Treatment-Emergent Mutations and Resistance in HIV-Infected Children Treated with Fosamprenavir-Containing Antiretroviral Regimens

Treatment-emergent mutations and drug resistance were analyzed in virus from HIV-infected children meeting virologic failure (VF) criteria over 48 weeks following treatment with unboosted fosamprenavir or fosamprenavir/ritonavir-containing regimens in studies APV20002 and APV29005. Both antiretroviral therapy (ART)-naïve and ART-experienced patients were enrolled. Patients met VF criteria by either failing to suppress HIV-RNA to <400 copies/mL through week 24 or after confirmed viral rebound (≥400 copies/mL) anytime through week 48. Viral isolates were analyzed for treatment-emergent mutations or reduced drug susceptibility. Through week 48, 25/109 (23%) of APV29005 and 9/54 (17%) APV20002 study patients met VF. VF was more common in ART-experienced patients (68% and 78%, respectively). Major or minor treatment-emergent mutations were detected at VF in virus from 3 patients receiving unboosted fosamprenavir-containing regimens and in virus from 10 patients receiving fosamprenavir/ritonavir-containing regimens across the two studies. Major protease inhibitor mutations and the reverse transcriptase mutation M184V were detected at VF in virus from 4 and 5 patients, respectively, across both studies. Reduced drug susceptibility to any drug emerged in virus from 9 patients at VF, although reduced fosamprenavir susceptibility emerged in virus from only 4 patients (2 ART-naïve and 2 ART-experienced). No cross-resistance to the protease inhibitor darunavir was observed.

In conclusion, given the high proportion of ART-experienced children (71%) in these two studies, the overall incidence of children meeting VF criteria through 48 weeks was relatively low (21%) and development of fosamprenavir reduced drug susceptibility at VF was uncommon, further supporting the use of fosamprenavir-containing ART regimens in HIV-infected children.

HIV protease inhibitors: present and future

Antiretroviral therapy offers many options, largely based on the next-generation protease inhibitors (PIs). Early PI-based treatments involve high pill burdens and dosing schedules, and concerns of long-term toxicities are well established. In patients who have already achieved viral suppression, novel agents and strategies should be used to simplify the dosing treatment, reduce adverse events or preserve drug options. In experienced patients, drug escalation between PIs and different associations between classes allow virological suppression to be reached in the majority of patients. Therefore, there is a persistent clinical need for the discovery and development of new protease inhibitors. Several firms are trying to develop new types of PIs that will not be cross-resistant with existing drugs and will not require ritonavir boosting. This article aims to offer an overview on present drug options recommended for treatment in naive and experienced patients, new strategies currently undergoing clinical evaluation and new compounds in the pipeline.