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Warning on switching epilepsy generics

Variation in generic formulations can endanger patients

Louise Prime

Friday, 01 July 2011

Switching between generic anticonvulsants may sometimes endanger patients, warn researchers.

Their study, published early online in Annals of Neurology, found that most generic antiepilepsy formulations provided total drug delivery similar to that of reference (branded) products. But differences in peak concentrations were common, which could allow breakthrough seizures to occur when patients’ anticonvulsants are switched, especially between different generics.

US researchers at Johns Hopkins University caution that because keeping blood concentrations of drugs within a narrow range can be critical in epilepsy, the differences they found between generic formulations and branded medicines could lead to dangerous under- and overdosing.

The US Food and Drug Administration states that generic products in general must have a peak blood concentration and total amount absorbed that is 80-125% of the branded product, which the study’s authors say is safe in most therapeutic areas.

They compared bioequivalence data provided to the US Food and Drug Administration for 141 generic formulations of anticonvulsants and found that most generics differed by less than 15% from their branded equivalents.

However, some generic anticonvulsant formulations, in particular oxcarbazepine, fell near the lower edge of the acceptance limit, while others were close to the upper limit – meaning a potential 30% difference between generic formulations.

The researchers warn that their results mean that generic prescribing in epilepsy could prove unsafe for patients.

“Overall, generics should be used for treating epilepsy,” they say. “However, we suggest that patients and pharmacies should be cautious when switching between different generic version of anticonvulsants, and policy makers should evaluate whether standards that set the range for generics’ similarity to brand name versions are appropriate for every drug. For patients with epilepsy, that may not be the case.”

They add that similar problems with switching generics could occur in other disease areas in which the dosing window is narrow, such as chemotherapeutics for cancer.

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