Evaluating interventions to improve antiretroviral adherence: how much of an effect is required for favorable value?

OBJECTIVE: Uncertainty about the value of antiretroviral therapy (ARV) adherence interventions may be a barrier to implementation and evaluation. Our objective is to estimate the minimum effectiveness required for ARV adherence interventions to deliver acceptable value.
METHODS: We used a validated HIV computer simulation to estimate the impact of ARV adherence interventions on incremental costs and life expectancy. Across a wide range of intervention costs ($1000-10,000, one time or per year), we estimated the smallest effect size compatible with acceptable value (incremental cost-effective ratio < or =$100,000 per life-year). Effect sizes were measured using relative risk (RR) and absolute risk reduction (ARR), and these metrics were applied to nonadherence and nonadherence risk factors. Costs were estimated from a societal perspective ($2003) discounted at 3%.
RESULTS: To give acceptable value, a one-time $1000 intervention must reduce ARV nonadherence by RR < or = 0.82 (ARR > or = 0.04) for moderately nonadherent patients (20% of ARV doses missed) and RR < or = 0.90 (ARR > or = 0.05) for severely nonadherent patients (50% of ARV doses missed). A one-time $5000 intervention has an unacceptable value regardless of effect size for moderately nonadherent patients, and must reduce ARV nonadherence by RR <or = 0.31 (ARR > or = 0.69) for severely nonadherent patients. Interventions aimed at behavioral risk factors (e.g., unhealthy alcohol use) may confer acceptable value (e.g., if < or = $2000 and effect RR < or = 0.71 [ARR > or = 0.29]).
CONCLUSIONS: ARV adherence interventions with plausible effect sizes may offer favorable value if they cost <$5000 one time or per year. ARV adherence interventions with a favorable value should become more integral components of HIV care.