Trends in opiate-related deaths in the United Kingdom and Australia, 1985–1995

Abstract

This paper compares data on rates of opiate overdose mortality in the UK and Australia between 1985 and 1995. Data on rates of ICD 9-coded overdose mortality were obtained from the Office of National Statistics in the UK and from the Australian Bureau of Statistics mortality register. The proportion of all deaths attributed to opioid overdose increased in both countries between 1985 and 1995. The proportion of all deaths attributed to opioid overdose was substantially higher in Australia than in the UK, but methadone appeared to contribute to more opioid overdose deaths in the UK (50%) than in Australia (18%). Given deficiencies in the available data, the reasons for these differences between the two countries are uncertain but a plausible hypothesis is that the greater availability and ease of access to methadone maintenance in the UK contributes to both the lower rate of opioid overdose mortality and the greater apparent contribution that methadone makes to opioid overdose deaths in that country.

Introduction

There are growing concerns in Australia and the UK about an apparent rise in the production of heroin and an increase in its use and the harm caused by its use (Lynskey and Hall, 1998; Parker et al., 1998). One of the major perils of heroin use that appears to have increased is fatal opioid overdose. There has recently been a dramatic rise in the number and rate of fatal opioid overdoses in the Nordic countries (Steentoft et al., 1996), Spain (de la Fuente et al., 1995; Sanchez et al., 1995), Italy (Davoli et al., 1997), Austria (Risser and Schneider, 1994), the US (United States Department of Health and Human Services, 1997) and Australia (Hall and Darke, 1998).

One of the principal treatments for heroin dependence in many countries is methadone maintenance treatment (Farrell et al., 1996). In randomised-controlled trials and controlled observational studies, methadone maintenance treatment has been shown to result in substantial reductions in illicit opioid use and criminal activity (Ward et al., 1998) and to substantially reduce opioid overdose deaths while individuals are enrolled in MMT (Gearing and Schweitzer, 1974; Caplehorn et al., 1994, Caplehorn et al., 1996; Zador et al., 1998a). For example, Gearing and Schweitzer (1974) documented mortality among 17 000 patients receiving methadone maintenance. Findings indicated that the mortality rate among methadone maintenance patients (7.6 per 1000) was similar to that in the general population (5.6 per 1000) but was significantly lower than the mortality rate among those who left the methadone maintenance program (28.2 per 1000) and opioid users not in treatment (82.5 per 1000). Similarly, an Australian study of 307 heroin users enrolled in a methadone maintenance program in the early 1970’s revealed that they were nearly three times more likely to die when they were not receiving methadone than when they were enrolled on the methadone program (Caplehorn et al., 1994).

As with all opioid agonists, overdose deaths can arise in two main ways from the use of methadone for maintenance purposes. For opioid dependent and tolerant individuals, the major overdose risk is during induction onto methadone maintenance. In persons with impaired liver function, normal doses of methadone may accumulate over the first week of treatment to produce toxicity and death (Drummer et al., 1992; Caplehorn, 1998). Persons who exaggerate the extent of their opioid use when being assessed for MMT may be given doses of methadone that prove fatal (Caplehorn, 1998). In Australia, the estimated risk of these deaths is 0.2% per annum of patients inducted into methadone maintenance treatment (Zador et al., 1998a).

Methadone overdose deaths can occur when therapeutically prescribed methadone is diverted and used by non-opioid tolerant individuals. Doses of methadone that are therapeutic in opioid dependent persons may be fatal if used by non-tolerant users. Opioid tolerant individuals, who are unfamiliar with the effects of a longer acting agonist, may overdose when they use it in large doses or in combination with heroin, other opioids and CNS depressant drugs like alcohol and benzodiazepines (Sunjic et al., 1998).

Fatal methadone overdoses occurring as a result of the use of diverted methadone are a potentially more serious public health concern than overdoses occurring in MMT. There are generally many more dependent opioid users who are out of MMT than in it and an even larger number of non-dependent users of opioids (Hall, 1995). With due care, the number of deaths that occur in MMT can be minimised and those that occur accepted as an unavoidable risk run to obtain the considerable benefits of MMT.

Methadone maintenance treatment was established in the UK in 1970 and in Australia in 1969 and subsequently became the main treatment for opioid dependence in both countries. A recent survey of pharmacies estimated that there were 30 000 people enrolled in methadone treatment in England and Wales (Sheridan et al., 1996). They received these services from a variety of agencies including general practice and hospital settings and private and National Health Service (NHS) practices. The National Treatment Outcome Research study (Gossop et al., 1998) indicated that 42.6% of those in treatment for drug dependence were enrolled in methadone maintenance. In Australia there were 19 573 individuals enrolled in MMT in 1996 (Commonwealth Department of Health and Family Services, personal communication) and the majority of those who receive treatment for opiate dependence in Australia are in MMT.

Methadone treatment in the UK differs in several important respects from the model developed by Dole and Nyswander and widely implemented in the US and Australia (Ward et al., 1998). First, any medical practitioner in the UK is permitted to prescribe methadone for the purposes of treating opioid dependence (Farrell et al., 1996). Second, although there are specialist addiction clinics, most UK patients in MMT are given a prescription to be filled by a pharmacist, often for a week or more at a time (Strang et al., 1996). Patients consequently consume their methadone at home rather than under direct clinical supervision, as is the norm in Australian MMT clinics. Third, there is minimal central regulation of MMT in the UK by comparison with Australia. Until 1996, it was compulsory for medical practitioners to notify addicts to an addicts register maintained by the Home Office, but compliance was poor (Strang and Shah, 1985). Fourth, although there are guidelines for MMT, surveys of prescribing practice reveal widespread and unexplained variations between: different geographic areas in the UK (Strang and Sheridan, 1998), general practitioners and psychiatrists; and NHS and private practitioners (Strang et al., 1996). Methadone is also often used for ‘extended’ withdrawal from opiates that blends into de facto maintenance treatment (Gossop et al., 1998).

The aim of this paper is to compare trends in opioid overdose deaths and methadone involvement in these deaths in the UK and Australia, with a view to examining the consequences for opioid overdose mortality of the different methods of delivering methadone treatment in the two countries.