Formulary
Nirmatrelvir with ritonavir: Indications, Dosing, Side Effects and Interactions
For nirmatrelvir with ritonavir Nirmatrelvir is a peptidomimetic inhibitor of coronavirus 3C-like protease which prevents multiplication of SARS-CoV-2.
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Nirmatrelvir with ritonavir: Indications, Dosing, Side Effects and Interactions
For nirmatrelvir with ritonavir Nirmatrelvir is a peptidomimetic inhibitor of coronavirus 3C-like protease which prevents multiplication of SARS-CoV-2.
Drug action
For nirmatrelvir with ritonavir Nirmatrelvir is a peptidomimetic inhibitor of coronavirus 3C-like protease which prevents multiplication of SARS-CoV-2. Ritonavir inhibits CYP3A-mediated metabolism of nirmatrelvir thereby increasing the plasma concentration of nirmatrelvir.
Indications and dose
**COVID-19 in patients who do not require oxygen supplementation and are at an increased risk of severe COVID-19 infection**
- **Adult** (By Mouth): 300 mg (two pink tablets) and 100 mg (one white tablet) twice daily for 5 days, to be initiated as soon as possible after SARS-CoV-2 positive result and within 5 days of symptom onset, for each dose, nirmatrelvir (pink tablets) and ritonavir (white tablet) to be taken together.
Cautions
For nirmatrelvir with ritonavir Hepatitis; liver enzyme abnormalities; pre-existing liver diseases; uncontrolled or undiagnosed HIV-1 infection Cautions, further information HIV-1 infection As nirmatrelvir is co-administered with ritonavir, there may be a risk of developing resistance to HIV protease inhibitors in patients with uncontrolled or undiagnosed HIV-1 infection. M
Side effects
For nirmatrelvir with ritonavir Common or very common Diarrhoea; taste altered; vomiting
Pregnancy
Important safety information For nirmatrelvir with ritonavir MHRA/CHM advice: COVID-19 antivirals: reporting to the UK COVID-19 Antivirals Pregnancy Registry (February 2022) The safety of COVID-19 antiviral treatment, such as nirmatrelvir with ritonavir, during pregnancy has not been established. The MHRA, in collaboration with the UK Teratology Information Service (UKTIS), is operating the UK COVID-19 Antivirals Pregnancy Registry to collect information about and enable follow-up of reported exposures to COVID-19 antivirals in pregnancy; it is also collecting information on the outcomes of pregnancies, where conception occurred during or shortly after paternal exposure to antiviral treatment. Healthcare professionals in England, Scotland, and Wales (as well as patients and their partners) are advised to report exposure to nirmatrelvir with ritonavir during pregnancy or around the time of conception, or of partners on nirmatrelvir with ritonavir around the time of conception. Healthcare professionals in Northern Ireland cannot currently report on behalf of a pregnant female or their partner but should encourage them to self-report. Since exposure can occur in very early pregnancy before pregnancy is recognised, healthcare professionals are advised to report (or to encourage patients to self-report), even if some time has passed since the end of nirmatrelvir with ritonavir treatment. An exposed pregnancy should be reported by telephone to UKTIS-for more information, see the UKTIS Registry website (available at: ). MHRA/CHM advice: Nirmatrelvir with ritonavir ( Paxlovid ): be alert to the risk of drug interactions with ritonavir (November 2023) There is a risk of harmful interactions with the ritonavir component of Paxlovid due to its potent inhibition of CYP3A4. Healthcare professionals are advised to obtain a detailed patient history of current medicines (including over-the-counter preparations, herbal remedies, and illicit or recreational drug use) and to consult resources, including product literature, for known and potential interactions before prescribing Paxlovid . Patients should be informed of this risk and advised not to change or stop taking any medicines without consulting a healthcare professional.
Breast feeding
For nirmatrelvir with ritonavir Avoid during treatment and for 7 days after last treatment. M
Hepatic impairment
For nirmatrelvir with ritonavir Avoid in severe impairment (no information available). M
Renal impairment
For nirmatrelvir with ritonavir Caution in moderate impairment; avoid in severe impairment (increased exposure). M Dose adjustments Reduce dose to 150 mg nirmatrelvir (one pink tablet) and 100 mg ritonavir (one white tablet) twice daily in moderate impairment. M
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Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
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