indications for monitoring/checking drug levels of antiepileptics
Last edited 08/2018
NICE (1,2) state that:
- in adults - regular blood test monitoring in adults is not recommended as routine, and should be done only if clinically indicated
- in children - regular blood test monitoring in children is not recommended as routine, and should be done only if clinically indicated and recommended by the specialist
- indications
for drug levels:
- detection of non-adherence to the prescribed medication
- suspected toxicity
- adjustment of phenytoin dose
- management of pharmacokinetic interactions
- specific clinical conditions, for example, status epilepticus, organ failure and pregnancy
- examples of
blood tests include:
- before surgery - clotting studies in those on valproate
- full blood count, electrolytes, liver enzymes, vitamin D levels, and other tests of bone metabolism (for example, serum calcium and alkaline phosphatase) every 2-5 years for adults taking enzyme-inducing drugs
- asymptomatic minor abnormalities in test results are not necessarily an indication for changes in medication
Note that the timing of drug level sampling is critical, and should always be indicated on the request form. Particularly important are:
- whether a trough or peak is being measured
- bloods taken at the time of symptoms
Drug levels are interpreted in the light of therapeutic ranges; however it must be remembered that ranges are a statistical statement and the context of the individual must be bourne in mind.
Reference: