Sildenafil (Viagra) was the first oral treatment for ED. It selectively inhibits phosphodiesterase-5 (PD-5), an enzyme that breaks down intracellular cyclic guanosine monophosphate (GMP). This causes smooth muscle relaxation and improves penile blood flow. It is effective in the presence of sexual stimulation but does not cause spontaneous erections or increased libido. Subsequently, the other PD-5 inhibitors, vardenafil and tadalafil, have been introduced. These have a slightly quicker onset of action (about 30 rather than 60 minutes). Tadalafil has a longer duration of action than the others (36 hours).
These drugs are contraindicated in patients with hypotension, recent stroke or MI, severe hepatic impairment, or hereditary degenerative retinal disorders. They should not be co-prescribed with oral nitrates, nicorandil and some antiviral agents. Side-effects of this group of drugs include headaches, flushing and in the case of sildenafil, bluish-green visual disturbance.
These drugs are available on prescription for those with diabetes. Only one tablet per week can be prescribed on the National Health Service, although they can be taken once daily. The lowest dose should be started and increased gradually if ineffective. The tablet is taken prior to planned sexual activity. These treatments are effective in around two-thirds of patients. Apomorphine (uprima) is an alternative non invasive therapy for ED. It is a sublingual preparation that acts centrally on neuronal transmitters in the hypothalamus. It leads to secondary relaxation of smooth muscle in the corpus cavernosum via oxytocinergic pathways. It can be given within 20 minutes of intercourse at a dose of 2–3 mg. Alternative treatments include transurethral alprostadil (MUSE), intracaverno sal alprostadil injections (caverject and viridal), vacuum devices and penile prostheses. These treatments used to be the mainstay of Erectile Dysfunction management but are now rarely used other than in cases of tablet failure. Intraurethral alprostadil (prostaglandin E1) is in the form of a soluble tablet inserted directly into the urethra with an applicator.
Self-administration should only take place after proper training. It should not be used more than seven times during the course of a week. If a partner is fertile then appropriate barrier contraception should be used. Intracorporeal injection therapy is an alternative self-administered technique that was the most popular method of treating ED until recent years. After an initial training period, patients can adjust dose requirements according to response. This should not be given more than three times weekly. Complications include penile pain, priapism and penile fibrosis.
Vacuum tumescence devices are safe and effective but are somewhat clumsy and obtrusive. These devices mostly work on a similar principle. A cylinder is placed over the penis and a connecting pump used to pump air out to create a vacuum. This leads to a tumescent penis. Over the base of the erect penis a rubber ring is placed to maintain the erection. This technique allows an erection sufficient for intercourse in over 80% of patients. They can cause bruising and discomfort and do need to be funded by the patient. Penile prostheses are used for patients who have failed to respond to other therapies. They can be permanent, mechanical or inflatable. Complications are common and include infection, mechanical failure, pain and bruising.
E217 – Diabetes and ED – www.diabetic.today