Alprostadil, the synthetic formulation of PGE1, is the only pharmacologic agent approved by the FDA for the management of ED via intracavernous and transurethral routes. Alprostadil stimulates adenyl cyclase to increase intracellular levels of cAMP, lowering intracellular concentrations of calcium, thus relaxing arterial and trabecular smooth muscle. Drug is transferred from urethra to corpus spongiosum to corpus cavernosum. MUSE (medicated urethral system for erection) consists of a very small semisolid pellet (3 × 1 mm) administered into the distal urethra (3 cm) by a proprietary applicator (_{MUSE VIVUS Inc, Menlo Park, CA}).

Clinical trials showed that 66% of men responded to an in-office trial; of these, 65% had successful intercourse at least once at home with MUSE, for a rate of 43% (_{Padma-Nathan, 1997}). With MUSE therapy, the rigidity can be enhanced by an elastic ring placed at the base of the penis (ACTIS, Vivus Inc), to mechanically assist veno-occlusion (_{Lewis, 1998}).

Penile pain is a ubiquitous side effect of alprostadil-based therapies and is clearly dosage-related; in MUSE patients the discomfort can include a dull ache in the penis and the scrotum. The reported penile pain rate was 33% in MUSE trials. Hypotension and syncope have been noted in 1-5.8% of patients, thus mandating that initial administration be in the office setting.