Drugs suspected to be involved in the DDI-summary
Complete list of drugs taken by the patient
Silodosin 8mg/d atorvastatine 40mg/d paracetamol on demand
Clinical case description
HIV infection diagnosed in 2010, treated by several ART regimens due to different intolerances. DRV/c-FTC-TAF started in 2022 (following intolerance to DTG-3TC) with good tolerance. Some months later, his primary care physician started silodosin 8mg QD due to irritative symptoms of the vessel. Despite the dose exceeding the recommended when it is co-administered with cobicistat, no toxicity was reported. Dose was, anyway, adapted to 4 mg QD in the following HIV visit.
Silodosin is a substrate of CYP3A4 and P-gp, and coadministration with cobicistat is expected to increase silodosin concentrations. Coadministration with ketoconazole (440 mg) increased sidolosin Cmax and AUC by 3.8-fold and 3.2-fold, respectively. Concomitant use of sidolosin with potent CYP3A4 inhibitors is contraindicated (US product label) or not recommended (EU prescribing information). However, given its uroselective effect and wide therapeutic index, silodosin may be used at 4 mg QD (as in this case) with caution and monitoring for side effects such dizziness, of orthostatic hypotension.