The medication alprostadil is absorbed through the urethra (the tube in the penis through which urine and semen flow) and distributed into surrounding tissues. Unfortunately, only a very small percentage of the total dose actually penetrates the penis, and most of the medication is absorbed into the bloodstream, lessening the direct effect on the penis. The fact that the medication is not placed where it is supposed to act, as opposed to penile injection therapy, explains its lack of efficacy.
The urethral medication (alprostadil) comes in a plastic applicator, is prefilled and ready to use. The physician determines the proper dose. One must insert the prefilled applicator 1.25" into the opening of the penis. A pellet of alprostadil is then pushed out of the applicator into the canal where urine travels.
Since the approval of Viagra, urethral medication use has dropped in popularity. A recent study published in Urology (January 2000) showed that penile injection therapy was more efficacious, better tolerated, and preferred over intra-urethral medication.