Methadone is an orally active opioid used to treat persons with a history of physiological dependence to opioids. Methadone maintenance reduces the risk of death for a heroin addict, but only after stabilisation on a methadone dose. This study reviews the toxicological factors associated with methadone-related deaths.
We have reviewed all methadone deaths that occurred in NSW during 1994 and reviewed and reassessed their manner and causes of death with information on their source of methadone, dose, duration of usage and clinical histories. All cases involved a full toxicological examination and autopsy. Risk analyses were conducted for death with adjustment for age and gender and comparison with a long-term cohort study of heroin addicts.
There were 89 deaths involving methadone in this period. Of these 38 were maintenance patients on a NSW program, 29 used diverted methadone syrup and 18 cases consumed the tablet form (Physeptone). Of the 13 NSW methadone patients who died in the first two weeks of maintenance treatment, at least 10 died from iatrogenic methadone toxicity. The mean (±s.d.) blood level in this group was 0.84 ± 1.4 mg/L. The risk of dying from drug toxicity in the first 2 weeks of a MP was 7-times the risk prior to admission and 84 times the risk later in maintenance at which blood concentration of methadone 0.69 ± 0.43 mg/L. Starting doses range from 30 mg. Another 26 deaths from accidental toxicity were caused by diverted take-home doses of methadone syrup. This group had mean methadone levels of 0.33 ± 0.18 mg/L. There was however a weak correlation between methadone dose and blood concentration.
These data show that toxic methadone concentrations show little difference in the types of methadone associated deaths and that iatrogenic toxicity to methadone is a significant risk for death in the early stages of methadone maintenance programs as is unsupervised use of methadone in opiate-naive persons.