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PTD - 314

Test Directory -  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 

Combined Pathology Blood form (Yellow/Black or Blue for GP's). 
Please state dosage on request form.

Availability

Referred test: Analysed by Clinical Biochemistry, Broomfield Hospital, Essex, 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.  Occasionally, levels may be necessary (requested by Consultant Psychiatrists) in establishing whether dose can be increased in patients already receiving high doses (>1500 mg/day). Also, in children under 20 kg where dosage needs to be increased above 20 mg/kg. Requests addressing compliance must be discussed with Consultant Biochemist.

Patient Preparation

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

Turnaround Time

2 weeks 

Specimen

Serum

Volume

2 ml

Container

Red top (plain) tube preferred. Yellow top (SST) tube acceptable if sample separated within 12 hours.

Causes for Rejection

Unlabelled sample

Target Range

Studies show that valproate levels correlate poorly with clinical effect and a target range can be misleading as patients may be well controlled at levels below or above the range. Valproate levels should be interpreted in conjunction with clinical details.

Toxicity

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

Lab. Handling

Processing: Aliquot and store at store at 4C in separating fridge (CB39). Samples left on gel should not be used if they have been left on gel for over 12 hours.
Referral: SVAL & send; VAL & save

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Version 1.0 / September 2014                                                                                                 Approved by: Consultant Biochemist