A 58-year-old man with a 17-year history of HIV is seen for a routine appointment, and he reports difficulty maintaining an erection. Recent laboratory studies showed an undetectable HIV RNA level, a CD4 count of 485 cells/mm³, a normal total testosterone level, and a normal free testosterone level. He is taking elvitegravir-cobicistat-tenofovir alafenamide-emtricitabine. He is requesting prescription medication for erectile dysfunction. The normal dosing range of the phosphodiesterase 5 (PDE5) inhibitors used to treat men with erectile dysfunction are avanafil 50 to 200 mg, sildenafil 25 to 100 mg, tadalafil 5 to 20 mg, and vardenafil 2.5 to 10 mg.