Nonmedical use of promethazine hydrochloride among heroin injectors in vietnam: Unrecognized risks and unintended consequences

Background: Surveillance studies have noted intravenous injection of promethazine hydrochloride (PHC) among populations that use heroin in south and southeast Asia. However, little is known about onset and initiation of PHC use and its relationship to habitual heroin use. Methods: As part of a longitudinal study of heroin initiation, a sample of 179 new heroin users, aged 15-27 years, were interviewed between October 2005 and December 2006 in Hanoi, Vietnam. Cox proportional hazard regression analysis was used to characterize age at promethazine initiation and its association with relevant covariates. Results: 76% reported lifetime use of PHC. Mean age of PHC initiation was 21.3 years, on average 6 months following onset of heroin injection. In multivariate analysis, lifetime use of diazepam [HR = 1.69 (1.17, 2.44); p-value = .01] and injecting heroin for more than 1.58 years [HR = 1.46 (1.04, 2.06); p-value = .03] were associated with PHC initiation. Conclusion: Intravenous injection of PHC is a relatively common practice among young injection heroin users in Hanoi, Vietnam who use it on a situational basis to substitute for heroin (when heroin is not available or when heroin is too costly) or to augment the effects of an inadequate heroin dosing (delaying onset of heroin withdraw). Existing drug prevention strategies in Vietnam are focused primarily on heroin and most new heroin users initiate PHC use without prior knowledge of its high risk for serious vein damage. Future research is needed on the PHC use among heroin users, including long-term medical consequences of PHC exposure.