Sodium valproate, Valproic acid, Epilim
Sodium valproate is the drug of choice for treatment of
myoclonic seizures and generalised absence seizures.
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 on ICE
Please state dosage and time of last dose on request form.
Analysed by referral laboratory if specific criteria met.
Most evidence shows that serum monitoring is unnecessary in the
majority of patients on valproate therapy and is potentially
The only indications for measurement are:
paediatric patients at the specific request of a Consultant
patients on 1000 mg/day, whose seizures are not controlled
Patient should be fasting and samples should be collected
before next dose (trough)
Serum in yellow top (SST) tube
Causes for Rejection
Unlabelled or inadequately labelled sample
Target ranges are difficult to define but a suggested range is
50 - 100 mg/L
Symptoms of neurotoxicity (nausea, vomiting, drowsiness) are
increasingly frequent as levels exceed 100 mg/L (700 umol/L)