Paxlovid Dosing
For adults with normal renal function (eGFR ≥60 mL/min), prescribe nirmatrelvir 300 mg (two 150 mg tablets) plus ritonavir 100 mg (one 100 mg tablet) taken together orally twice daily for 5 days; for moderate renal impairment (eGFR 30–59 mL/min), reduce the dose to nirmatrelvir 150 mg (one 150 mg tablet) plus ritonavir 100 mg (one 100 mg tablet) twice daily for 5 days. 1
Standard Dosing Regimen
- Normal renal function (eGFR ≥60 mL/min): Administer nirmatrelvir 300 mg with ritonavir 100 mg (total of 3 tablets) orally every 12 hours for 5 consecutive days. 1
- Initiate treatment as soon as possible after COVID-19 diagnosis and within 5 days of symptom onset, even if baseline symptoms are mild. 1
- The tablets can be taken with or without food and must be swallowed whole—do not crush, chew, or break them. 1
Dose Adjustment for Renal Impairment
- Mild renal impairment (eGFR 60–89 mL/min): No dose adjustment is required; use the standard 300 mg/100 mg twice-daily regimen. 1
- Moderate renal impairment (eGFR 30–59 mL/min): Reduce nirmatrelvir to 150 mg while maintaining ritonavir at 100 mg (total of 2 tablets), administered twice daily for 5 days. 2, 3, 1
- Severe renal impairment (eGFR <30 mL/min): Paxlovid is not recommended because the appropriate dosage has not been established and safety data are lacking. 1
Critical Administration Details
- Nirmatrelvir must be co-administered with ritonavir. Failure to give both components together results in insufficient nirmatrelvir plasma levels and loss of therapeutic effect. 1
- Prescriptions should specify the numeric dose of each active ingredient (nirmatrelvir and ritonavir) to avoid dispensing errors. 1
- If a dose is missed within 8 hours of the scheduled time, take it immediately and resume the normal schedule; if more than 8 hours have elapsed, skip the missed dose and take the next dose at the regular time—never double the dose. 1
Monitoring During Treatment
- Reassess renal function if the patient's clinical status deteriorates, because COVID-19 itself can cause acute kidney injury, which would further increase nirmatrelvir levels and necessitate dose adjustment. 3
- Monitor for common adverse effects—dysgeusia (altered taste) and diarrhea—which occur more frequently than with placebo but rarely require discontinuation. 3, 1
- Watch for signs of drug accumulation (e.g., worsening dysgeusia or diarrhea) in patients with borderline or fluctuating renal function. 3
Drug Interaction Screening
- Before prescribing Paxlovid, systematically check all concomitant medications using the Liverpool COVID-19 Drug Interaction Tool, because ritonavir is a potent CYP3A4 inhibitor that can cause life-threatening interactions. 3, 4, 1
- Ritonavir-mediated interactions persist during the 5-day treatment course and for several days after completion. 2, 3
- Certain medications (e.g., simvastatin, lovastatin, ranolazine) are contraindicated and must be temporarily discontinued; others require dose adjustment or additional monitoring. 3, 1
Hepatic Impairment Considerations
- Mild to moderate hepatic impairment (Child-Pugh Class A or B): No dose adjustment is needed. 1
- Severe hepatic impairment (Child-Pugh Class C): Paxlovid is not recommended because pharmacokinetic and safety data are unavailable. 3, 1
Common Pitfalls to Avoid
- Do not delay initiation due to concerns about drug interactions or anticoagulation management—the interactions are manageable with dose adjustments, and Paxlovid must be started within 5 days of symptom onset to be effective. 2, 3
- Do not prescribe Paxlovid for patients hospitalized primarily for non-COVID conditions who incidentally test positive; clinical judgment should guide whether treatment is appropriate in this setting. 3
- Do not use Paxlovid as pre-exposure or post-exposure prophylaxis—it is not approved for prevention of COVID-19. 1
- Do not forget to counsel patients about the renal dosing instructions and the importance of completing the full 5-day course. 1