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.
The authors wish to acknowledge the work of the New Zealand Coronial Service, and thank the National Coronial Information System and the Victorian Department of Justice and Community Safety for providing access to these data.
Compliance with Ethical Standards
Ethical approval for the study was obtained from the University of Otago Ethics Committee (Reference Number HD16/074) in consultation with the Ngai Tahu Research Consultation Committee. Access to the NCIS was approved by both the NCIS and the New Zealand Chief Coroner.
No sources of funding were used to assist in the preparation of this study.
Conflict of Interest
John Fountain, Andrew Tomlin, David Reith and Murray Tilyard have no conflicts of interest that are directly relevant to the content of this article.
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