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Who is a candidate for penile injection therapy?

Because the injection requires manual dexterity, it is important that the man be able to perform self-injection.

In some men for whom giving an injection may be difficult or who are anxious about pushing the needle into the side of their penis, an autoinjector is available that makes this task easier. Another option is to have the man's partner perform the injection. Similarly, if the man is obese and has trouble seeing his penis, self-injection may be difficult, so he would need to enlist the aid of his partner.

If a man has tried MUSE in the past and has experienced significant discomfort with it, then using Caverject or Edex will merely cause further discomfort. In this situation, it would be more appropriate to try triple P. In addition, if the man has a known hypersensitivity or has had a prior reaction to prostaglandins, then Caverject or Edex would not be appropriate. Depending on the severity of the reaction, however, the man might consider using bimix (papaverine and phentolamine only).

In a number of conditions, injection therapy may potentially produce additional side effects. For example, men who are prone to priapism, such as those with sickle cell disease or trait, multiple myeloma, and leukemia, are at increased risk for priapism if they use injection therapy. Men with Peyronie's disease should be aware that the process of injection causes local trauma to the tunica albuginea, which could theoretically cause new plaques to form. Men who are taking blood thinners, such as warfarin (Coumadin), can use injection therapy, but should apply pressure to the injection site for a minute or so to prevent a bruise. Men who are taking a monoamine oxidase inhibitor (an older type of antidepressant), such as Marplan, Nardil, Phenelzine, or Parnate, should not use this therapy.

What is the success rate of penile injection therapy?

Success rates for intracavernous injection therapy range from 70-94%. This kind of treatment is helpful in ED of all causes. Although injection therapy does not interfere with orgasm or ejaculation, its long-term success requires that the individual be comfortable with the injection process. Besides its overall success rate, another advantage of injection therapy is its quick onset of action, within 5 to 20 minutes of injection.

The dose required to achieve a successful erection varies greatly with the cause of the erectile dysfunction. Young men with spinal cord injury may require only 1 |ig of Caverject or Edex, whereas older men with vascular disease and diabetes may require 40 |ig of these medications.

What are the risks of penile injection therapy?

Despite the high efficacy and relatively benign side-effect profile of injection therapy, there is a high discontinuation rate with this treatment for ED. A recent review demonstrated that 15% of men who are offered injection therapy do not even try it, 40% discontinue treatment within 3 months, and only 20-30% of men continue with injection therapy for more than 3 years. Reasons for discontinuation include fear of needles, the injected volume, adverse effects, partner discontent with this mode of therapy, loss of partner or relationship issues, problems with the ability to administer the medication, and the return of spontaneous erections. Other side effects include: (1) pain—injection site-related or diffuse, (2) hematoma—increased risk in men taking blood thinners, (3) priapism, (4) penile fibrosis—scar tissue within the corpora which may lead to a need for a higher dose of medication, (5) plaque formation— palpable scar tissue at the site of needle penetration of the corpora. The risk of liver injury with injection therapy is low and does not appear to be a concern for men using Caverject or Edex.

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