Paxlovid (Nirmatrelvir/Ritonavir)
Fixed-dose oral antiviral for acute SARS-CoV-2 infection in patients at high risk for progression to severe COVID-19. Each 'dose' consists of two 150 mg nirmatrelvir tablets plus one 100 mg ritonavir tablet, taken twice daily for 5 days. Nirmatrelvir is the active SARS-CoV-2 Mpro (3CL protease) inhibitor; ritonavir is a pharmacokinetic booster (potent CYP3A4 inhibitor) used to maintain therapeutic nirmatrelvir exposures. Nirmatrelvir plasma half-life ~7h (boosted). CRITICAL DRUG INTERACTIONS: ritonavir's CYP3A4 inhibition causes severe interactions with dozens of common medications (statins, amiodarone, calcineurin inhibitors, rivaroxaban/apixaban, fentanyl, many antipsychotics, sildenafil, ergots, colchicine, etc.). Review all concomitant medications BEFORE prescribing, contraindicated or requires dose hold/adjustment for many. Renal dose adjustment required for eGFR 30-60 mL/min; avoid if eGFR <30.
Projected serum levels — 1 dose (≈ 400 mg), twice daily
Maintenance schedule: 1 dose (≈ 400 mg) twice daily (oral).
Loading schedule: 1.3 dose on day 1, then 1 dose (≈ 400 mg) twice daily — reaching therapeutic levels sooner.
Modeled steady state after ~1 days: peak ≈ 183 mg, trough ≈ 50.9 mg body load. Population-based estimate over 15 days for a reference dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.
Key facts
- Category
- Antiviral
- Route modeled
- Oral
- Model confidence
- inferred
- Half-life
- 4.9 h
- Common dose
- 1 dose (≈ 400 mg)
- Suggested maximum
- 2 dose/day
- Reference dose range
- 0.50–2 dose (single dose)
- Suggested cadence
- twice daily
Documented interactions
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contraindicated
Alfuzosin (Uroxatral) + Paxlovid (Nirmatrelvir/Ritonavir)
Paxlovid (Nirmatrelvir/Ritonavir) mechanism_based of CYP3A4 predicted to change Alfuzosin (Uroxatral) AUC by ~10.00x
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contraindicated
Alprazolam (Xanax) + Paxlovid (Nirmatrelvir/Ritonavir)
Paxlovid (Nirmatrelvir/Ritonavir) mechanism_based of CYP3A4 predicted to change Alprazolam (Xanax) AUC by ~10.00x
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contraindicated
Amlodipine (Norvasc) + Paxlovid (Nirmatrelvir/Ritonavir)
Paxlovid (Nirmatrelvir/Ritonavir) mechanism_based of CYP3A4 predicted to change Amlodipine (Norvasc) AUC by ~10.00x
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contraindicated
Anastrozole (Arimidex) + Paxlovid (Nirmatrelvir/Ritonavir)
Paxlovid (Nirmatrelvir/Ritonavir) mechanism_based of CYP3A4 predicted to change Anastrozole (Arimidex) AUC by ~5.14x
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contraindicated
Astaxanthin + Paxlovid (Nirmatrelvir/Ritonavir)
Paxlovid (Nirmatrelvir/Ritonavir) mechanism_based of CYP3A4 predicted to change Astaxanthin AUC by ~10.00x
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contraindicated
Atogepant (Qulipta) + Paxlovid (Nirmatrelvir/Ritonavir)
Paxlovid (Nirmatrelvir/Ritonavir) mechanism_based of CYP3A4 predicted to change Atogepant (Qulipta) AUC by ~10.00x
Serum checks 207 modeled interaction pairings for paxlovid (nirmatrelvir/ritonavir) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.
Research behind this entry
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Oral nirmatrelvir for high-risk, nonhospitalized adults with Covid-19 (EPIC-HR)
Pivotal phase 2/3 trial demonstrating 89% relative risk reduction in COVID-19 hospitalization/death with nirmatrelvir/ritonavir vs placebo when started within 5 days of symptom onset in high-risk unvaccinated adults.
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Innovative randomized phase 1 study and dosing regimen selection to accelerate and inform pivotal COVID-19 trial of nirmatrelvir
Phase 1 PK study establishing nirmatrelvir 300 mg + ritonavir 100 mg q12h dosing; ritonavir-boosted nirmatrelvir achieves target trough exposures ~6x EC90 for SARS-CoV-2 Mpro inhibition.
2 published studies referenced in the app, each with a plain-language summary.