INTRODUCTION
Gynecomastia is caused by an imbalance in oestrogen and testosterone levels, which results in a high oestrogen to testosterone ratio. It can occur physiologically during the neonatal period, puberty, and in older men above 50 years (prevalence 36% to 57%), as well as in pathological circumstances(1). In HIV, the prevalence of gynaecomastia ranges from 1.8% to 3% and is associated with androgen deficiency or the use of some antiretroviral drugs, including efavirenz, stavudine and didanosine(2,3).
Tamoxifen is a selective estrogen receptor modulator and has traditionally been the go-to therapeutic option for managing gynecomastia(4,5). In this case, tamoxifen could potentially induce the activity of cytochrome P450 3A4 (CYP3A4), reducing rilpivirine concentrations, which may cause virological failure(6). According to the national health service (NHS) guidelines in the UK, an aromatase inhibitor can be used in place of tamoxifen(7). To our knowledge, this is a first case report highlighting anastrozole as a therapeutic option for gynecomastia in a patient on a non-nucleoside reverse transcriptase inhibitors (NNRTI) accounting for potential drug drug interaction (DDIs).