Nirmatrelvir 150 mg & Ritonavir 100 mg (Paxlovid) – COVID-19 Treatment, Dosage, Side Effects

1. Composition:

• Nirmatrelvir 150 mg Ritonavir 100 mg about Nirmatrelvir 150 mg: A SARS-CoV-2 main protease (Mpro, also known as 3CLpro) inhibitor.
• Ritonavir 100 mg: Originally developed for HIV, used here as a pharmacokinetic booster (it inhibits the enzyme that metabolizes nirmatrelvir, increasing its levels in the blood).

2. Indications:

• Treatment of mild-to-moderate COVID-19 in adults and pediatric patients (12 years and older, weighing at least 40 kg) who are at high risk for progression to severe COVID-19, including hospitalization or death.
• Must be started within 5 days of symptom onset.

3. Mechanism of Action:

• Nirmatrelvir:

• Inhibits the main protease (Mpro) of SARS-CoV-2, an enzyme essential for viral replication.
• By blocking this enzyme, it prevents the virus from processing polyproteins needed for its replication.

• Ritonavir:

• It does not act directly on SARS-CoV-2 but inhibits CYP3A4, an enzyme that metabolizes many drugs including nirmatrelvir.
• This inhibition boosts the concentration and effectiveness of nirmatrelvir.

4. Dosage:

• 300 mg of Nirmatrelvir (two 150 mg tablets) + 100 mg of Ritonavir (one tablet) taken together twice daily for 5 days.
• Total of 6 tablets per day (3 in the morning, 3 in the evening).

Note: Dose adjustments may be needed in patients with moderate renal impairment. Not recommended in severe renal or hepatic impairment.

5. Common Side Effects:

• Altered taste (dysgeusia)
• Diarrhea
• High blood pressure
• Muscle aches
• Liver enzyme elevations
• Allergic reactions (rare)

6. Contraindications:

• Severe liver or kidney disease
• Concomitant use with drugs that are highly dependent on CYP3A for clearance and for which elevated concentrations are associated with serious reactions (e.g., certain antiarrhythmics, sedatives, ergot alkaloids).
• Ritonavir has many drug interactions, including with:
  • Antiarrhythmics
  • Anticonvulsants
  • Statins (simvastatin, lovastatin)
  • Some antipsychotics
  • St. John’s Wort

7. Use in Special Populations:

• Pregnancy: Limited data; use only if potential benefit outweighs risk.
• Breastfeeding: Unknown if nirmatrelvir is excreted in human milk.
• Children under 12: Not authorized.
• Elderly: No dose adjustment solely based on age, but monitor for renal function.

8. Storage:

• Store below 25°C (77°F) in the original packaging to protect from moisture.