare provider about all of the medicines you are taking because additional laboratory tests or changes in the dose of your other medicines may be necessary during treatment with this Paxlovid. Your healthcare provider may also tell you about specific symptoms to watch out for that may indicate that you need to stop or decrease the dose of some of your other medicines.

To check for interactions with Paxlovid click on the link below.

Ingredients

Nirmatrelvir 150 mg tablets

Active ingredient: nirmatrelvir
Inactive ingredients: colloidal silicon dioxide, croscarmellose sodium, lactose monohydrate, microcrystalline cellulose, and sodium stearyl fumarate. The following are the ingredients in the film coating: hydroxy propyl methylcellulose, iron oxide red, polyethylene glycol, and titanium dioxide.

Ritonavir 100 mg tablets

Active ingredient: ritonavir
Inactive ingredients: anhydrous dibasic calcium phosphate, colloidal silicon dioxide, copovidone, sodium stearyl fumarate, and sorbitan monolaurate. The following are the ingredients in the film coating: colloidal silicon dioxide, hydroxypropyl cellulose, hypromellose, polyethylene glycol 400, polyethylene glycol 3350, polysorbate 80, talc, and titanium dioxide.

Storage

Store at room temperature temperature 20°C to 25°C (68°F to 77°F).

Company 

Distributed by Pfizer Labs, Division of Pfizer Inc. New York, NY 10001.

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