As we delve deeper into the mysterious world of prescription drugs and drug approval, we keep coming up with questions that begin with 'How come . . .?' The latest 'How come?' concerns Zonegran (zonisamide), an antiseizure treatment aimed mainly at epilepsy patients.
Manufacturer Elan has just been asked to add a special warning about Zonegran to US doctors after it was found to cause oligohidrosis (an inability to sweat) and hyperthermia, sometimes resulting in hospital care, among patients aged under 16.
Zonegran has been marketed in Japan since 1989 where oligohidrosis and hyperthermia are recognised drug reactions. US approval came 11 years later, but without any special warnings. It was only when similar outbreaks were seen that the drug authorities finally decided to intervene. So 'How come?'
These reactions are being reported in children and young adults aged under 16, yet an Elan director has stated that 'the safety and effectiveness of zonisamide in pediatric patients have not been established, and that zonisamide is not approved for use in pediatric patients.' So how come the drug is being prescribed to children in the first place?
In all, 40 cases of oligohidrosis and hyperthermia have been reported - 38 from Japan and two from the USA. Some cases resulted in heat stroke, but there have been no reported deaths. Elan accepts that the problem is far greater since postmarketing studies are notorious for underreporting the true number of reactions.
Other drug reactions include headache, anorexia, dizziness, confusion, memory loss, agitation, depression, insomnia, somnolence and speech abnormalities.
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