In an indication of how seriously the generic substitution of anti-epileptic drugs (AEDs) issue is now being taken by senior doctors, the American Academy of Neurology last week issued a position statement advocating no substitution of branded AEDs by their generic equivalents without the full knowledge and consent of the patient and their prescribing doctor.

Dr K Liow and his co-authors, writing in the 17 April issue of the journal Neurology, describe epilepsy as unlike other disorders, since it is an all-or-nothing phenomenon. Gradual improvements are not significant for patients; they're either having seizures or they're not. Having a seizure after a period of freedom can have major implications for someone's life that go far beyond their medical condition: apart from the risk of bodily injury to themselves or someone else, losing a driving licence could affect employment, and hence financial and family circumstances. Is it justified, the authors ask, to place patients with epilepsy at undue risk for having a breakthrough seizure in the name of reducing health costs? Isn't it cheaper, in the long run, to give people the more expensive drugs that are known to work?

Healthcare provision in the USA is very different from in the UK. There is no equivalent of the NHS, so all patients must have private medical insurance (though in practice not everyone can afford this). Some insurance plans require pharmacists to dispense the cheapest version of the drug a patient has been prescribed each time the prescription is filled. In Britain, if the doctor does not specify a brand in the prescription, a different generic medicine can be dispensed each time by the pharmacist.

Generic pharmaceuticals contain the same active drug molecule as the branded version, though the other ingredients of the medicine, such as stabilisers, bulking agents, texturing agents, and flavourings, may differ. These can change the speed and degree to which the drug is absorbed and broken down by the body.

Current EU regulations require generic medicines to behave "essentially similarly" in the body to the equivalent branded version, but they don't have to be exactly the same. In the EU, including the UK, the permitted difference is up to 20% above or below the branded version's levels. For most medicines, this is not different enough for patients to notice. For AEDs, however, this is not the case, at least in a minority of patients.

For more about generic medicines and previous research on their use in epilepsy, see Epilepsy Research UK's report on three studies presented at the American Epilepsy Society's 60th Annual Meeting in San Diego, California, last December.

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