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COVID-19 Antiviral — Protease Inhibitor Combination

Nirmatrelvir / Ritonavir

Brand names: Paxlovid

Nirmatrelvir with ritonavir is an oral antiviral combination used to treat mild to moderate COVID-19 in adults at increased risk of progression to severe disease.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

Nirmatrelvir inhibits the SARS-CoV-2 main protease (Mpro/3CL protease) to block viral replication, and low-dose ritonavir inhibits CYP3A4 to maintain adequate nirmatrelvir levels.

Prescribing in practice

  • The ritonavir component causes numerous serious CYP3A-mediated drug interactions, so a full medication review for contraindicated and interacting drugs is essential before prescribing.
  • It must be started as early as possible and within the recommended window from symptom onset, and dose adjustment is needed in moderate renal impairment with avoidance in severe impairment.
  • It is contraindicated in severe hepatic impairment and with drugs highly dependent on CYP3A for clearance where raised levels could be dangerous.

Monitoring

No routine laboratory monitoring is needed, but renal function should be checked and the medication list screened for interactions before and during treatment.

Counselling the patient

  • Tell your clinician and pharmacist about every medicine, supplement and recreational drug you take before starting.
  • Begin the course as soon as possible after diagnosis and complete it even if you feel better.

Evidence & guidelines

Use is supported by the EPIC-HR trial and guided in the UK by MHRA authorisation and NICE recommendations.

Reference: Hammond et al. NEJM 2022 (EPIC-HR); NICE TA878; MHRA SPC Paxlovid; Liverpool COVID-19 Drug Interactions; UKHSA COVID therapeutics guidance; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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