Viagra ( Sildenafil )
Boston University Medical Campus
Ricardo Munarriz, MD
The most common sexual dysfunctions in men include lack of interest, premature ejaculation and erectile dysfunction. The latter affects 52% of men between the ages of 40 and 70, including mild, moderate and complete forms of ED.
Organic or physical causes for sexual dysfunction in men include vascular, hormonal and neurologic factors. Concerning vascular causes, the risk factors for atherosclerosis (including smoking, high blood pressure, diabetes (diabetics do not respond well to pills like sildenafil (Viagra)) and high cholesterol are ALSO risk factors for erectile dysfunction. Since a straddle injury or use of a narrow saddle can obstruct and impair arteries to the penis, bicycle riding is also considered a risk factor for erectile dysfunction.
Little attention has been paid to endocrine factors. Testosterone modulates desire, arousal and orgasmic function. Concerning the orgasmic response, testosterone modulates the integrity of genital sensory receptors. Concerning the arousal response, decreased testosterone blood levels can influence the efficacy of sildenafil (Viagra). If the sildenafil response is not reliably improving erection, the physician should first check if the patient is taking the pill correctly. The physician should also check the patient’s testosterone level. One investigator in Italy gave testosterone to patients with low testosterone who did not respond to sildenafil (Viagra). When daily testosterone was given, subsequent sildenafil (Viagra) use resulted in IIEF (the International Index of Erectile Function questionnaire used to determine erectile function) scores improving significantly.
Other risk factors for erectile dysfunction include neurologic problems (multiple sclerosis, stroke), depression and medications for treating diabetes, hypertension, heart disease and depression.
There are many oral therapies for erectile dysfunction, but the only approved medication in the US is the PDE 5 enzyme inhibitor sildenafil (Viagra). Unapproved therapies, some of which are available in the US and some elsewhere, some of which have data to prove efficacy and some not, include tadalafil (Cialis), vardenafil (Levitra), yohimbine, phentolamine, trazodone, apomorphine and neutraceuticals. PDE5 inhibitors act to relax penile erectile tissues with sexual stimulation thus enhancing your ability to get an erection. Sildenafil (Viagra) is effective for all sorts of erectile dysfunction in 69% of people. Why is there a need for another pill? In some cases the erection is not hard enough, sometimes sildenafil (Viagra) just doesn’t work.
Structurally vardenafil (Levitra) is similar to sildenafil, while tadalafil (Cialis) is very different. Vardenafil (Levitra) is almost 10 times more biochemically potent than sildenafil, therefore a lower dose is needed to facilitate the penile erection, potentially resulting in less side effects. Selectivity is the ability of the drug to attach to the specific enzyme PDE 5 found in penile tissues. Vardenafil (Levitra) is more selective than sildenafil and tadalafil (Cialis) to PDE5, which again means a lower dose is needed with potentially less side effects. Tadalafil is very specific for PDE5 and is also very specific for the enzyme PDE11. Unfortunately, we don’t know much about PDE11, which is found in the heart, in the pituitary gland in the brain and in the testicles. Pharmacokinetics, half-life, is how long the medication stay s in the blood. Sildenafil (Viagra) has a half-life of 4 hours and vardenafil (Levitra) has a half-life of 4-6 hours while tadalafil (Cialis) has a half-life of 17.5 hours. This means that vardenafil (Levitra) should act longer than sildenafil (Viagra) but the clinical significance is not known. Tadalafil (Cialis) has the longest half-life and allows you to take the medication and not relate the sexual activity to the immediate use of the medication. The drawback is if you need nitrates after using tadalafil (Cialis), this medication lasts a long time in your blood stream and may place you at a higher risk. Younger people might do well treated with tadalafil, (Cialis) while older people with other health issues might be better off using sildenafil (Viagra) or vardenafil (Levitra) but more data are needed. The side effects of vardenafil (Levitra) are potentially less than sildenafil (Viagra), but more data are needed. In a recent study on men with erectile dysfunction and diabetes, vardenafil (Levitra) improved their erectile dysfunction. Tadalafil (Cialis) is as effective as sildenafil (Viagra), and vardenafil (Levitra) with similar side effects except for back pain that occurs occasionally with tadalafil, probably because of the long half-life.
Many people stop taking drugs because they are experiencing side effects, they no longer have a partner, or they are worried about safety. Sexual activity is not a major contributor to the risk of a heart attack. Sexual activity, with or without sildenafil (Viagra) increases the chance of an MI during sexual activity by only 0.1%. If pills fail, there are vacuum devices, Muse, injections, bypass surgery and implants.
The patient making a presentation has had penile bypass surgery. In addition he takes testosterone and sildenafil as needed.. This is a classic example of why people with ED need complete care: a psychological exam, history and physical exam, and diagnostic studies with long term follow-up care. Patients with ED should not just be prescribed sildenafil (Viagra) and then be lost to follow-up.