VIRAC REX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for VIRAC REX (VIRAC REX).
VirAcRex is a direct-acting antiviral that inhibits the viral RNA-dependent RNA polymerase (NS5B) by acting as a chain terminator, thereby blocking viral replication.
| Metabolism | Primarily metabolized by CYP3A4 and to a lesser extent by CYP2C8. Also undergoes glucuronidation via UGT1A1. Elimination is mainly biliary (~90%) with renal excretion as minor route (~10%). |
| Excretion | Renal: 30-40% unchanged; biliary/fecal: 50-60% as metabolites; <10% in feces as parent drug. |
| Half-life | Terminal elimination half-life: 2.5-3.5 hours; clinical context: requires thrice-daily dosing to maintain therapeutic levels. |
| Protein binding | 85% bound to albumin; minor binding to α1-acid glycoprotein. |
| Volume of Distribution | 0.5-0.7 L/kg; indicates moderate tissue distribution; does not cross blood-brain barrier significantly. |
| Bioavailability | Oral: 65-75%; topical: 5-10% systemically absorbed; intramuscular: 90%. |
| Onset of Action | Oral: 30-60 min; IV: immediate (5-10 min); topical: 2-4 hours for local effect. |
| Duration of Action | Oral: 4-6 hours; IV: 3-5 hours; topical: 6-8 hours; clinical notes: duration correlates with plasma concentration above MIC. |
300 mg orally once daily with or without food.
| Dosage form | SOLUTION |
| Renal impairment | For CrCl 30-50 mL/min: 200 mg once daily; CrCl 15-29 mL/min: 100 mg once daily; CrCl <15 mL/min or hemodialysis: 100 mg every other day. |
| Liver impairment | Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose to 200 mg once daily; Child-Pugh Class C: not recommended (insufficient data). |
| Pediatric use | Not approved for patients under 18 years. No weight-based guidelines established. |
| Geriatric use | Start at lower end of dosing range (200 mg once daily) due to age-related renal decline; monitor renal function regularly. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for VIRAC REX (VIRAC REX).
| Breastfeeding | No human data; M/P ratio unknown. Excreted in rat milk. Breastfeeding not recommended due to potential for adverse effects in infant. |
| Teratogenic Risk | No human data; animal studies show teratogenic effects at doses 0.5 times human AUC. First trimester risk unknown; avoid in pregnancy unless benefit outweighs risk. Second and third trimesters: limited data, but potential for fetal growth restriction. |
| Fetal Monitoring |
■ FDA Black Box Warning
Risk of hepatitis B virus (HBV) reactivation in patients co-infected with HCV and HBV. Test all patients for evidence of current or prior HBV infection before initiating treatment. Monitor for HBV reactivation during and after treatment.
| Serious Effects |
Absolute: Hypersensitivity to VirAcRex or any component; severe hepatic impairment (Child-Pugh C); co-administration with strong CYP3A4 inducers (e.g., rifampin, carbamazepine). Relative: Caution in moderate hepatic impairment; caution with moderate CYP3A4 inducers.
| Precautions | Hepatitis B reactivation; hepatic decompensation in patients with cirrhosis; risk of reduced efficacy with proton pump inhibitors; potential drug interactions with strong CYP3A4 inducers; pregnancy and contraception requirements. |
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| Monitor liver function tests (LFTs) monthly; complete blood count (CBC) every 4 weeks; fetal ultrasound for growth assessment every 4-6 weeks during second and third trimesters. |
| Fertility Effects | Reversible impairment of spermatogenesis in animal studies; human data limited. May reduce female fertility via hormonal disruption. |