Synonyms: VPA
Clinical significance
Valproic acid (VPA) is an anticonvulsant widely used to treat the various forms of generalised epilepsy, including absence seizures, grand mal and myoclonic seizures, and partial epilepsies, particularly idiopathic ones. It is also used in some mood disorders (mania, bipolar disorder). VPA acts through several mechanisms that are not fully understood, but this complexity probably explains its broad spectrum of action.
It is quickly absorbed in the intestinal tract and binds almost completely to plasma proteins.
Clinical indications
Monitoring of treatment.
Sample type
The patient must have a blood sample taken
Preparation
You must fast for at least 8 hours; a small amount of water is allowed. You must have been standing or sitting upright for at least 30 minutes. For periodic monitoring of the blood concentration of the medicine, so that results can be compared over time, the blood sample should always be taken the same number of hours after taking the medicine.
Notes
Many medicines can increase or decrease the bioavailability of VPA, above all the other anticonvulsants that may be used together with it to treat epilepsy: phenytoin, carbamazepine and phenobarbital lower VPA levels, while lamotrigine raises them. It is useful to check liver function, blood ammonia, the full blood count and clotting.
Blood levels of the medicine must stay within the therapeutic range (values above 100 micrograms/ml are potentially toxic). There is no close correlation between the therapeutic range and the clinical effect. When the medicine is taken by mouth, bowel disorders (diarrhoea) can reduce its absorption and therefore its blood concentration.