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).