Background The effectiveness of antiretroviral treatment (ART) depends on several factors. Non-adherence is the main cause of treatment failure.

Purpose To evaluate ART adherence in our hospital’s HIV patient cohort and its effect on the efficacy of ART; as well as to determine the effect of several treatment-dependant factors.

Materials and Methods From July to November 2011, all HIV patients taking ART who came to the infectious diseases outpatients were included. Adherence to treatment was estimated as the (percentage) difference between units of medicines that should have been dispensed and units that were recorded in the Pharmacy service as having been dispensed in the last year. The following variables were collected: sex, age, daily number of tablets (T), dose regimen (once daily OD, twice daily TD), ART combination with Nucleoside Reverse Transcriptase Inhibitors (NRTI), Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTI) and Protease Inhibitors (PI/r), adherence and viral load (VL). A patient was considered to be adherent when adherence was *90%. The ART was considered effective when VL was *50 copies/mL.

Results N = 835, 566 men (67.9%), 268 women (32.1%) Mean age = 46.7 ± 8 years Mean Adherence = 92.2 ± 11.3% (* units dispensed/units that should have been dispensed) Adherent patients = 76.3% (No. adherent patients/No. patients) × 100 Mean tablets/day, adherent patients = 3.2 (* no. tablets/day taken by adherent patients/No. adherent patients) non-adherents = 3.7 (This means that non-adherent patients take more tablets/day than adherent patients) Efficacy of ART: 89.5% of adherent patients, 70.1% of non-adherent patients Adherents (%) according to: – · Sex: men = 79.3%, women = 69.8% – · Daily number of tablets: 1T = 81.1%, 2T = 82.4%, 3T = 81.9%, 4T = 74.5%, 5T = 6.9% 6T = 72.2% and >7T = 76.3% – · Dose Regimen: OD = 80.2% and TD = 72.2% – · ART combinations: § 2NRTI+NNRTI = 80.7% § 2NRTI +PI/r = 64.8% § PI/r = 89.4%.

Conclusions The success of the ART is considerably higher in adherent patients (89.5%) than in non-adherents patients (70.1%). Simplifying the ART (OD, fewer tablets) is a strategy able to increase the number of adherent patients. Monotherapy with PI/r improves the adherence to ART.

No conflict of interest.