How does this medication work? What will it do for me?

Nirmatrelvir-ritonavir is a combination treatment that belongs to the class of medications called antivirals. It is used to treat mild-to-moderate COVID-19 infection in adults who are at high risk of developing severe COVID-19, including hospitalization or death.

This medication is not approved for prevention of COVID-19 infections or for treatment of people who are hospitalized with a severe COVID-19 infection. It should not be used for more than 5 days in a row.

Nirmatrelvir works by blocking the action of a protease enzyme that the COVID-19 virus needs to reproduce. 

Ritonavir is also a protease inhibitor, however it is not active against the COVID-19 virus. Instead, it enhances the action of nirmatrelvir by slowing the breakdown of nirmatrelvir and removal from the body. By this method, it increases the amount and length of time that nirmatrelvir is active in the body.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

What form(s) does this medication come in?

Nirmatrelvir

Each oval, pink, immediate-release, film-coated tablet, debossed with "PFE" on one side and "3CL" on the other side, contains 150 mg of nirmatrelvir. Nonmedicinal ingredients: colloidal silicon dioxide, croscarmellose sodium, lactose monohydrate, microcrystalline cellulose, and sodium stearyl fumarate; Film coat: hydroxy propyl methylcellulose, iron oxide red, polyethylene glycol and titanium dioxide.

Ritonavir

Each white, film-coated, ovaloid tablet, debossed with the "a" logo and the code NK, contains 100 mg of ritonavir. Nonmedicinal ingredients: anhydrous dibasic calcium phosphate, colloidal silicon dioxide, copovidone, sodium stearyl fumarate, and sorbitan monolaurate; Film coat: colloidal silicon dioxide, hydroxypropyl cellulose, hypromellose, polyethylene glycol 400, polyethylene glycol 3350, polysorbate 80, talc and titanium dioxide.

How should I use this medication?

The dose of nirmatrelvir-ritonavir is 300 mg of nirmatrelvir (2 pink 150 mg tablets) and 100 mg of ritonavir (1 white 100 mg tablet). All 3 tablets are taken together by mouth at the same time, 2 times daily. If you have kidney problems, your doctor may recommend a lower dose.

 Nirmatrelvir-ritonavir should be started as soon as possible after a diagnosis of COVID-19 infection and is taken for a total of 5 days. Finish all this medication, even if you have started to feel better.

Nirmatrelvir-ritonavir may be taken with food or on an empty stomach. Swallow the tablets whole with some fluids. Do not crush, chew, or break the tablets.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor.

If you miss a dose and it is within 8 hours of the usual time you take it, take it as soon as possible and continue with your regular schedule. If you have missed the dose by more than 8 hours, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

Who should NOT take this medication?

Do not take this medication if you:

  • are allergic to nirmatrelvir, ritonavir, or any ingredients of the medication
  • are taking any of the following medications:
    • alfuzosin
    • anti-arrhythmic medications (medications to treat irregular heartbeat; e.g., amiodarone, dronedarone, flecainide, propafenone, quinidine)
    • apalutamide
    • certain cholesterol medications (e.g., lovastatin, simvastatin, lomitapide)
    • colchicine
    • ergot derivatives (e.g., dihydroergotamine, ergonovine, methyergonovine)
    • fusidic acid
    • lurasidone
    • midazolam
    • pimozide
    • ranolazine
    • rifampin
    • rivaroxaban
    • St. John's wort
    • salmeterol
    • seizure medications (e.g., carbamazepine, phenobarbital, phenytoin)
    • sildenafil
    • triazolam
    • vardenafil
    • venetoclax
    • voriconazole

What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • changed sense of taste
  • diarrhea
  • headache
  • muscle pain
  • vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • increased blood pressure

Stop taking the medication and seek immediate medical attention if any of the following occur:

  • signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
  • signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Kidney Function: Decreased kidney function or kidney disease causes nirmatrelvir to build up in the body, causing side effects. If you have kidney problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. This medication is not recommended for people with severely decreased kidney function.

Liver Function: The effect that decreased liver function has on this medication has not been studied. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Some people who have taken ritonavir have experienced decreased liver function. If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Women who may become pregnant should use a non-hormonal form of birth control such as condoms while taking nirmatrelvir-ritonavir.

Breast-feeding: It is not known if nirmatrelvir passes into breast milk. Ritonavir passes into breast milk in small amounts. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children.

What other drugs could interact with this medication?

There may be an interaction between nirmatrelvir-ritonavir and any of the following:

  • albendazole
  • aliskiren
  • alpha blockers (e.g., alfuzosin, doxazosin, silodosin, tamsulosin)
  • anticancer medications (e.g., cladribine, cyclophosphamide, docetaxel, etoposide, irinotecan, trabectedin, vincristine, vinblastine)
  • antihistamines (e.g., azelastine, cetirizine, doxylamine, diphenhydramine, hydroxyzine, ketotifen, loratadine, rupatadine)
  • antiarrhythmic medications (e.g., amiodarone, disopyramide, dronedarone, procainamide, quinidine, sotalol)
  • antipsychotics (e.g., chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
  • apalutamide
  • apixaban
  • aprepitant
  • atovaquone
  • "azole" antifungals (e.g., itraconazole, ketoconazole, voriconazole)
  • benzodiazepines (e.g., alprazolam, clonazepam, diazepam, midazolam, triazolam)
  • beta-2 agonists (e.g., salmeterol, vilanterol)
  • bictegravir
  • birth control pills (hormonal contraceptives)
  • bosentan
  • bromocriptine
  • bupropion
  • calcitriol
  • cannabis
  • calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
  • cinacalcet
  • clindamycin
  • clopidogrel
  • colchicine
  • conivaptan
  • corticosteroids (e.g., betamethasone, budesonide, dexamethasone, fluticasone, hydrocortisone, prednisone)
  • cyclosporine
  • darifenacin
  • deferasirox
  • desipramine
  • desvenlafaxine
  • diabetes medications (e.g., acarbose, canagliflozin, glyburide, insulin, linagliptin, lixisenatide, metformin, repaglinide, rosiglitazone)
  • digoxin
  • domperidone
  • dutasteride
  • edoxaban
  • elagolix
  • elexacaftor-tezacaftor-ivacaftor
  • eluxadoline
  • enzalutamide
  • eplerenone
  • ergot derivatives (e.g., dihydroergotamine, ergotamine)
  • estrogens (e.g., conjugated estrogen, estradiol, ethinyl estradiol)
  • eszopiclone
  • everolimus
  • fesoterodine
  • flibanserin
  • galantamine
  • grapefruit juice
  • guanfacine
  • hepatitis C antivirals (e.g., elbasvir, grazoprevir, glecaprevir, pibrentasvir)
  • HIV protease inhibitors (e.g., atazanavir, indinavir, saquinavir)
  • HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., efavirenz, etravirine, nevirapine, rilpivirine)
  • ivabradine
  • lemborexant
  • letermovir
  • lumacaftor-ivacaftor
  • macitentan
  • macrolide antibiotics (e.g., clarithromycin, erythromycin)
  • maraviroc
  • mebendazole
  • mefloquine
  • methadone
  • metoprolol
  • mifepristone
  • mirtazapine
  • modafinil
  • naloxegol
  • narcotic pain medications (e.g., codeine, fentanyl, meperidine, morphine, oxycodone, tramadol)
  • orlistat
  • oxybutynin
  • phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
  • protein kinase inhibitors (e.g., acalabrutinib, bosutinib, dasatinib, ibrutinib, lapatinib, nilotinib)
  • quinine
  • rifabutin
  • rifampin
  • riociguat
  • rivaroxaban
  • roflumilast
  • romidepsin
  • St. John's wort
  • saxagliptin
  • seizure medications (e.g., carbamazepine, lamotrigine, phenobarbital, phenytoin, primidone, valproic acid)
  • selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, paroxetine, sertraline)
  • sirolimus
  • solifenacin
  • "statin" anti-cholesterol medications (e.g., atorvastatin, lovastatin, simvastatin)
  • tacrolimus
  • theophylline
  • thyroid medications (e.g., levothyroxine, liothyronine, thyroid [dessicated])
  • ticagrelor
  • tolterodine
  • tolvaptan
  • trazodone
  • "triptan" migraine medications (e.g., almotriptan, eletriptan, sumatriptan)
  • warfarin
  • zidovudine
  • zolpidem
  • zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

All material copyright MediResource Inc. 1996 – 2022. Terms and conditions of use. The contents herein are for informational purposes only. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Source: www.medbroadcast.com/drug/getdrug/Paxlovid