Editor, – The author of 'Drug treatment for opioid dependence' (Aust Prescr 2001;24:4-6) refers to the term dependence as if there is only one possible meaning. However, there are two forms of dependence. One is where the opioid receptors require an opioid to prevent withdrawal effects - physical dependence - and the other is a psychological dependence whereby illicit opioid users use opioids but are not physically dependent. It is acknowledged that most, if not all, physically dependent people would have been psychologically dependent at some stage and may still be so. Which group is the author referring to? Does the author imply that there are 70 000 heroin users that are physically dependent or are some of these users not physically but psychologically dependent?
Our research into methadone reveals a wide and unpredictable half-life ranging from as little as four hours to as long as four days. The author states that methadone for maintenance need only be given once a day. This does not correlate with the variable half-life of methadone and may be one of the reasons that methadone given once a day fails in about 15% of patients. If the half-life is short, it would be possible to treat that person with a large once-daily methadone dose but from a pharmacological perspective they may well do better with a smaller dose given more frequently, more in line with the half-life of methadone. From the practical perspective this equates to twice daily. This approach has been verified when using methadone for pain control.
Associate Professor D.A. Cherry and
Associate Professor G.K. Gourlay
Pain Management Unit
Flinders Medical Centre
Bedford Park, SA
Dr Alex Wodak, author of 'Drug treatment for opioid dependence', comments:
Professors Cherry and Gourlay argue that physical and psychological forms of drug dependence should be considered separately. While contemporary definitions of 'drug dependence' by reputable authorities abound, most now regard the physical and psychological components of drug dependence as inseparable. The operational definitions used today are mainly derived from the DSM-IV and ICD-10 classifications of diseases. The estimate of more than 70 000 severely dependent heroin users in Australia was based on a unitary rather than a dualistic notion of drug dependence.
The wide variation in methadone plasma half-life, rightly emphasised by Professors Cherry and Gourlay, seems more of a problem for analgesia than for the management of heroin dependence. Even if twice-daily administration was preferable for methadone treatment, the need for supervised administration for the vast majority makes this option logistically unfeasible. Twice-daily supervised methadone administration does have a role for a small minority. For the vast majority of heroin-dependent persons seeking help, methadone treatment achieves substantial benefits with few adverse effects.
