A middle-aged Caucasian man living with HIV, clinically stable (viral load <20 copies/mL) on injectable antiretroviral cabotegravir plus rilpivirine every 2 months presented with a 6-month history of bilateral enlargement of the breasts associated with pain. His hormonal profile was normal, and no other underlying cause was identified. He was diagnosed with idiopathic gynecomastia. Tamoxifen is an anti-oestrogen recommended for gynecomastia and has been described in people living with HIV but can potentially induce the activity of cytochrome P450 3A4 (CYP3A4), reducing rilpivirine concentrations, which consequently may cause virological failure and resistance. This is the same for other antiretroviral agents majorly induced by CYP3A4. To date, there have been no reported cases of using anastrozole as a treatment for gynecomastia in people living with HIV or of its co-administration with antiretroviral. We describe the use of an aromatase inhibitor instead of tamoxifen in a person living with HIV, diagnosed with gynecomastia.
Keywords: antiretrovirals; cytochrome P450; drug interactions.
© 2023 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.