Background: Medication possession ratio (MPR) is widely used as a measure of adherence to antiretroviral therapy (ART). Many adolescents and young adults (AYA) experience ART adherence challenges. Our objective was to determine whether the relationship between MPR and virologic failure (VF) is consistent between AYA and older adults in Nigeria.
Methods: We conducted a retrospective study of AYA (aged 15-25 years) and adults (aged >25 years) who initiated ART between January 2009 and December 2012 at 10 university-affiliated HIV clinics in Nigeria. We used multivariate generalized linear models to assess the relationship between age, MPR (ART doses dispensed)/(days since ART initiation), and risk of VF (HIV RNA >1000 copies/mL) in the 1st year on ART.
Results: The cohort included 1508 AYA and 11,376 older adults. VF was more common in AYA than older adults (30% vs. 24% P < 0.01). Overall, 74% of patients had optimal, 16% suboptimal, and 9% poor adherence (MPR >94%, 80%-94%, and <80%, respectively). AYA attended fewer pharmacy-only visits than older adults (5 vs. 6, P < 0.001). Higher MPR was associated with decreased rate of VF (80%-94%, accounting rate of return 0.57; >94% accounting rate of return 0.43, P < 0.001 vs. MPR <80%). Among those with optimal adherence by MPR, 26% of AYA had VF, a risk that was 20% higher than for older adults with optimal adherence (P < 0.001).
Conclusions: In this Nigerian cohort, MPRs were high overall, and there was a strong association between low MPR and risk of VF. Nonetheless, 26% of AYA with high MPRs still had VF. Understanding the discrepancy between MPR and viral suppression in AYA is an important priority.