Pathology Handbook

Valproate

Synonyms

Sodium valproate, Valproic acid, Epilim

Clinical Indications

Sodium valproate is the drug of choice for treatment of myoclonic seizures and generalised absence seizures. 

Drug Kinetics

Valproate has a complex pharmacokinetic profile. It is strongly protein bound to plasma proteins and this binding is concentration dependent so that the free fraction rises (and hence the apparent clearance) at higher concentrations (~ >50 mgl/L). Free fatty acids displace valproate from binding sites and clearance is different in fed and fasting states. This helps explain the wide circadian variation and marked variations in serum concentration (up to 100%) that can occur across the dosage interval.

Request Form 

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Please state dosage and time of last dose on request form.

Availability

Analysed by referral laboratory if specific criteria met.

Specific Criteria

Most evidence shows that serum monitoring is unnecessary in the majority of patients on valproate therapy and is potentially misleading.

The only indications for measurement are:

  • suspected non-compliance

  • paediatric patients at the specific request of a Consultant

  • patients on 1000 mg/day, whose seizures are not controlled

  • overdose

Patient Preparation

Patient should be fasting and samples should be collected before next dose (trough)

Turnaround Time

2 weeks 

Specimen

Serum in yellow top (SST) tube

Volume

2 ml

Container

Vacutainer gold top

Causes for Rejection

Unlabelled or inadequately labelled sample

Target Range

Target ranges are difficult to define but a suggested range is 50 - 100 mg/L

Toxicity

Symptoms of neurotoxicity (nausea, vomiting, drowsiness) are increasingly frequent as levels exceed 100 mg/L (700 umol/L)