Erectile Dysfunction (ED) is a common condition where a man cannot achieve or maintain an erection firm enough for sexual intercourse. While oral medications known as PDE5 inhibitors are often the first treatment, they are not effective for everyone. Intracavernosal Injection (ICI) therapy offers a highly effective, second-line option when oral drugs fail, are poorly tolerated, or are medically contraindicated. This treatment involves directly administering a vasoactive medication into the spongy tissue of the penis to induce a reliable erection. The success rate often exceeds 80% in clinical settings.
Mechanism of Action and Medications
The primary goal of ICI is to induce the physiological process of an erection. The injected medications cause the smooth muscle tissue within the penile arteries and the corpora cavernosa to relax. This relaxation leads to significant vasodilation, allowing a rapid increase of arterial blood flow into the two cylindrical chambers of the penis. As these chambers fill with blood, the pressure expands them, which in turn compresses the veins against the tough outer layer of the penis, a process called veno-occlusion. This compression traps the blood inside, creating the rigidity required for a sustained erection.
The most common medication compounds used are potent vasodilators that must be prescribed and require initial dosage titration by a healthcare provider. Alprostadil, a synthetic form of Prostaglandin E1 (PGE1), is the only single agent approved by the FDA for this purpose and acts by promoting smooth muscle relaxation. Compounded mixtures are also widely used for enhanced efficacy and reduced side effects. Bimix typically combines Papaverine, a smooth muscle relaxant, with Phentolamine, an alpha-adrenergic blocker. Trimix adds Alprostadil to these two compounds, allowing for a lower dose of each drug to minimize the risk of pain or localized side effects.
The Injection Procedure
The injection procedure requires careful attention to sterile technique and specific anatomical considerations. Patients must first wash their hands and clean the medication vial stopper with an alcohol swab before drawing the correct dose into a fine-gauge syringe. Before injection, the patient holds the penis taut and selects an injection site on the side of the shaft.
The medication must be injected into the corpora cavernosum, the spongy erectile tissue, ideally at the 2 o’clock or 10 o’clock position. Patients should rotate the injection site and alternate sides with each use to prevent localized trauma or scarring. The needle is inserted at a right angle (90 degrees) to the skin, and the medication is slowly injected. Immediately after withdrawing the needle, firm pressure must be applied to the injection site for at least 30 seconds to minimize bruising or bleeding. The erection typically begins within 5 to 20 minutes, often requiring sexual stimulation to achieve full rigidity.
Safety and Side Effects
The most significant and serious risk associated with intracavernosal injection therapy is priapism, a prolonged erection that lasts four hours or longer. This condition occurs when the vasoactive medication is overly potent or an incorrect dosage is administered, causing the blood-trapping mechanism to persist too long. Any erection lasting beyond four hours requires immediate emergency medical attention, as delayed treatment can lead to permanent damage to the penile tissue and loss of erectile function. Medical staff often treat priapism by aspirating blood from the penis and injecting reversal agents, such as the alpha-agonist phenylephrine, to restore normal blood flow.
Less severe but more common side effects include a temporary burning sensation or mild pain at the injection site, particularly with Alprostadil formulas. Bruising can occur if the injection hits a superficial vein or if inadequate pressure is applied afterward. With long-term or improper use, there is a risk of developing penile fibrosis, where scar tissue forms within the corpora cavernosum. This scarring can cause penile curvature or angulation, sometimes referred to as Peyronie’s disease, which may necessitate discontinuing the therapy. ICI is generally contraindicated for men with certain blood disorders, such as sickle cell anemia or multiple myeloma, due to an increased risk of priapism, or for those taking blood thinners, which increase the risk of bleeding.