Medicalising the treatment of opioid dependence.

Traditionally the treatment of opioid dependence in Singapore has not been viewed as a public health problem, but rather as a social problem that necessitated custodial and other punitive approaches. The turning point came in 1996, when, after a pilot programme in the Prisons Department, naltrexone was introduced as an option in management of heroin dependence.1 However, because of long-standing attitudes and perceptions held by both the public and the medical profession, ambivalence persisted towards the addict as a patient. Recent advances in neuroscience have increased our understanding of substance-use disorders, and the new insights have important implications for clinical practice. Neural pathways and major receptors have been identified for most drugs of abuse. Many of the biochemical cascades within the brain cell that follow the drug activation of cell membrane receptors have been elucidated.2 Almost all substances of abuse have common effects on the dopaminergic mesolimbic reward system, which extends from the ventral tegmentum to the nucleus accumbens, with projections to the limbic system and the orbitofrontal cortex. Contrary to the view that addicts are weak or bad people lacking will or morals, addiction is now known to be a chronic, relapsing brain disorder characterised by compulsive drug seeking and use.3 In short, prolonged drug use causes pervasive brain changes at the molecular, cellular, structural and functional levels, which persist long after the addict stops taking the drug. Hence, the cue-induced craving and the propensity to relapse.4 There are three medications – apart from adjunctive ones – that are widely used in the treatment of heroin dependence, namely naltrexone, methadone, and buprenorphine. Naltrexone is an opioid receptor antagonist, while methadone is an agonist, and buprenorphine is a partial opioid agonist at the mu opioid receptor and also an antagonist at the kappa opioid receptor. There is insufficient evidence for routine maintenance treatment using naltrexone in opioid dependence.5 Both methadone and buprenorphine are equally efficacious, but methadone maintenance requires high doses to prevent relapses, whereas buprenorphine has a better retention rate.6 Methadone is hardly prescribed locally except for a few elderly opium addicts, because of the concern about its street value as a drug of abuse. Readers should note that, apart from their use for detoxification, neither buprenorphine nor methadone is a “cure” for opioid dependence: both these drugs are substitution agents. However, as maintenance treatment the drugs can help the addict to function better socially and occupationally.7 In spite of the promise of improvement in the lives of addicts with medical care, a distinct trend of buprenorphine abuse has occurred over the past 2 years. Buprenorphine in tablet formulation [proprietary name Subutex (ScheringPlough)] was marketed in Singapore in 2002 as a prescription-only medicine for sublingual administration. Soon afterwards, cases began to appear of the intravenous abuse of Subutex tablets. The intravenous injection of pulverised buprenorphine tablets may produce various physical complications, such as abscesses, human immunodeficiency virus (HIV) infection and hepatitis B or C infections, optic neuritis secondary to infection with Candida albicans, respiratory depression, and tricuspid or pulmonary valve endocarditis. Both intravenous and intraarterial injections of pulverised buprenorphine may cause peripheral limb ischaemia. The consequences of intravascular Subutex abuse are clearly described in 2 papers in this issue of Annals.8,9 Other descriptions of similar complications have been published in local journals of medicine and of epidemiology.10,11 There is a high social cost attached, and a significant demand on healthcare resources to treat and rehabilitate patients with these medical or surgical complications. An additional drawback of buprenorphine is the high degree of drug diversion, as described in the paper by Winslow et al.12 The detailed study by Winslow et al12 is most interesting, as it profiles buprenorphine abusers who seek medical help to escape their situation. It provides strong evidence that the proper selection of patients is one of the most important factors promoting the successful treatment of opioid abuse using buprenorphine substitution.