Background Darunavir (DRV) is a high genetic barrier protease inhibitor, which when it is combined with a booster drug such as ritonavir or cobicistat, has shown high effectiveness in wild types such as resistant strains of HIV. The lack of conclusive population studies has determined a consensual cut-off level using the IC50, which in its wild type is 55 mcg/l and in resistant strains is 550 mcg/l.

Purpose To find our TPL of DRV from which below this cut-off we can estimate HVL >20 copies/ml.

Material and methods Our prospective observational study included 51 HIV patients in treatment with the HAART scheme tenofovir disoproxil fumarate +emtricitabine + DRV 800 mg once a day (QD) for at least 4 months, registered previously with some drug-related problem (DRP) (non-compliance suspicion, drug adverse events and persistent or first positive viral loads during HAART scheme). One hundred and twenty TPL were collected and determined by high performance liquid chromatography (HPLC) and with the same samples also were also determined HVL by real-time polymerase chain reaction assay (rtPCR). Patients who needed more than one sample period between sampling were 1 month. We divided all the TPL in two groups, where 1000 mcg/l was a random cut-off. In each group, we established the proportion of patients with HVL >20 copies/ml.

Results Twenty-six samples were included in group 1 (TPL <1000 mcg/L) and 94 in group 2 (TPL >1000 ng/ml). Samples related to HVL >20 copies/ml were 23 from group 1 (88.5%) and 58 from group 2 (61.7%). The proportional difference between this high HVL in both groups were statistically significant (Chi-square test p<0. 05). The relative risk to have HVL >20 copies/ml was 1.43 (95% CI: 1.16 to 1.77) in favour of group 1.

Conclusion Patients with TPL <1000 mcg/L could have a major risk of therapeutic failure measured by HVL >20 copies/ml. We need to increase the size of population in this study to confirm this cut-off.

No conflict of interest