Predictors of heroin abstinence in opiate substitution therapy in heroin-only users and dual users of heroin and crack.

AIMS

To analyse predictors of heroin abstinence in opiate substitution therapy (OST) based on frequency of crack use and its interactions with other predictors in a clinical non-experimental setting.

DESIGN

Retrospective study.

SETTING

A community drug service in London, UK.

PARTICIPANTS

325 clients starting OST between 2010 and 2014 (197 methadone and 128 buprenorphine).

MEASUREMENTS

Logistic regression models (a general model and separate models for methadone and buprenorphine) assessed demographic and clinical data as predictors of heroin abstinence at one year after treatment start (or at the date of transfer to another service).

FINDINGS

For the general model participants choosing methadone were more likely to use heroin at follow up (OR=2.36, 95% CI: 1.40-3.17) as were daily crack users on methadone (OR=2.62, 95% CI: 0.96-7.16). For the methadone model only daily crack use predicted heroin use at follow up (OR=2.62, 95% CI: 0.96-7.16). For buprenorphine, higher amounts of baseline heroin use, lower buprenorphine dose and daily drinking predicted heroin use at follow up (OR=0.85, 95% CI: 0.75-0.95; OR=1.31, 95% CI: 1.06-1.60 and OR=6.04, 95% CI: 1.26-28.92). Both use of cannabis and depression increased likelihood of heroin abstinence for clients not using crack compared to occasional (OR=6.68, 95% CI: 0.37-119.59; OR=106.31, 95% CI: 3.41-3313.30) and daily (OR=57.49 (95% CI: 2.37-1396.46; OR=170.99 (95% CI: 4.61-6339.47) users.

CONCLUSIONS

Most of the predictors in the general model were found significant only in the buprenorphine but not in the methadone model, suggesting that a general model has little predictive value. Crack use was a significant predictor of heroin abstinence at follow up in all models, however for buprenorphine only when depression or cannabis use was present. Further research is needed to assess effective treatment approaches for the growing population of dual users.