What is intraurethral alprostadil (MUSE) and how do I use it?

Intraurethral alprostadil (Vivus's MUSE) is an intraurethral medication (i.e., a drug that is injected into the urethra) that was approved by the FDA in June 1998. Alprostadil is a synthetic form of a normal body chemical, prostaglandin E1, that causes increased blood flow into the penis. MUSE works differently than sildenafil (Viagra), the oral therapy for ED. That is, the prostaglandin in MUSE stimulates the production of a chemical called cAMP, which, like cGMP, can cause the relaxation of smooth muscle and thus increase blood flow to the penis.

MUSE is an on-demand medication, meaning that you must take it each time that you wish to achieve an erection. The suppository of the alprostadil is enclosed in a small applicator (Figure 33). You should void before inserting the tip of the applicator into your penis, because voiding helps lubricate the urethra. Other topical lubricants, such as K-Y Jelly, Vaseline, and mineral oil, cannot be used with MUSE because they interfere with the absorption of the alprostadil. Once the applicator

Figure 33. Muse insertion.

is placed into the urethra, you squeeze the small round button at the end, which releases the suppository into the urethra. Gently rocking the applicator from side to side will ensure that the suppository disengages from the applicator and remains within the urethra when the applicator is removed. Once the applicator is removed, gentle massaging of the penis causes the suppository to dissolve in the urethra.

Once in the penis, the alprostadil is absorbed through the urethral tissue and travels via blood vessels into the corpora cavernosa (the erectile tissue of the penis). There, it stimulates dilation of the arteries and provides for relaxation of the cavernosal smooth muscle within 10 to 20 minutes. The onset of a response to the MUSE is quick, usually occurring within 7 to 20 minutes after it is administered. The duration of the response varies with the dose and ranges from 60 to 80 minutes.

Several doses of MUSE are available: 125,250, 500, and 1000 |ig. This medication must be refrigerated.

Who is a candidate for MUSE?

There are relatively few contraindications to the use of MUSE. Because MUSE is administered intraurethrally and not all of the dose may be absorbed at the time of ejaculation, you should not use this therapy if your partner is pregnant.

Men who have undergone prior radical prostatectomy appear to have an increased risk of penile or urethral burning with MUSE, and they should be warned about this possibility. The exact cause of this side effect is not known, but it may be caused by a postsurgical supersensitivity of the corpora or increased retention of the MUSE in the penis because the dorsal vein may have been tied off at the time of radical prostatectomy. In particular, patients who have experienced pain with alprostadil in the past are likely to experience discomfort with MUSE. Hypotension (low blood pressure) and syncope (fainting) have been noted with MUSE as well and can be associated with serious cardiovascular consequences. For this reason, MUSE should be used with caution in men who have significant cardiovascular risks and in older men. In addition, the use of MUSE requires test dosing in the office to ensure that there is no hypotensive or syncopal event with use. Men who are at increased risk for priapism, such as those with sickle cell anemia, leukemia, polycythemia, thrombocythemia, or multiple myeloma, should not use MUSE. Men in whom sexual activity is not advisable, such as those with severe cardiovascular disease, should not use MUSE.