Use of Concomitant Medications in HIV-1 Infected Patients in a Large Community Practice in Sydney, Australia

For the majority of patients, management of HIV-1 infection involves effective and well tolerated antiretroviral therapy with simplified pill load and dosing, exemplified by the availability of single tablet regimens (STRs) with single tablet once daily dosing. STR therapy has been shown to improve adherence and reduce hospitalisations (Cohen et al., 2013; Sax et al., 2012). However, the aging of the HIV cohort in Australia and globally has raised issues of increasing co-morbidities and consequent polypharmacy to manage these (Jansson \& Wilson, 2012; Edelman et al., 2013). Polypharmacy may not only impact on adherence, but also increases the potential for drug-drug interactions (Holtzman et al., 2013). Stribild, a highly effective STR, contains cobicistat to boost the levels of the component integrase inhibitor, elvitegravir. Cobicistat does not have antiretroviral activity, but acts by inhibiting Cyp3A4 of the cytochrome p450 metabolic pathway. Other drugs metabolized via this pathway may be affected by this drug-drug interaction (Rogatto et al., 2014). Additionally there is evidence of increased risk of nephrotoxicity with co-administration of tenofovir and non-steroidal anti-inflammatory medication (NSAIDS) (Marcotte et al., 2008). Data on use of concomitant medications in Australian patients with HIV is sparse. This study aims to determine, in a large caseload community HIV practice, the use of concomitant medications in HIV, patient pill load and dosing frequency, and potential drug-drug interactions with stribild.