"Urgent action" needs to be taken over the side effects of an antipsychotic drug clozapine, a new study says.
Researchers from the University of Otago, Wellington, and Capital & Coast District Health Board say it has 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.
However, they're mostly concerned about the dozen or more New Zealanders who've died from it.
All the reported cases of serious clozapine-induced 'slow-gut' in New Zealand and Australia over a 22 year period were analysed, making this the largest international study of these side effects to date.
One-third of people who're treated for schizophrenia respond better to clozapine than any other medication.
Some of its side effects are under-recognised, the study shows 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, Otago University's Susanna Every-Palmer, says
The study found at least 160 reports of serious clozapine-induced slow-gut, of which 29 patients died, including 13 New Zealanders.
Serious harm from clozapine-related slow-gut is preventable, Dr Every-Palmer says, but more research is needed.
Clozapine slowed the gut in 80 percent of users in New Zealand, Australia, the UK and USA which "surprised and concerned the authors".
However, laxatives were found to improve gut motility significantly and reduce the chances of serious harm like bowel obstruction.
"While Medsafe has issued a number of prescriber updates on this issue, the manufacturers' official drug safety datasheets are completely out of date," Dr Every-Palmer says.
"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."
Concerns of slow-gut shouldnt' stop people from taking clozapine, however, as it can be "very effective'', co-author Professor Pete Ellis says.
Medsafe said it welcomes the study, as it "helps provide a clearer picture of the additional steps needed to be taken to allow Clozapine to be appropriately used", general manager Chris James says.
It admits there are some significant adverse reactions associated with treatment that require close monitoring, and is aware of potential gastrointestinal issues, including hypomotility.
It says it's provided advice and updates to prescribers about this.
"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," Mr Jones says.