Client retention in the British Columbia methadone program, 1996-1999

Background: Methadone treatment for heroin addiction has been available for 40 years, but there is relatively little research on the effectiveness of Canadian programs. This paper describes one-year retention among the client cohorts entering the British Columbia Methadone Program during expansion between 1996 and 1999, and examines some factors previously shown to influence retention. Methods: All methadone maintenance prescriptions dispensed to 1996-1999 program entrants were extracted from records of the BC Triplicate Prescription Program. Retention status and covariates were evaluated one year post-entry using logistic regression. Effects of retention status misclassification on time in the program were assessed with a Cox model for clients who received continuous daily dosing or short carries. Results: Fifty-two percent of program entrants were still receiving methadone one year after entry; 24% had left the program at one year but later returned. Age at program entry and average daily dose of methadone were important predictors of continuation. In the logistic regression, only the 1999 year-of-entry cohort appeared to have a different retention trajectory. Year of entry is not a significant predictor of time in the program for those receiving daily or short carry doses only, and other results are consistent between models. Interpretation: Retention rates in the BC Methadone Program are favourable and consistent with published rates. Program expansion does not reduce retention, once the effects of client age and dose are accounted for. Adequate daily dosing appears crucial to both initial retention and return to treatment.