How long is the window of opportunity between adherence failure and virologic failure on efavirenz-based HAART?

Purpose: The time between onset of nonadherence and onset of virological failure is unknown. However, this information is critical to the design, implementation, and testing of interventions aiming to forestall treatment failure. Method: We conducted an observational cohort study of 116 HIV-infected adults with virological suppression on efavirenz-based regimens. Patients were seen monthly and censored at virological failure (<1000 copies/mL) or 12 months, whichever came first. Adherence was measured using the Medication Event Monitoring System (MEMS). Percent of doses taken was summarized for 90-day periods. We assessed 4 adherence periods: immediately prior to censor, and then 30 days, 60 days, and 90 days prior to censor. Results: Adherence was significantly lower for patients with virological failure (n = 7) than those without virological failure (n = 99) at all time points assessed. These differences were statistically significant even up to 90 days prior to the virologic failure date (failure group 57% vs. nonfailure group 95%; p = .03). Conclusion: The window between the onset of nonadherence and virological failure can be as long as 90 days. This will allow substantial time for interventions to be implemented and to take effect.