Patterns of non-adherence to oral antiretroviral medication: frequencies of consecutively missed doses.

Purpose: The therapeutic effect of a once-daily oral drug will be maintained if there are no occurrences of consecutively missed doses that exceed the duration of the drug's effect. The durations of effect of antiretroviral drugs are typically in the range of 1-4 days. Here, we report the observed frequencies of ≥2, ≥3, and ≥4 consecutively missed doses for patients taking a once-daily oral antiretroviral drug for HIV infection.

Patients And Methods: Medication Event Monitoring System (MEMS) data were extracted from an electronic database of MEMS records, for a 30-day period for 555 patients taking once-daily oral HIV drug therapy. We recorded the number of days with missed doses and occurrences of ≥2, ≥3, or ≥4 consecutively missed doses. Distributions of the observed frequencies of ≥2, ≥3, and ≥4 consecutively missed doses as a proportion of number of missed doses were compared to calculated random distributions using the Wilcoxon signed-rank test.

Results: The frequencies of 0, 1, and ≥2 missed daily doses were 0.279, 0.312, and 0.409, respectively. The frequencies of ≥2, ≥3, and ≥4 consecutively missed doses were 0.184, 0.110, and 0.065, respectively. The probabilities that the observed frequencies of ≥2, ≥3, and ≥4 consecutively missed doses were as expected from random chance were =0.345, <0.01, and <0.01, respectively.

Conclusion: Observed runs of ≥3 and ≥4 consecutively missed doses - and hence loss of therapeutic effect for drugs of duration of action of <3 and <4 days, respectively - occurred more frequently than expected if missed doses were randomly distributed.