Psychosocial determinants of adherence to highly active antiretroviral therapy among injection drug users in Vancouver

Background: Sub-optimal adherence to highly active antiretroviral therapy (HAART) among injection drug users (IDUs) is a significant concern. As such, there is an urgent need to identify psychosocial determinants of adherence that can be incorporated into interventions designed to promote optimal adherence. Objective: To identify psychosocial determinants of adherence to HAART, as well as self-reported reasons for missing doses of HAART among HIV-infected IDUs. Methods: We developed an eight-item adherence self-efficacy scale 'comprised of two sub-scales: adherence efficacy and self-regulatory efficacy. We examined correlates between adherence self-efficacy, outcome expectations, socio-demographic characteristics, drug use and risk behaviours, social support and HAART adherence among 108 HIV-infected participants in the Vancouver Injection Drug Users Study (VIDUS). Pharmacy-based adherence to HAART was obtained through a confidential record linkage to the province of British Columbia's HIV/AIDS Drug Treatment Program. Participants were defined as adherent if they picked-up 95% of their HAART prescriptions. Participants were also asked to indicate reasons for missing doses of HAART. Logistic regression was used to identify the factors independently associated with adherence to HAART. Results: Seventy-one (66%) HIV-infected IDUs were less than 95% adherent. Forgetting was the most frequently cited reason (27%) for missing doses of HAART. Factors independently associated with adherence to HAART included adherence efficacy expectations [OR=1.8 (95% CI: 1.0-3.1); P=0.039] and negative outcome expectations [OR=0.8 (95% CI: 0.7-0.9); P=0.027]. Conclusions: We found low rates of adherence to HAART among IDUs. Psychological constructs derived from self-efficacy theory are highly germane to the understanding of adherence behaviour, and interventions that address these constructs should be developed and tested among HIV-infected drug users.