Paxlovid is a medication used to treat coronavirus disease 2019 (COVID-19) (1). Paxlovid reduces the risk of progression to severe COVID-19 by 89% compared to placebo, “without evident safety concerns,” a recent study shows. (2)
Paxlovid is a combination of two antiviral medications, nirmatrelvir and ritonavir. The most common side effects of Paxlovid are a change in taste, diarrhea, muscle pain, and high blood pressure. These side effects are usually mild and go away on their own. However, some people may experience more serious side effects, such as severe allergic reactions. Severe allergic reactions can be life-threatening and require immediate medical attention. (1)
Continue reading this article to learn more about the side effects that this effective medication may cause. In addition, you can learn about the known side effects reported in studies and real-life data and when you should call your doctor.
Paxlovid Known Side Effects
If you are positive for COVID-19 and at high risk for disease progression or hospitalization, then you are eligible for Paxlovid treatment. Your doctor may prescribe Paxlovid and give you the Fact sheet for patients, parents, and caregivers. (3)
Read the Fact sheet carefully when taking Paxlovid. Paxlovid may cause the following side effects, which have been reported in clinical studies: (1)
- Altered sense of taste (6%);
- Diarrhea (3%);
- High blood pressure (1%);
- Muscle aches (1%).
Paxlovid users also have reported abdominal pain, nausea, hypersensitive reactions, anaphylaxis, and malaise (a feeling of discomfort, illness, or lack of well-being). (1, 3)
Allergic Reaction To Paxlovid
Some people may be allergic to Paxlovid and its active ingredients or the other components; if you are one, you shouldn’t use Paxlovid. The symptoms of allergic reaction that can appear soon after taking the first dose are: (3)
- Trouble swallowing or breathing;
- Swelling of the mouth, lips, tongue, or face;
- Throat tightness;
- Skin rash.
If you notice any of these symptoms, stop taking the drug and call your doctor immediately. (1, 3)
Reporting Side Effects
All side effects of Paxlovid are not yet known. Paxlovid has a narrow indication for use; therefore, few patients have been treated and reported side effects. If you take Paxlovid, inform your doctor of any adverse reaction you experience that bothers you and doesn’t go away. (3)
You can report adverse reactions to FDA MedWatch at www.fda.gov/medwatch or call 1-800-FDA-1088, or you can report it to the manufacturer, Pfizer Inc. It will help health authorities to evaluate all serious and unexpected side effects and their frequency. (3)
Paxlovid: Warnings And Precautions
Paxlovid may cause serious side effects, as described in the Fact Sheet for Patients, Parents, and Caregivers. Patients with previous liver disease who have hepatitis or enzyme abnormalities should use Paxlovid with caution due to potential liver toxicity. (3)
You should also be aware of the following potential life-threatening situations:
Paxlovid interacts with some medications metabolized by the CYP3A pathway in the human body. (1) CYP3A is cytochrome P450, a protein in the liver and gastrointestinal tract that plays an essential role in drug metabolism. (4-5)
Paxlovid inhibits CYP3A, so if given a medication whose metabolism depends on CYP3A, it may increase concentrations of that medication and its side effects. If the medication inhibits or induces CYP3A, it will affect Paxlovid concentrations in the body. (1)
Such drug interaction may lead to a lost therapeutic effect of Paxlovid and virus resistance, adverse reactions due to higher Paxlovid concentration, and severe, life-threatening, or even fatal adverse reactions (1). Tell your doctor or pharmacist all the medications you already take to avoid any interaction and complications.
Paxlovid can interact with certain medications, which can cause serious or life-threatening side effects or make Paxlovid less effective. The Fact sheet lists all of the medications that can interact with Paxlovid. If you take any of these medications, you should not take Paxlovid.
Here are some specific examples of medications that can interact with Paxlovid:
If you are taking any of these medications, you should talk to your doctor before taking Paxlovid. Your doctor can help you determine if Paxlovid is right for you and can recommend alternative medications if necessary.
A severe allergic and life-threatening reaction has been reported by some patients using Paxlovid. (1, 3) A rapid or weak pulse, skin rash, nausea, and vomiting are signs and symptoms of an anaphylactic reaction requiring emergency care. (6)
Stevens-Johnson Syndrome (SJS)
Ritonavir, one of the active ingredients in Paxlovid, has been linked to cases of Stevens-Johnson syndrome (SJS). This is a rare side effect of some medications that affect the skin. (1, 7)
In the beginning, people with SJS may experience flu-like symptoms such as fever, sore throat, fatigue, and burning eyes. These symptoms are followed by a painful skin rash that spreads and forms blisters. The damaged skin then dies.
A more severe form of SJS is called toxic epidermal necrolysis (TEN). In TEN, over 30% of the skin is affected. (8)
It is important to note that the risk of developing SJS or TEN is very low. However, if you experience any of the symptoms of these conditions, it is important to seek medical attention immediately.
Liver toxicity is a rare side effect of Paxlovid, but it can cause liver problems. If you experience any of the following symptoms, tell your healthcare provider right away:
Yellowing of the skin or the whites of the eyes;
- Dark-colored urine;
- Pale-colored stools;
- Loss of appetite;
- Itchy skin;
- Pain in the stomach.
Resistance To HIV Medicines
Paxlovid may reduce the effectiveness of some HIV medications in people who have untreated HIV infection. If you have untreated HIV infection, you should not take Paxlovid unless you are also taking HIV medications.
When Can Paxlovid Be Used?
Paxlovid is used to treat mild-to-moderate COVID-19 in adults and children older than 12 years who are at least 40 kg in weight. The doctor can prescribe Paxlovid only to a patient with positive SARS-CoV-2 viral test results and who has a high risk of the disease progressing to severe COVID-19, including hospitalization or death. (1, 3)
Paxlovid is a combination of two drugs:
- Nirmatrelvir – SARS-CoV-2 main protease inhibitor, and
- Ritonavir – HIV-1 protease inhibitor and CYP3A inhibitor. (1)
Nirmatrelvir inhibits the enzyme necessary for COVID virus replication to grow and spread in the body. In the early stage of the disease, thanks to nirmatrelvir, the COVID virus is disabled to enter and infect cells, so the infection is stopped. (1)
Ritonavir is a medication previously used for the treatment of HIV infection. The role of ritonavir in COVID infection is to inhibit CYP3A, which mediates nirmatrelvir metabolism. In that way, nirmatrelvir is available in the body longer and can fight the COVID infection more than on its own. (1)
Paxlovid cannot be used to prevent COVID-19 before or after the individual has been exposed to it. Paxlovid is not approved for use in those who have severe COVID-19 or are critical and need hospitalization (1, 3).
Those who have severe renal or hepatic impairment should not take Paxlovid. (1, 3)
How Should You Take Paxlovid?
Paxlovid pack contains 20 pink tablets of 150 mg nirmatrelvir and 10 white tablets of 100 mg ritonavir. The therapy should be initiated after diagnosis of COVID-19 and within five days of the occurrence of the symptoms. (1)
Take two nirmatrelvir tablets and one ritonavir tablet at the same time, in the morning and the evening. Use Paxlovid for five days in a row and complete the course. Don’t stop taking Paxlovid earlier than completing the five days’ therapy, even if you feel better. (1)
If you miss the dose, take it as soon as possible, and don’t double the dose to make up for the missed one. If you are late for more than eight hours, wait until the time for the other dose comes. (1)
Final thoughts Side Effects Of Paxlovid
Paxlovid has been shown to be highly effective in reducing the risk of disease progression and hospitalization in patients with COVID-19. This was most evident when Paxlovid was given within the first five days of symptom onset.
The side effects of Paxlovid are described in the drug’s Fact Sheet. While some side effects are mild and may not cause any problems, others, such as allergic reactions, drug interactions, or liver problems, can be severe and life-threatening. If you experience any of the symptoms described in the Fact Sheet, call your doctor immediately.
Not all severe and unexpected side effects are known so far. Therefore, it is important to recognize any of the described side effects or changes that appear and report them to the doctor, FDA, and manufacturer.
Take Paxlovid following your doctor’s instructions and stay home according to the latest recommendations.
- FDA Food and Drug Administration, Fact Sheet for Healthcare Providers, 2022 Sep, https://www.fda.gov/media/155050/download
- CDC Centers for Disease Control and Prevention, COVID Data Tracker, 2023 Jan, https://covid.cdc.gov/covid-data-tracker/#datatracker-home
- J. Hammond, Ph.D., H. Leister-Tebbe, B.S.N., A. Gardner, M.P.H., et al., Oral Nirmatrelvir for High-Risk, Nonhospitalized Adults with Covid-19, N Engl J Med 2022 Apr; 386:1397-1408 https://www.nejm.org/doi/full/10.1056/NEJMoa2118542
- FDA Food and Drug Administration, Fact Sheet for Patients, Parents, and Caregivers, 2022 Sep, https://www.fda.gov/media/155051/download
- G.R. Wilkinson, Cytochrome P4503A (CYP3A) metabolism: prediction of in vivo activity in humans, J Pharmacokinet Biopharm. 1996 Oct;24(5):475-90. https://pubmed.ncbi.nlm.nih.gov/9131486/
- A.M. McDonnell and C.H. Dang, Basic Review of the Cytochrome P450 System, J Adv Pract Oncol. 2013 Jul-Aug; 4(4): 263–268. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4093435/
- Mayo Clinic, Anaphylaxis, 2021 Oct, https://www.mayoclinic.org/diseases-conditions/anaphylaxis/symptoms-causes/syc-20351468#:~:text=Anaphylaxis%20is%20a%20severe%2C%20potentially,as%20peanuts%20or%20bee%20stings.
- FDA, NORVIR (ritonavir) Prescribing information, 2017 Jun, https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/209512lbl.pdf
- Mayo Clinic, Stevens-Johnson syndrome, 2023 Jan, https://www.mayoclinic.org/diseases-conditions/stevens-johnson-syndrome/symptoms-causes/syc-20355936#:~:text=Stevens%2DJohnson%20syndrome%20(SJS),to%20heal%20after%20several%20days.
- FDA Food and Drug Administration, Emergency Use Authorization, 2023 Jan, https://www.fda.gov/emergency-preparedness-and-response/mcm-legal-regulatory-and-policy-framework/emergency-use-authorization