Intraurethral suppositories are a specialized drug delivery method where medication is directly inserted into the urethra. This method allows for localized effects within the genitourinary system or systemic absorption into the bloodstream. It serves as an alternative for individuals who may not be candidates for, or prefer not to use, other forms of medication delivery.
Understanding Intraurethral Suppositories
Intraurethral suppositories are small, pellet-like drug formulations designed for insertion into the male urethra. These pellets consist of an active pharmaceutical ingredient combined with excipients, inactive substances that help form the suppository and facilitate drug release. A common medication delivered via this method is alprostadil, often recognized by the brand name MUSE® (Medicated Urethral System for Erection).
This delivery route is primarily employed for treating erectile dysfunction (ED). The alprostadil suppository is inserted using a specialized applicator, allowing the medication to be deposited directly into the urethra. This direct application offers an advantage for some patients, particularly those for whom oral medications are contraindicated or ineffective, or those who prefer to avoid penile injections.
Mechanism of Action
Once an intraurethral suppository containing alprostadil is inserted, the medication begins to dissolve in the small amount of urine remaining in the urethra. This dissolution allows alprostadil to be absorbed through the urethral lining, specifically into the corpus spongiosum, which is the spongy tissue surrounding the urethra.
From the corpus spongiosum, alprostadil is then transferred into the corpora cavernosa, the two main erectile chambers of the penis, through small veins. Alprostadil, a synthetic form of prostaglandin E1 (PGE1), acts as a vasodilator. It binds to specific receptors on vascular smooth muscle cells, activating an enzyme called adenylate cyclase. This activation increases the levels of cyclic adenosine monophosphate (cAMP) within the cells, which subsequently reduces intracellular calcium concentration. The decrease in calcium leads to the relaxation of the smooth muscle tissue in the penile arteries and trabecular tissue, causing these blood vessels to expand and increase blood flow into the penis, thereby facilitating an erection.
Proper Administration
Before administering an intraurethral suppository, empty the bladder by urinating, then gently shake the penis to remove any excess urine. A moist urethra assists in smoother insertion of the applicator. Following urination, hands should be thoroughly washed with soap and water and dried on a clean towel.
To administer the suppository:
- Remove the applicator from its foil pouch.
- Gently stretch the penis upward and outward to its full length.
- Slowly insert the applicator stem, containing the pellet, approximately one inch into the meatus (opening at the tip of the penis).
- Press the button on the applicator to release the pellet into the urethra, holding it in place for about five seconds.
- After removing the applicator, gently roll the penis between the hands for at least 10 seconds while keeping it upright and stretched.
- Sit, stand, or walk for 5 to 10 minutes following administration to aid absorption and allow an erection to develop, which occurs within 5 to 10 minutes and can last for approximately 30 to 60 minutes.
Side Effects and Important Considerations
Common localized side effects include pain or burning sensations in the penis, urethra, or testicles, and redness of the penis. Minor urethral bleeding or spotting can also occur in about 3% of patients, often due to minor abrasions from insertion. Less common side effects include dizziness, light-headedness, headache, back pain, pelvic pain, and flu-like symptoms.
Serious, though infrequent, side effects include symptomatic hypotension (low blood pressure) and syncope (fainting). A prolonged erection (priapism) lasting four hours or more is a medical emergency requiring immediate attention to prevent permanent damage.
Individuals with certain pre-existing conditions, such as urethral stricture, balanitis, severe hypospadias, abnormal penile curvature, acute or chronic urethritis, sickle cell anemia or trait, thrombocythemia, polycythemia, or multiple myeloma, should not use these suppositories due to increased risks. While systemic drug interactions are unlikely given the low systemic absorption, caution is advised when used with antihypertensive medications due to the potential for increased hypotension.
Unopened suppositories should be stored in a refrigerator between 36°F to 46°F (2°C to 8°C), and can be stored at room temperature (68°F to 77°F or 20°C to 25°C) for up to 14 days before use.