Methadone and Excessive Sweating

Sir—Methadone is recognized as causing the untoward side-effect of excessive perspiration in up to 45% of those prescribed the drug [1]. Medline searches using the terms methadone, morphine, opiates and opioids in conjunction with perspiration, sweating and diaphoresis revealed only one case report of an attempt to treat this problem with biperiden, which proved successful in three patients [2]. The authors postulated that this action was a result of modulation of central thermoregulatory mechanisms. Muscarine is, however, a powerful diaphoretic [3] and it is not surprising that an antimuscarinic would antagonize perspiration through its peripheral action on exocrine glands. Opioids are recognized as potent stimulators of mast cell degranulation and this is thought to be the main mechanism for their diaphoretic action [4]. One might therefore expect an antihistamine to control this common and unwanted side-effect. We treated two patients on methadone maintenance regimens who were complaining of excessive sweating with desloratidine 5 mg per day. This antihistamine is the least likely to cause increases in QT interval and therefore the most appropriate. Both patients were receiving between 50 mg and 90 mg of methadone per day; one patient was male and one female, and one patient had a history of atopy (asthma). Both patients were followed-up after 1 month of treatment and reported that within a day of starting the desloratidine their excessive sweating had stopped. This self-report must, however, be treated with caution, as offering patients treatments which both they and you hope will work can provide a large placebo effect and this treatment was non-blinded. Although the problem of excessive perspiration with methadone is said to be large, affecting up to 45% of methadone treated patients, clinically it does not appear to be a frequent complaint in our practice. There might be many reasons for this, including patients both expecting and becoming accustomed to this side effect and physicians not inquiring as to whether the problem exists. Both this and confirmation of the beneficial effects of antihistamines for this side effect require more detailed study.