NORVIR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for NORVIR (NORVIR).
Protease inhibitor; inhibits HIV-1 protease, preventing cleavage of viral polyprotein precursors into functional proteins, resulting in immature noninfectious viral particles.
| Metabolism | Primarily hepatic via CYP3A4 (major) and CYP2D6 (minor); also inhibits CYP3A4. |
| Excretion | Renal: 3.5% as unchanged drug; fecal: 86.4% (primarily metabolites); hepatic metabolism accounts for >95% of clearance. |
| Half-life | 3–5 hours (terminal half-life in adults); not significantly prolonged in renal impairment; may be slightly prolonged in hepatic impairment. |
| Protein binding | 98–99% bound to plasma proteins (mainly alpha-1-acid glycoprotein and albumin). |
| Volume of Distribution | 0.5 L/kg (steady state); indicates extensive tissue distribution beyond plasma volume. |
| Bioavailability | Oral: ~60–80% (with food); absolute bioavailability not fully established; increased with high-fat meal. |
| Onset of Action | Oral solution: peak plasma concentration at ~2–4 hours; capsule: ~4 hours; clinical antiviral effect begins within 24–48 hours of initiation. |
| Duration of Action | Cmax declines rapidly with t1/2 of 3–5 hours; trough levels maintained with q12h dosing; full antiviral suppression requires adherence. |
NORVIR (ritonavir) is primarily used as a pharmacokinetic booster. For boosting: 100 mg once or twice daily orally with food. As an antiviral: 600 mg twice daily orally with food.
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for renal impairment, including hemodialysis. |
| Liver impairment | Mild to moderate hepatic impairment (Child-Pugh A or B): reduce dose by 25% (e.g., 100 mg once daily). Child-Pugh C: contraindicated or avoid use. |
| Pediatric use | For boosting: weight-based dosing: 15-20 kg: 50 mg once or twice daily; 20-30 kg: 80 mg once or twice daily; 30-40 kg: 100 mg once or twice daily; >40 kg: 100 mg twice daily. Use oral solution for accurate dosing. Check product labeling for specific guidelines. |
| Geriatric use | No specific dose adjustment; use with caution due to age-related decline in hepatic and renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for NORVIR (NORVIR).
| Breastfeeding | Ritonavir is excreted into human breast milk at low concentrations. The milk-to-plasma (M/P) ratio is approximately 0.1-0.3. Based on limited data, the estimated infant daily dose is less than 1% of the maternal therapeutic dose, which is considered clinically insignificant. However, breastfeeding is generally not recommended in HIV-infected mothers due to the risk of HIV transmission through breast milk. For other indications, caution is advised. |
| Teratogenic Risk | NORVIR (ritonavir) is classified as FDA Pregnancy Category B. Animal studies have shown no evidence of teratogenicity or fetal harm at systemic exposures comparable to human therapeutic doses. In humans, data from the Antiretroviral Pregnancy Registry do not indicate an increased risk of major birth defects with first trimester exposure compared to the general population. However, due to the limited number of exposed pregnancies, a definitive risk assessment cannot be made. No specific trimester-specific risks have been identified. |
■ FDA Black Box Warning
Contraindicated with drugs highly dependent on CYP3A for clearance that are associated with life-threatening adverse events (e.g., alfuzosin, amiodarone, ergot derivatives, lovastatin, simvastatin, oral midazolam, triazolam, etc.).
| Serious Effects |
Concomitant use with drugs that are highly dependent on CYP3A4 for clearance and for which elevated plasma concentrations are associated with serious and/or life-threatening events (e.g., alfuzosin, amiodarone, cisapride, ergot derivatives, lomitapide, lovastatin, simvastatin, oral midazolam, triazolam, sildenafil for pulmonary arterial hypertension). Also contraindicated with rifampin, St. John's wort, and in patients with severe hepatic impairment.
| Precautions | Hepatotoxicity, pancreatitis, PR interval prolongation, new-onset diabetes/hyperglycemia, hemolytic anemia, fat redistribution, immune reconstitution syndrome, hyperlipidemia, and risk of bleeding in hemophiliacs. |
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| Fetal Monitoring | Monitor maternal liver function tests (AST, ALT, bilirubin), renal function, and blood glucose levels periodically. Assess for signs of pancreatitis and lactic acidosis. Fetal monitoring includes standard prenatal ultrasound for growth and anatomy. No specific fetal monitoring beyond routine obstetric care is required. |
| Fertility Effects | In animal studies, ritonavir did not impair fertility in male or female rats at systemic exposures up to 1.3 times the human therapeutic exposure. Human data on fertility effects are lacking. There are no reported adverse effects on human fertility. |