Paxlovid Dosing for a 13-Year-Old
For a 13-year-old weighing ≥40 kg, administer nirmatrelvir/ritonavir 300 mg/100 mg twice daily for 5 days; if the patient weighs <40 kg, the dose should be reduced to 150 mg/100 mg twice daily.
Weight-Based Dosing Algorithm
The dosing of Paxlovid in adolescents follows a straightforward weight-based approach:
- Patients ≥40 kg: Standard adult dose of nirmatrelvir/ritonavir 300 mg/100 mg twice daily for 5 days 1
- Patients <40 kg: Reduced dose of nirmatrelvir/ritonavir 150 mg/100 mg twice daily for 5 days 1
Population pharmacokinetic modeling supports these dosing recommendations for pediatric patients aged 12 to <18 years, demonstrating that adolescents weighing ≥40 kg achieve similar systemic exposures to adults with the standard 300/100 mg twice daily regimen 1. The twice-daily dosing maintains nirmatrelvir trough concentrations at approximately 5.4 times the antiviral EC90 value, ensuring adequate viral suppression throughout the treatment course 2.
Renal Function Considerations
Critical caveat: Before prescribing, assess renal function in all adolescent patients:
- Normal renal function or mild impairment (eGFR ≥60 mL/min/1.73 m²): Use standard weight-based dosing as above 1, 3
- Moderate renal impairment (eGFR 30-59 mL/min/1.73 m²): Reduce to nirmatrelvir/ritonavir 150 mg/100 mg twice daily regardless of weight 1, 3
- Severe renal impairment (eGFR <30 mL/min/1.73 m²): Paxlovid is not recommended 3
Nirmatrelvir undergoes primarily renal elimination when co-administered with ritonavir, with systemic exposure increasing 187% in moderate renal impairment and 304% in severe renal impairment compared to normal function 3. The dose reduction in moderate impairment prevents excessive drug accumulation while maintaining therapeutic concentrations.
Administration Details
- Duration: Complete 5-day course regardless of symptom improvement 2
- Timing: Administer doses approximately 12 hours apart 2
- Food: Can be taken with or without food 2
Drug Interaction Screening
This is the most critical pitfall to avoid: Ritonavir is a potent CYP3A4 inhibitor that causes major drug-drug interactions 2, 4. Before prescribing to any adolescent:
- Review all concomitant medications for CYP3A4 substrates with narrow therapeutic indices
- Immunosuppressants require dramatic dose reductions or temporary discontinuation 5
- Anticoagulants may require dose adjustments and enhanced monitoring 4
- Many commonly used medications in adolescents (e.g., certain psychiatric medications, hormonal contraceptives) may be affected
The ritonavir component inhibits CYP3A4, CYP2D6, and P-glycoprotein, creating complex interaction profiles that persist for several days after treatment completion due to the time required for enzyme activity recovery 4.