Medicated Urethral System for Erection (MUSE) is a device used to insert an alprostadil suppository into the urethral opening. Eighty percent of the drug is absorbed after ten minutes. Reports of its effectiveness vary from 7 to 65 percent. The most common adverse effects are penile pain, urethral burning, dizziness, and fainting. MUSE also has a very high dropout rate.
What is intraurethral alprostadil (MUSE)?
Intraurethral alprostadil (MUSE) is an intraurethral medication (i.e., injected into the urethra) produced by Vivus (Menlo Park, CA) 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 Viagra, the oral therapy for erectile dysfunction. 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.
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 it may be absorbed at the time of ejaculation, it should not be used with pregnant partners. Men who have undergone prior radical prostatectomy appear to have an increased risk of penile or urethral burning with MUSE and should be warned of this. The exact cause of this is not known; however, there may be 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. 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 and can be associated with serious cardiovascular consequences; thus, MUSE should be used with caution in men with significant cardiovascular risks and in older men. Men who are at increased risk for priapism, such as men 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. Lastly, men with a pregnant partner should not use MUSE.
How does one use MUSE?
MUSE is an on-demand medication and must be taken each time that you wish to achieve an erection. The suppository of the alprostadil is enclosed in a small applicator (Figure 7). One voids before inserting the tip of the applicator into the penis because voiding helps lubricate the urethra. Other topical lubricants, such as K-Y Jelly, Vaseline, and mineral oil, cannot be used because they interfere with the absorption of the alprostadil. Once the applicator is placed into the urethra, the small round button at the end is squeezed, and the suppository is released into the urethra.. Gentle rocking of the applicator from side to side ensures 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. The alprostadil is then absorbed through the urethral tissue and travels via blood vessels into the corpora cavernosa (the erectile tissue of the penis). Once in the corpora cavernosa, the alprostadil stimulates dilation of the arteries and relaxation of the cavernosal smooth muscle within 10 to 20 minutes. The onset of response to the MUSE is quick, usually 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. There are several different doses of MUSE: 125, 250, 500, and 1000 μg. MUSE must be refrigerated.
What is the success rate of MUSE?
In initial studies of MUSE, the success rate was 64%. However, more recent studies have demonstrated its efficacy to be about 30%. Attempts to increase the success rate via the use of a constricting band, the ACT1S venous constrictor, placed at the base of the penis have helped some men. In some men, an erection rigid enough for penetration may occur in the standing position; however, when the man changes to a supine position, the erection decreases. In these men, changing the position used for intercourse or using the constricting band has proved helpful. It is difficult to predict who will and who will not respond to MUSE, and the patient's age and the cause of the erectile dysfunction are not predictive of response. However, MUSE is unlikely to be effective in men who have not responded to intracavernous injection therapy.
What are the side effects of MUSE?
The most common side effect, occurring in one third to one half of men taking MUSE, is pain. The pain may be present in the penis, urethra, testis, or perineum. The intensity of the pain varies, and it depends on the dose taken, meaning that as the dose increases, the intensity of the pain may also increase. Hypotension and syncopal episodes (temporary loss of consciousness due to decreased blood flow to the brain) have been reported in 1.2% to 4% of men, depending on the dose used. Other side effects include urethral bleeding in 4% to 5%, dizziness in 1%, and urinary tract infection in 0.2% of men. Prolonged erections and penile fibrosis (scarring) rarely occur. Ten percent of female partners have vaginal irritation or vaginitis.