Valproate

Written by Megan Boucher

Last updated 30th March 2026 •
7 Revisions

Valproate is a widely used broad-spectrum anti-seizure medication with additional indications in psychiatry and neurology. Its clinical utility spans epilepsy, bipolar disorder, and migraine prophylaxis; however, its use is significantly limited by serious safety concerns, particularly teratogenicity and neurodevelopmental risks. Understanding its pharmacology, monitoring requirements, and regulatory restrictions is essential for safe prescribing.

Valproate is available in multiple formulations, most commonly as sodium valproate (the sodium salt) or valproic acid (the free acid form). Although these formulations are often used interchangeably, subtle pharmacokinetic and dosing differences exist.

Mechanism of Action

Valproate has several sites of action consistent with its broad clinical effectiveness. 

Calcium Channels

Drugs that are effective in the treatment of absence seizures, share a common mechanism of blocking T-type low-voltage-activated calcium channels. These channels are vital in determining the rhythmic discharge of thalamic neurons associated with absence seizures.

GABA

Valproate increases gamma-aminobutyric acid (GABA) levels in the brain, which is an inhibitory neurotransmitter which helps to block impulses between nerves.

Enhancement of GABA activity is thought to occur via multiple mechanisms including:

  • Inhibition of GABA transaminase (which inactivates GABA)
  • Increased GABA release via a presynaptic effect on GABA(B) receptors
  • Enhanced GABA synthesis by activating glutamic acid decarboxylase (GAD)

Sodium Channels

Like phenytoin but to a lesser extent, valproate inhibits voltage-dependent sodium channels.

Created in BioRender. Boucher, M. (2026) https://BioRender.com/lriorba

Fig 1: Mechanism of Action of Valproate via inhibition of calcium and sodium channels, and enhancement of GABA activity.

Pharmacokinetics

The effective therapeutic range for plasma valproic acid levels is 40-100mg/L. The table below describes the pharmacokinetics for valproate. 

Parameter Details
Absorption Well absorbed orally
Distribution 85–94% protein bound; hypoalbuminaemia may result in increased free (active) drug levels despite normal total levels
Metabolism Hepatic metabolism via CYP2A6, CYP2B6, CYP2C19, CYP2C9, CYP2E1 (minor pathways); also inhibits CYP enzymes and UGT glucuronidation
Excretion Renal excretion; dose reduction required in renal impairment

Half life: 12–15 hours

Contraindications

Valproate is contraindicated in pregnancy unless two specialists independently confirm that no other effective or tolerated treatment options are available. Similarly, in women of childbearing potential under 55 years of age, valproate must not be used unless this same condition is met.

Patients with urea cycle disorders should not receive valproate because of the risk of hyperammonaemia. Likewise, individuals with uncorrected systemic primary carnitine deficiency are at risk of worsening deficiency and subsequent hyperammonemic encephalopathy. 

It is also contraindicated in patients with active liver disease due to the increased risk of hepatotoxicity. Furthermore, valproate must also be avoided in patients with mitochondrial disorders, such as Alpers–Huttenlocher syndrome, due to the significantly increased risk of severe liver toxicity.

Cautions and Adverse Effects

Valproate is a category two anti-seizure medicine (ASM), meaning that the brand provided to the patient should only be changed with caution when the patient is being treated for epilepsy. 

According to Specialist Pharmacy Service (SPS) guidance:

  • No dose adjustment is required when switching between Convulex (valproic acid) and sodium valproate formulations.`
  • A 10% dose increase is recommended when switching from semi-sodium valproate (e.g. Depakote) to sodium valproate

Foetal malformations

Sodium valproate is generally well tolerated compared to other anti-convulsants with low toxicity and lack of sedative effect, however its use is restricted in males and females (of childbearing age) due to a high risk of feotal malformations. 

There is a 30-40% risk of neurodevelopmental disorders and 11% risk of birth defects in children born to mothers taking valproate during pregnancy. Valproate must not be used in women of childbearing age unless a pregnancy prevention programme is in place. 

Furthermore, emerging evidence suggests a possible increased risk of neurodevelopmental disorders in children born to men treated with valproate in the 3 months prior to conception. 

Incident rates are 4-5.6% compared to 2.3-3.2% for males treated with lamotrigine/levetiracetam. Current recommendation includes use of effective contraception during treatment and for 3 months afterwards, and to consider alternative treatments if planning a family. Furthermore there is a risk of male infertility and testicular toxicity has been demonstrated in animals. 

The Pregnancy Prevention Programme:

The Pregnancy Prevention Programme (PPP) for valproate is a strict risk-minimisation strategy designed to prevent fetal exposure due to the drug’s high risk of congenital malformations, neurodevelopmental disorders, and lower birth weight. Before prescribing, a specialist must assess each patient’s individual circumstances and confirm that the patient fully understands these risks and the need for preventative measures. Valproate should only be used in females of childbearing potential when no suitable alternative exists, and treatment must be initiated only after a negative pregnancy test.

A central requirement of the programme is the use of highly effective contraception throughout treatment. Patients must be counselled on suitable methods; ideally a user-independent option (e.g. implant or intrauterine device), or two complementary methods. Regular specialist review (at least annually) is mandatory to reassess whether valproate remains the most appropriate therapy, with completion of a Risk Acknowledgement Form to document patient understanding.

The PPP also places strong emphasis on pregnancy planning and early action. Women must seek specialist advice before attempting conception so that switching to safer alternatives can be considered in advance. If pregnancy occurs, urgent referral to a specialist is required to review treatment and provide counselling. These precautions also extend to girls approaching menarche, with early planning to transition away from valproate wherever possible.

Pharmacists play a key supporting role by supplying educational materials (such as the Patient Card and Guide), reinforcing counselling messages, and advising patients not to stop valproate abruptly but to seek immediate medical advice if pregnancy is planned or suspected. Overall, the PPP ensures that valproate use in females is tightly controlled, continuously reviewed, and supported by clear patient education to minimise preventable harm.

Hepatotoxicity

Rarely, hepatotoxicity can occur, including fatal hepatic failure. This is most likely within the first 6 months of therapy, and liver function monitoring is essential during this period.

Risk factors include:

  • Age <3 years
  • Concomitant salicylate use
  • Carnitine deficiency
  • Urea cycle disorders

Other adverse effects and cautions include the following:

  • MHRA Alert for all antiepileptics was issued in 2008 after a meta-analysis of placebo controlled trials showed a small increased risk of suicidal thoughts and behaviour. Patients should be advised to seek medical advice if signs emerge.
  • Nausea
  • Hair thinning and curling of hair
  • Pancreatitis (idiosyncratic and is not related to dose or duration of therapy)
  • Metabolic effects such as weight gain, obesity and insulin resistance. 
  • Sudden cutaneous adverse reactions (SCARs) such as Stevens-Johnson Syndrome (SJS), Epidermal Necrolysis (TEN) and Drug reaction with eosinophilia and systemic symptoms (DRESS) and angioedema

Summary of Monitoring

Baseline tests: BMI, clotting, FBC, LFT, platelet, pregnancy count

Ongoing (6 months then annually): BMI, FBC, LFT

Prior to surgery / following any bleeding or bruising: Clotting screen, FBC [end-clinical]

Interactions

Valproate is associated with numerous clinically significant drug interactions due to its effects on hepatic enzyme systems and protein binding. It acts primarily as an enzyme inhibitor (notably of CYP enzymes and UGT-mediated glucuronidation), which can increase plasma concentrations of co-administered drugs. Additionally, valproate is highly protein bound, meaning it can displace other drugs from albumin, increasing their free (active) fraction. 

Conversely, certain enzyme-inducing drugs can reduce valproate levels, while others (such as carbapenems) can cause a rapid and clinically significant reduction in its plasma concentration. Understanding these interactions is essential to prevent toxicity or loss of seizure control.

Interactions for valproate are described in the table below: 

Interaction Type Drugs Effect Comments
Valproate Enzyme inhibition (CYP & UGT) Lamotrigine ↑ Lamotrigine levels  Via inhibition of UGT
Phenobarbital, Primidone ↑ Levels Increased sedation/toxicity, via CYP inhibition 
Nimodipine ↑ Levels Monitor for hypotension
Protein binding displacement Phenytoin Initial decrease in total phenytoin exposure which after continued therapy can then lead to a return to baseline or an increase in phenytoin levels.
Pharmacodynamic potentiation Antipsychotics, antidepressants, benzodiazepines ↑ CNS effects Increased sedation, CNS depression
Bone marrow toxicity risk Clozapine ↑ Risk of neutropenia, myocarditis Avoid or closely monitor
Hepatotoxicity risk Salicylates ↑ Valproate levels Avoid combination, especially in children
Reduced valproate levels (major interaction) Carbapenems (e.g. meropenem) ↓ Valproate (up to 60–100%) Avoid combination; add alternative anticonvulsant
Induction of CYP/UGT enzymes  (↓ valproate levels) Carbamazepine, phenytoin, rifampicin, phenobarbital, primidone, oestrogens ↓ Valproate levels Loss of seizure control → may need dose adjustment
Inhibition of CYP/UGT enzymes(↑ valproate levels) Erythromycin ↑ Valproate levels Monitor for toxicity
Reduced absorption Cholestyramine ↓ Valproate levels Separate doses by ≥3 hours

References

  1. Sodium Valproate 200mg Gastro-Resistant Tablets – Summary of Product Characteristics (SmPC) – (emc) | 1496
  2. Ritter JM, Flower RJ, Henderson G, Loke YK, MacEwan DJ. Rang & Dale’s Pharmacology. 9th ed. London: Elsevier; 2019. 
  3. SPS 2021. Valproic acid and Sodium valproate monitoring. Published 15 July 2021. Available from: Valproic acid and Sodium valproate monitoring – NHS SPS – Specialist Pharmacy Service – The first stop for professional medicines advice
  4. SPS 2023. Specific medicine switches for solid dose and liquid formulations
  5. Published 13 September 2023 · Last updated 13 February 2026. Specific medicine switches for solid dose and liquid formulations – NHS SPS – Specialist Pharmacy Service – The first stop for professional medicines advice
  6. Up To Date. Antiseizure medications: Mechanism of action, pharmacology, and adverse effects. Last updated: Mar 25, 2026. Accessed from: https://www.uptodate.com/contents/antiseizure-medications-mechanism-of-action-pharmacology-and-adverse-effects?search=valproate&sectionRank=1&usage_type=default&anchor=H1398705747&source=machineLearning&selectedTitle=3~150&display_rank=2#H1398705747 

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