Divalproex Sodium

Indications

• FDA-approved for acute manic and mixed episodes of bipolar I disorder in adults, with the extended-release form dosed once daily.
• FDA-approved for migraine prophylaxis in adults, though it is contraindicated in pregnancy for this indication because risk exceeds benefit.
• FDA-approved for complex partial seizures as monotherapy or adjunct from age 10, and for simple and complex absence seizures.
• Off-label maintenance treatment of bipolar I disorder, widely used and guideline-endorsed despite the absence of a maintenance indication.
• Off-label use for impulsive aggression and for alcohol withdrawal, though evidence in dementia-related agitation shows harm without benefit.
• Often preferred over lithium for mixed episodes, rapid cycling, and mania with comorbid substance use or head injury.

Mechanism of action

• Increases brain GABA availability by inhibiting GABA transaminase and succinic semialdehyde dehydrogenase, raising inhibitory tone.
• Blocks voltage-gated sodium channels and attenuates T-type calcium currents, which dampens high-frequency repetitive neuronal firing.
• Inhibits histone deacetylase and modulates extracellular signal-regulated kinase pathways, effects proposed to underlie mood stabilization.
• Reduces glutamatergic excitability and stabilizes kindling phenomena, consistent with its efficacy in mixed and rapid-cycling presentations.
• The antimanic effect appears within 3 to 5 days at therapeutic levels, faster than lithium and comparable to antipsychotic monotherapy.

Pharmacokinetics

• Divalproex dissociates to valproate in the gut; delayed-release peaks at 3 to 8 hours and the extended-release form at 4 to 17 hours.
• Protein binding is about 90 percent but saturable, so free valproate rises disproportionately at total levels above 100 mcg/mL.
• Elimination half-life is 9 to 16 hours in adults, shorter in patients taking enzyme-inducing anticonvulsants such as carbamazepine.
• Metabolism is mainly glucuronidation and mitochondrial beta-oxidation, with minor CYP2C9, CYP2C19, and CYP2A6 contributions.
• Valproate inhibits CYP2C9, UGT enzymes, and epoxide hydrolase, which drives its most important drug interactions.

Dosing

• For acute mania start delayed-release 750 mg/day in divided doses, or extended-release 25 mg/kg/day once daily, then titrate rapidly.
• Increase every 1 to 3 days to clinical response and a trough level of 50-125 mcg/mL; the labeled maximum is 60 mg/kg/day.
• Migraine prophylaxis starts at 250 mg twice daily or extended-release 500 mg daily, with a usual ceiling of 1000 mg/day.
• Extended-release tablets deliver about 10 to 20 percent less valproate than delayed-release, so raise the total dose when converting.
• Reduce the dose in hepatic impairment and avoid valproate entirely in significant liver disease; no adjustment is needed for renal impairment.
• Taper over weeks when stopping in seizure disorders; abrupt withdrawal can precipitate status epilepticus or mood destabilization.

Adverse effects

• Nausea, dyspepsia, and diarrhea are common early and are reduced by the delayed-release or extended-release formulations taken with food.
• Weight gain affects up to half of patients, and dose-related tremor, sedation, and cognitive slowing are frequent reasons for discontinuation.
• Hair thinning occurs in roughly 10 percent and often responds to a zinc and selenium supplement while the dose is maintained.
• Thrombocytopenia is dose-dependent and common above 100 mcg/mL; asymptomatic hyperammonemia may progress to encephalopathy.
• Polycystic ovary features, hyperandrogenism, and menstrual irregularity develop in a substantial minority of young women on valproate.
• Fatal hepatotoxicity and hemorrhagic pancreatitis are rare but can occur at any time and demand immediate discontinuation.

Monitoring

• Obtain liver enzymes and CBC with platelets at baseline, then every 1 to 2 months for the first 6 months and periodically thereafter.
• Check a trough valproate level 3 to 5 days after each dose change, aiming for 50 to 125 mcg/mL in mania and 50 to 100 mcg/mL in epilepsy.
• Measure serum ammonia when lethargy, confusion, vomiting, or unexplained encephalopathy appears, even with normal liver enzymes.
• Confirm a negative pregnancy test before starting in anyone who can become pregnant, and document effective contraception in the chart.
• Track weight, menstrual regularity, and signs of hyperandrogenism at each visit, plus amylase and lipase if abdominal pain develops.

Interactions

• Valproate roughly doubles lamotrigine concentrations by inhibiting glucuronidation, so lamotrigine starting and target doses must be halved.
• Carbapenem antibiotics can drop valproate levels by more than 50 percent within days, causing breakthrough seizures or mania.
• Enzyme inducers including carbamazepine, phenytoin, phenobarbital, and rifampin substantially lower valproate concentrations.
• Valproate raises free phenytoin and inhibits CYP2C9, increasing warfarin effect; aspirin displaces it from protein and raises free drug.
• Contraindicated in hepatic disease, urea cycle disorders, known mitochondrial POLG mutations, and pregnancy for migraine prophylaxis.

Special populations

• Valproate should not be used in anyone who can become pregnant unless other treatments are unacceptable, given a 1 to 2 percent neural tube defect rate.
• In utero exposure lowers childhood IQ by about 8 to 10 points relative to lamotrigine, an effect that persists at school age.
• Milk concentrations are low and breastfeeding is generally considered compatible, with infant platelet and liver monitoring if prolonged.
• Children under 2 years have the highest risk of fatal hepatotoxicity, especially on polytherapy or with metabolic disease.
• Older adults show reduced clearance and higher free fraction; start at lower doses and watch closely for sedation and dehydration.

Clinical pearls

• Add valproate to lamotrigine and you must halve the lamotrigine dose or risk Stevens-Johnson syndrome.
• Unexplained lethargy on a normal valproate level is hyperammonemia until an ammonia level says otherwise.
• Document contraception and pregnancy counseling at every visit for patients who can become pregnant.