Pattern and impact of emerging resistance mutations in treatment experienced patients failing darunavir-containing regimen

Background: Ritonavir-boosted darunavir (DRV/r) has proven potent efficacy when used in heavily pretreated patients, harboring protease inhibitor-associated resistance mutations. Limited data are available on resistance pattern emerging in patients failing DRV/r and on subsequent remaining protease inhibitor options. Methods: Analysis of baseline and failure resistance genotypes were performed in patients experiencing virologic failure (>200 copies/ml) after at least 3 months on a DRV/r (600/100 mg twice daily)-containing regimen. Results: Twenty-five highly protease inhibitor-experienced patients were included. Baseline median human immunodeficiency virus type 1 RNA was 5 log 10 copies/ml and number of total-protease inhibitor, major-protease inhibitor and DRV-associated-resistance mutations was 13, 4 and 3, respectively. Median viral replication duration on DRV/r selective pressure was 34 weeks. Emergence of DRV-associated-resistance mutations was observed in 72% (18/25) of patients, at codons L891/M/V (32%), V321 (28%), V111 (20%), 147V/A (20%), 154L/M (20%), L33F/l (16%) and 150V (16%). A high risk of DRV resistance was observed in patients with 2 and 3 baseline DRV-associated-resistance mutations and in patients with more than 24 weeks of ongoing viral replication. According to 2007 ANRS algorithm, isolates classified as susceptible to ritonavir-boosted tipranavir decreased from baseline to failure from 76 to 60% and susceptible to DRV/r from 32 to 12%. Conclusion: Emerging mutations observed after DRV/r failure were those already described to impact the DRV efficacy. Our study provided recommendations to firstly, reconsider lowering the cutoff number of DRV mutations to two; secondly, avoid keeping patients on a DRV-failing regimen for more than 24 weeks and thirdly, to examine the efficacy of using tipranavir after DRV failure.