Specimens must be collected at least 8 hours after last dose, preferably just before next dose e.g. delay morning dose until after morning blood collect.
Quoted therapeutic ranges refer to trough levels
There is no relationship between serum concentration and therapeutic response.
The only indications for measuring sodium valproate are to check compliance or to investigate toxicity.
Indications for monitoring anticonvulsants vary between the different drugs.
The therapeutic range is a guide only. Levels below the range may control seizures; levels above the range may not be toxic and may be necessary for control.
When changing doses, retesting should be delayed a week or so till a new equilibrium develops.
Phenytoin, carbamazepine and phenobarbitone are potent inducers of hepatic enzymes thereby raising serum levels of GGT and ALP.
The raised enzymes are regarded as an acceptable side-effect.
Primidone (qv) is measured as phenobarbitone which is the active metabolite.
Fosphenytoin cross reacts with the phenytoin assay, it is recommended that samples for serum phenytoin measurements be collected at least 2 hours after an intravenous dose of fosphenytoin and at least 4 hours after an intramuscular dose.
Local / (Valporate Referred test)
Can be added on to an existing request up to 5 days following sample receiptSpecimen Labelling Procedure