What is the appropriate dose of Paxlovid (nirmatrelvir/ritonavir) for a patient with complex medical history and normal renal function presenting with Covid-19?

Paxlovid Dosing for Patient with Normal Renal Function

This patient should receive the standard dose of Paxlovid: 300 mg nirmatrelvir (two 150 mg tablets) with 100 mg ritonavir (one 100 mg tablet) taken together twice daily for 5 days. 1

Renal Function Assessment

• The patient's GFR of 115 mL/min indicates normal renal function, requiring no dose adjustment 1, 2
• The creatinine of 0.62 mg/dL further confirms adequate kidney function for standard dosing 1
• Dose reduction is only necessary when eGFR falls below 60 mL/min (moderate renal impairment: 150 mg nirmatrelvir with 100 mg ritonavir twice daily) or below 30 mL/min (severe impairment: modified dosing schedule) 1, 2

Critical Drug Interaction Considerations

Before prescribing, you must review all current medications due to ritonavir's potent CYP3A4 inhibition, which can cause severe, life-threatening drug interactions 1, 3:

Medications Requiring Immediate Action:

• Hold statins (atorvastatin, simvastatin, lovastatin) during the 5-day treatment course due to rhabdomyolysis risk; pravastatin is the preferred alternative if lipid management cannot be interrupted 3
• Reduce or hold benzodiazepines (alprazolam, triazolam, oral midazolam) due to excessive sedation risk 3
• Adjust anticoagulants if the patient is on apixaban or dabigatran, with close monitoring 3
• Reduce opioid doses by 50-75% if taking fentanyl, oxycodone, or hydrocodone due to respiratory depression risk 3

Specific to This Patient's Conditions:

• Hypothyroidism medications (levothyroxine) typically do not interact significantly and can be continued 1
• Bipolar medications require careful review: avoid carbamazepine (potent CYP3A4 inducer), use caution with lamotrigine, and lithium generally has no interaction 3, 1
• Antihypertensives: Most are safe, but calcium channel blockers may require blood pressure monitoring due to increased drug levels 3

Treatment Timing and Administration

• Initiate treatment immediately since the patient has a positive COVID-19 test; Paxlovid must be started within 5 days of symptom onset for maximum efficacy 1, 4
• Administer with or without food at approximately the same time each day 1
• All three tablets (two nirmatrelvir + one ritonavir) must be taken together twice daily 1
• Treatment duration is exactly 5 days; do not extend or shorten 1

Expected Efficacy in This Patient Population

• Paxlovid reduces hospitalization or death by 89% in high-risk unvaccinated patients with mild COVID-19 4, 5
• The patient's multiple comorbidities (morbid obesity, hypertension, hypothyroidism) place her at high risk for severe COVID-19 progression, making treatment strongly indicated 4, 6
• Real-world effectiveness shows 39% reduction in hospitalization risk and 61% reduction in death across diverse populations, including vaccinated patients 6
• Absolute risk reduction is particularly pronounced in patients with multiple risk factors 6

Safety Profile and Monitoring

• Most common adverse effects are dysgeusia (altered taste, 5.6%) and diarrhea (3.1%), which are generally mild 1, 4
• Serious adverse events are rare (1.6% vs 6.6% with placebo) 4
• Monitor for hypersensitivity reactions including anaphylaxis, though rare 1
• Drug interactions persist for 2-3 days after the last dose due to ritonavir's prolonged CYP3A4 inhibition 3

Critical Contraindications to Verify

Do not prescribe Paxlovid if the patient is taking 1:

• Potent CYP3A inducers (rifampin, carbamazepine, phenytoin, St. John's wort)
• Drugs highly dependent on CYP3A4 with narrow therapeutic indices (ergot derivatives, pimozide, lurasidone, certain antiarrhythmics like amiodarone)
• History of clinically significant hypersensitivity to nirmatrelvir or ritonavir 1

Practical Implementation

Use the Liverpool COVID-19 Drug Interaction Checker (available online) to systematically review the patient's complete medication list before prescribing 3. This tool identifies all potential CYP3A4 and P-glycoprotein substrate interactions that require management 3.