MHRA / CHM Advice (date) Switching between formulations of antiepileptic drugs (AEDs)
For some AEDs there is a need to maintain continuity of supply of a specific product to ensure a consistent
therapeutic effect, whilst for some others switching between formulations is unlikely to have significant clinical
consequences. AEDs have been classified into 3 categories of risk, based primarily on their therapeutic index,pharmaceutical aspects (in particular solubility) and the rate and extent of drug absorption (relates to drugpermeability):
Category 1: phenytoin, carbamazepine, phenobarbital, primidone. Specific measures are necessary to ensure
consistent supply of a particular product (which could be either a branded product or a specified manufacturer's
Category 2: by default AEDs not listed for categories 1 or 3. The need for continued supply of a particular
manufacturer's product should be based on clinical judgement and consultation with patient and/or carer.
Category 3; levetiracetam, lacosamide, tiagabine, gabapentin, pregabalin, ethosuximide, vigabatrin. No specific
measures are normally required and these AEDs can be prescribed generically and without specifying a specific
manufacturer's product .