Adverse reactions to new anticonvulsant drugs

A lack of systematic pharmacoepidemiological studies investigating adverse drug reactions (ADRs) to anticonvulsants makes it difficult to assess accur ately the incidence of anticonvulsant-related ADRs. Most of the available i nformation in this regard stems from clinical trial experience, case report s and postmarketing surveillance, sources that are not, by any means, struc tured to provide precise data on adverse event epidemiology. For various et hical, statistical and logistical reasons. the organisation of structured c linical trials that are likely to provide substantial data on ADRs is extre mely difficult. This review concentrates on current literature concerning serious and life- threatening ADRs. As with the older anticonvulsants, the majority of ADRs t o newer anticonvulsants are CNS-related, although there are several that ar e apparently unique to some of these new drugs. Gabapentin has been reporte d to cause aggravation of seizures, movement disorders and psychiatric dist urbances. Felbamate should only be prescribed under close medical supervisi on because of aplastic anaemia and hepatotoxicity. Lamotrigine causes hyper sensitivity reactions that range from simple morbilliform rashes to multi-o rgan failure. Psychiatric ADRs and deterioration of seizure control have al so been reported with lamotrigine treatment. Oxcarbazepine has a safety pro file similar to that of carbamazepine. Hyponatraemia associated with oxcarb azepine is also a problem; however, it is less likely to cause rash than ca rbamazepine. Nonconvulsive status epilepticus has been reported frequently with tiagabine, although there are insufficient data at present to identify risk factors for this ADR. Topiramate frequently causes cognitive ADRs and , in addition, also appears to cause word-finding difficulties, renal calcu li and bodyweight loss. Vigabatrin has been reported to cause seizure aggra vation, especially in myoclonic seizures. There have been rare reports of o ther neurological ADRs to vigabatrin, such as encephalopathy, aphasia and m otor disturbances. Vigabatrin-induced visual field constriction is the late st and most worrying ADR. Many questions regarding the nature of this poten tially serious ADR remain unanswered, as no prospective controlled study ex amining the phenomenon has been published. Rare cases of behavioural ADRs a nd IgA and IgG2 deficiency associated with the use of zonisamide have been reported. However, relatively few patients so far have been exposed to this drug, and therefore more postmarketing information is required. The relatively late establishment of aplastic anaemia and hepatic failure a s potentially fatal ADRs of felbamate, and of visual field constriction wit h vigabatrin, should serve as ample reminders that ADRs can appear at any t ime.