opinion | SExUAL DySFUNCTioN | in the penis than in other parts of the


body, and so can be used at a lower dose (which will hopefully minimise side-effects). it has a more rapid onset of action than Viagra, although both are recommended to be taken 1 hour before intercourse is anticipated. on the other hand, Cialis is intended for


once daily administration, without regard to the timing of sexual activity or food consumption. it takes up to 2 hours to reach full effect, but remains effective for up to 36 hours.


Treatment side-effects The side-effect profiles of the three products are also broadly similar. The most common are headache, flushing, dyspepsia, and nasal congestion. in addition, Cialis has been reported to cause back pain and muscle aches. The drug has also been found to inhibit a different type of PDE — PDE11 — which is found in skeletal muscle, more than Viagra or Levitra, and this may explain its slightly different side-effect profile. one slightly more worrying suspected


side-effect of PDE5 inhibitors that only emerged after they had been marketed for some time is sudden hearing loss. The US labelling for these products says that the effect may be accompanied by tinnitus or dizziness, and has a temporal relationship to the intake of PDE5 inhibitors, although a direct cause and effect relationship has yet to be confirmed. A study of 47 suspected cases recently published in The Laryngoscope3


found


that the average age of those affected was 56.6 years (although two were as young as 37 years): hearing loss occurred within 24 hours of ingestion of PDE5 inhibitor in two thirds of cases, and 88% of reports were unilateral, with an even left/ right distribution. PDE5 inhibitors act by prolonging the effects of nitric oxide


in the penile vasculature, and therefore should not be used concurrently with drugs that increase the amount of nitric oxide in the body, such as nitrates used in the treatment of heart disease. All three ED products have been shown to increase the hypotensive effect of nitrates, and it is not known how soon after taking a PDE5 inhibitor it is safe to take a nitrate. one of the signs of the success of the


PDE5 inhibitors is the amount of spam email generated urging the recipient to buy such products over the internet. Even assuming that they are not counterfeits, their use without medical supervision is highly inadvisable owing to the risk that they will be used concurrently with nitrates. Furthermore, illicit users of PDE5 inhibitors may also be using other substances to enhance sexual pleasure, such as amyl nitrite (‘poppers’), which also act by producing nitric oxide.


Other pharmacological treatments PDE5 inhibitors are not the only types of drugs used in the treatment of ED. other drug-based treatments include the intracavernous injection of papaverine, a vasodilator that increases blood influx, and medicated urethral system for erection (MUSE), which involves the insertion of a small pellet containing alprostadil


prostaglandin E1


(another name for ) into the urethra. This, too,


has a vasodilatory effect. Apart from the inconvenience of these methods, they are not suitable for everyone. For example, MUSE cannot be used for intercourse with a pregnant woman, as alprostadil may cause uterine contractions. A more recent introduction was


the sublingual apomorphine product developed by Pentech Pharmaceuticals and marketed in Europe as Uprima by Abbott and as ixense by Takeda.


However, it has been withdrawn from


the UK and irish markets, and has not yet been approved in the US. Meanwhile, a new product should


reach the market soon that will offer an alternative to patients who do not like swallowing pills or inserting drugs into the urethra. Vitaros, a cream formulation of alprostadil that is applied externally to the penis, has recently been approved in Canada and has been filed for marketing approval in the US, although the application was originally deemed non-approvable. Developed by the San Diego, California, company Apricus Biosciences, it was launched in China as long ago as 2001. Apricus has a number of licensees lined


up to take over marketing when the product is approved: Warner Chilcott in the US; Bracco in italy; Bayer Schering Pharma for much of the rest of Europe, Australia, the Middle East, New Zealand, Russia and South Africa; and other companies in a range of other countries. The company says that in clinical trials, Vitaros was effective in men with mild to severe ED, including men who did not respond to Viagra. And patients will soon have an even


greater choice of drug treatment. Bayer has recently received approval in the US and EU for an oral dispersible tablet formulation of vardenafil that can be taken without liquid — it will be marketed in the US as Staxyn and in Europe under the Levitra trade name. Furthermore, Global Health Ventures, a company based in Canada, recently received EU approval to market x-Excite, a sublingual formulation of sildenafil, and the Japanese firm Mitsubishi Tanabe Pharma is at an advanced stage of development with avanafil, its own fast-acting, selective PDE5 inhibitor.


Non-pharmacological approaches of course, drugs are only one way to treat ED. A number of types of medical device are also available. The use of devices to manage ED actually has a much longer history than drug treatment. it can be divided into two broad categories: external erection aids and surgical implants. External aids principally comprise vacuum constriction devices, which have been in use for almost 75 years. implants can be divided into two categories: malleable, non-inflatable implants, which


IMAGE SEAN NEL/SHUTTERSTOCK.COM


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