Fatal Toxicity Indices for Medicine-Related Deaths in New Zealand, 2008-2013

The fatal toxicity index (FTI) is a measure for assessing the relative risks of death due to the medicines prescribed in a population. This knowledge is useful for prescribers and informs medicine safety initiatives. This study aimed to calculate FTIs for the New Zealand population using three methodologies.

New Zealand coronial data describing medicine-related deaths from 1 January 2008 to 31 December 2013 were retrospectively extracted from the National Coronial Information System. Three fatal toxicity indices were derived using the number of deaths attributed to each pharmaceutical as the numerator and the total defined daily doses, number of patients and number of prescriptions as denominators.

There were 703 medicine-related deaths, of which 627 were assessed as due to one primary contributor. Median decedent age was 48 years (interquartile range 37-58), and 319 (51%) were male. Deaths were intentional in 252 cases (40%), unintentional in 284 (45%) and unknown in 91 (15%). The majority of deaths (n = 486, 78%) occurred in the community. Opioids, antidepressants, antipsychotics and hypnotic-anxiolytics caused most fatalities. While the FTIs for individual medicines varied by denominator applied, methadone and clozapine fatalities were prominent in all three indices. The antidepressants clomipramine, dosulepin and doxepin consistently returned the highest FTIs in their group.

New Zealand prescribers should be aware of the high relative risk of death associated with methadone and clozapine; that clomipramine, dosulepin and doxepin were identified as the most dangerous antidepressants; and that zopiclone carries a similar fatal risk to benzodiazepines. Varying results were found between the FTIs calculated, making comparisons, particularly between populations, difficult.