VALNAC
Clinical safety rating: caution
Comprehensive clinical and safety monograph for VALNAC (VALNAC).
Valproate semisodium (valproic acid derivative) increases GABA levels in the brain by inhibiting GABA transaminase and succinic semialdehyde dehydrogenase, and modulates voltage-gated sodium channels and T-type calcium channels. The combination (valproate semisodium) dissociates in the gastrointestinal tract to valproic acid and sodium valproate, providing rapid absorption and sustained release.
| Metabolism | Hepatic metabolism via glucuronidation (UGT1A3, UGT2B7, UGT2B15) and beta-oxidation; minor CYP2C9 involvement. Valproate is a substrate of CYP2C9 and inhibitor of CYP2C9, epoxide hydrolase, and UGTs. |
| Excretion | Primarily renal (90% unchanged drug), with 10% biliary-fecal. In renal impairment, half-life prolongs significantly, requiring dose adjustment. |
| Half-life | 3-5 hours (healthy adults). In severe renal impairment (CrCl <30 mL/min), half-life extends to 12-24 hours, increasing risk of accumulation and toxicity. |
| Protein binding | 90%, primarily to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | 0.5 L/kg (suggesting moderate tissue penetration with distribution into total body water). |
| Bioavailability | Oral: 75% (due to first-pass metabolism). IM: 90%. IV: 100%. Topical: 10-20% (systemic absorption highly variable). |
| Onset of Action | Oral: 30-60 minutes; intravenous: immediately; intramuscular: 15-30 minutes; topical: variable (within 1 hour depending on formulation). |
| Duration of Action | 4-6 hours for oral/IV/IM; topical durations depend on formulation but generally 6-8 hours. Extended-release formulations may last 12-24 hours. Clinical effect correlates with plasma levels above a threshold of 1.5 mcg/mL. |
Adults: 650 mg orally twice daily, with a maximum of 1300 mg per day.
| Dosage form | CREAM |
| Renal impairment | GFR 30-60 mL/min: no adjustment needed; GFR 15-29 mL/min: reduce dose to 325 mg twice daily; GFR <15 mL/min: not recommended. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use. |
| Pediatric use | Weight-based: 10-15 mg/kg/dose twice daily; maximum 30 mg/kg/day. |
| Geriatric use | Start at 325 mg once daily; titrate slowly; monitor renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for VALNAC (VALNAC).
| Breastfeeding | Excreted in breast milk (M/P ratio 0.8). Limited evidence suggests risk of infant hepatic toxicity. Use caution; consider alternative therapy. |
| Teratogenic Risk | First trimester: Increased risk of neural tube defects and cardiac anomalies (OR 2.5-3.0). Second trimester: Risk of late abortion and preterm labor. Third trimester: Risk of neonatal hemorrhage and maternal hepatotoxicity. |
| Fetal Monitoring |
■ FDA Black Box Warning
Hepatotoxicity: fatal hepatic failure, especially in children <2 years old with mitochondrial disorders, polytherapy, or developmental delay. Pancreatitis: life-threatening, can occur anytime. Teratogenicity: neural tube defects, major congenital malformations, decreased IQ in offspring. Avoid in women of childbearing potential unless alternative treatments fail.
| Serious Effects |
Hypersensitivity to valproate or components, hepatic disease or significant dysfunction, known mitochondrial disorder (e.g., POLG mutations), urea cycle disorders (risk of hyperammonemic encephalopathy), pregnancy (especially for migraine prophylaxis; weight risk-benefit for bipolar/seizures), women of childbearing potential not using effective contraception (for migraine prophylaxis).
| Precautions | Hepatotoxicity risk: monitor LFTs, baseline liver disease, children <2 years, polytherapy. Pancreatitis: symptoms include abdominal pain, nausea/vomiting. Teratogenicity: pregnancy test, consider folic acid; not for bipolar during pregnancy. Hyperammonemic encephalopathy: check ammonia if altered mental status. Suicidal ideation: monitor for depression. Drug interactions: lamotrigine (increases rash risk), carbamazepine (decreases valproate, increases carbamazepine), aspirin (increases valproate concentrations). Monitoring: CBC, platelets, LFTs, ammonia levels, trough valproate levels (50-125 mcg/mL). |
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| Serum transaminases, bilirubin, and INR monthly; fetal ultrasound for anomalies at 18-20 weeks; nonstress test weekly after 32 weeks. |
| Fertility Effects | May impair spermatogenesis and oogenesis (reversible). No effect on ovulation or implantation in animal studies. |