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. |
| Molecular Weight | 319.4 |
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 | Insufficient human data; animal studies show risk. Use only if benefit outweighs potential teratogenic risk. |
| 2nd trimester | Limited human data; no evidence of fetal harm from reported cases, but caution advised. |
| 3rd trimester | Risk of neonatal hemorrhage if used near term; avoid unless essential. |
Clinical note
Comprehensive clinical and safety monograph for VIRAC REX (VIRAC REX).
| Placental transfer | Crosses placenta in humans; detectable in fetal serum at maternal levels (approx. 50-100%). |
| Breastfeeding | Excreted in breast milk in low amounts. Monitor infant for diarrhea and rash. Consider benefits of breastfeeding versus risk of infant exposure. |
| Lactation Rating |
■ 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 |
Hypersensitivity to VIRAC REX or any componentSevere hepatic impairment
| 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. |
| Food/Dietary | Take VIRAC REX with food to enhance TDF absorption. Avoid concurrent use with nephrotoxic agents (e.g., aminoglycosides, NSAIDs, amphotericin B, foscarnet, vancomycin, cidofovir) as they may increase risk of renal impairment. Do not coadminister with other tenofovir-containing products (e.g., Atripla, Complera, Stribild, Truvada) or other antiretrovirals containing emtricitabine or lamivudine. Chronic high-dose alcohol consumption may worsen hepatotoxicity risk. No specific dietary restrictions other than taking with food. |
Loading safety data…
| L3 (Moderately Safe) |
| 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 | 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. |
| Clinical Pearls | VIRAC REX is a fixed-dose combination of tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC), used for HIV-1 pre-exposure prophylaxis (PrEP) and in combination with other antiretrovirals for HIV-1 treatment. Monitor renal function (serum creatinine, estimated creatinine clearance, urine glucose, and urine protein) at baseline and periodically due to TDF nephrotoxicity. Test for hepatitis B virus (HBV) before initiating because FTC and TDF are active against HBV, and acute exacerbations can occur upon discontinuation in HBV-coinfected patients. HIV screening must be confirmed negative before starting PrEP and repeated every 3 months to detect seroconversion. Advise patients that VIRAC REX does not protect against other sexually transmitted infections and must be used with condoms. |
| Patient Advice | Take one tablet daily at roughly the same time each day to maintain consistent drug levels. If you miss a dose, take it as soon as you remember unless it is almost time for the next dose; do not double up. · Do not use VIRAC REX alone for HIV treatment; it must be combined with other antiretroviral agents. For PrEP, you must be HIV-negative before starting and test every 3 months while on treatment. · Report symptoms of lactic acidosis (unusual muscle pain, trouble breathing, stomach pain with nausea/vomiting, fast or irregular heartbeat, dizziness, feeling cold) or hepatotoxicity (yellowing of skin/eyes, dark urine, light-colored stools, loss of appetite, right upper belly pain) immediately. · Tell your healthcare provider if you have kidney disease, bone problems (including osteoporosis), or hepatitis B virus infection, as stopping VIRAC REX can cause a severe HBV flare-up. · Use effective contraception if capable of pregnancy; VIRAC REX may reduce the efficacy of hormonal contraceptives. Discuss alternative or additional barrier methods. · Do not breastfeed while taking VIRAC REX to avoid transmitting HIV or antiretroviral drugs to the infant. |