Factors predicting 6-month retention among people with opioid use disorders accessing outpatient methadone maintenance therapy in Tshwane, South Africa

Abstract

BACKGROUND. In South Africa (SA), increasing illicit opioid use and associated health challenges can be managed with opioid substitution therapy (OST), such as methadone, if the recommended dose and duration of use are prescribed. The Community Oriented Substance Use Programme (COSUP) provides free methadone to patients with opioid use disorder in Tshwane, SA, on need-based criteria. OBJECTIVES. To determine selected sociodemographic and substance use treatment factors associated with retention for at least 6 months among participants receiving methadone as part of OST in COSUP. METHODS. This was a retrospective cohort study using secondary data of patients treated with methadone at 8 COSUP sites. The factors associated with at least 6 months’ retention for 575 participants from December 2016 to September 2018 were analysed. RESULTS. There were 91.3% males, 86.4% South Africans and 85.9% black Africans, with a median age of 30 years. At baseline, the majority were injecting heroin (55.5%) and were provided with free methadone (59.3%). The median dose of methadone at 6 months or on leaving the programme was 20 mg; 38.4% of participants were retained for at least 6 months. Of those not retained, the median duration on methadone was 56 days, whereas for those retained for at least 6 months, the median number of days on methadone were 254. After adjusting for sex and age, participants receiving methadone doses <50 mg had lower odds of being retained (0 - 20 mg: adjusted odds ratio (aOR) 0.25; p=0.002; 95% confidence interval (CI) 0.10 - 0.61; >20 - 40 mg: aOR 0.20; p<0.001; 95% CI 0.08 - 0.49) than those administered ≥50 mg. Participants who received free methadone had 3.75 the odds of being retained than those buying it themselves (p<0.001; 95% CI 2.47 - 5.70). Participants treated in the inner city had 5.19 the odds of being retained than those in a suburban setting (p<0.001; 95% CI 2.99 - 9.03). Compared with black African participants, white participants had 3.39 the odds of being retained (p=0.001; 95% CI 1.64 - 7.00). Injecting heroin users had 0.63 the odds of being retained (p=0.032; 95% CI 0.41 - 0.96). CONCLUSIONS. To maximise retention on OST, methadone should be free, with maintenance doses >50 mg. Reasons for lower retention among participants from periurban settings, those who inject and those from previously disadvantaged racial groups need to be explored, and findings used to inform programming.