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Ritonavir

Antiretroviralprescriptionoral · inferred

HIV protease inhibitor used almost exclusively at low dose (100 mg) as a pharmacokinetic booster. It inhibits CYP3A4 (mechanism-based), raising plasma levels of co-administered drugs (other PIs, nirmatrelvir, etc). Also a potent P-gp inhibitor acutely and a PXR inducer chronically. Full-dose anti-HIV use is rare due to GI and metabolic toxicity.

Projected serum levels — 100 mg, twice daily

Ritonavir
Ritonavir modeled serum levels, 100 mg twice daily over 15 days Population-based pharmacokinetic estimate. Steady state reached after approximately 1 days. 0 12.5 25 37.5 50 Day 0 Day 4 Day 7 Day 11 Day 15 Time on a regular schedule ≈ steady state · day 1
Ritonavir modeled serum levels with a loading dose of 136 mg, then 100 mg twice daily The first dose is larger so levels approach steady state faster. 0 12.5 25 37.5 50 Day 0 Day 4 Day 7 Day 11 Day 15 Time on a regular schedule

Maintenance schedule: 100 mg twice daily (oral).

Loading schedule: 136 mg on day 1, then 100 mg twice daily — reaching therapeutic levels sooner.

Modeled steady state after ~1 days: peak ≈ 48.0 mg, trough ≈ 20.1 mg body load. Population-based estimate over 15 days for a 100 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.

Key facts

Category
Antiretroviral
Route modeled
Oral
Model confidence
inferred
Half-life
5 h
Common dose
100 mg
Suggested maximum
600 mg/day
Reference dose range
50–600 mg (single dose)
Suggested cadence
twice daily
Validated against
100 mg oral — Cmax 1.2 mg/L at 4 h

Documented interactions

  • contraindicated
    Alfuzosin (Uroxatral) + Ritonavir CYP inhibition

    Ritonavir mechanism_based of CYP3A4 predicted to change Alfuzosin (Uroxatral) AUC by ~10.00x

  • contraindicated
    Alprazolam (Xanax) + Ritonavir CYP inhibition

    Ritonavir mechanism_based of CYP3A4 predicted to change Alprazolam (Xanax) AUC by ~10.00x

  • contraindicated
    Amlodipine (Norvasc) + Ritonavir CYP inhibition

    Ritonavir mechanism_based of CYP3A4 predicted to change Amlodipine (Norvasc) AUC by ~10.00x

  • contraindicated
    Anastrozole (Arimidex) + Ritonavir CYP inhibition

    Ritonavir mechanism_based of CYP3A4 predicted to change Anastrozole (Arimidex) AUC by ~5.14x

  • contraindicated
    Astaxanthin + Ritonavir CYP inhibition

    Ritonavir mechanism_based of CYP3A4 predicted to change Astaxanthin AUC by ~10.00x

  • contraindicated
    Atogepant (Qulipta) + Ritonavir CYP inhibition

    Ritonavir mechanism_based of CYP3A4 predicted to change Atogepant (Qulipta) AUC by ~10.00x

Serum checks 515 modeled interaction pairings for ritonavir across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.

Research behind this entry

  1. Pharmacokinetics of ritonavir Zeldin RK, Petruschke RA · Clinical Pharmacokinetics, 2004 DOI

    Reviews ritonavir PK, highlighting nonlinear clearance, CYP3A4/P-gp inhibition, and the basis for booster dosing.

  2. Low-dose ritonavir moderately enhances nelfinavir exposure Kurowski M et al. · Clinical Pharmacology & Therapeutics, 2002 DOI

    Quantifies the boosting effect of 100 mg ritonavir on a CYP3A4-substrate protease inhibitor.

2 published studies referenced in the app, each with a plain-language summary.