"Urgent action'' needs to be taken over the side-effects of the anti-psychotic drug clozapine, a new study says.
Researchers from the University of Otago, Wellington, and Capital & Coast District Health Board say it is the most effective drug available to treat schizophrenia, but it can have serious adverse effects, according to a study published in the international journal CNS Drugs this week.
They say it causes gastrointestinal hypomotility or "slow-gut'', which can result in severe constipation or bowel obstruction.
All the reported cases of serious clozapine-induced "slow-gut'' in New Zealand and Australia over a 22-year period were analysed, making it the largest international study of the side-effects to date.
One-third of people who are treated for schizophrenia respond better to clozapine than any other medication, but some of its side effects are under-recognised, the study says.
"Official drug safety information in all countries under-estimated the prevalence of clozapine-induced slow gut almost 40-fold and provided almost no information about the range of effects this has,'' lead author Susanna Every-Palmer said.
The study found at least 160 reports of serious clozapine-induced slow-gut, of which 29 patients died, including 13 New Zealanders.
Clozapine slowed the gut in 80% of users in New Zealand, Australia, the United Kingdom and the United States, which "surprised and concerned the authors''.
However, laxatives were found to improve gut motility and reduce the chances of serious harm like bowel obstruction.
The authors were concerned official drug safety datasheets were "completely out of date''.
"If prescribers and users don't know about clozapine's gut-related side-effects, then they don't know they need to prevent slow gut by using laxatives.''
Medsafe says it welcomes the study shedding more light on clozapine.
It was aware of the slow-gut problem and was providing information to prescribers, says general manager Chris James.
"Some information on these effects is already included in the medicine's datasheet - the detailed information about medicines provided for prescribers and updated by the company.''
