Viagra, Levitra, Cialis

When a man can't get an erection to have sex or can't keep an erection long enough to finish having sex, it's called erectile dysfunction. Erectile dysfunction is the preferred term rather than the more commonly used term of impotence. Sexual dysfunction is often associated with disorders such as diabetes, hypertension, coronary artery disease, neurologic disorders, and depression. In some patients, sexual dysfunction may be the presenting symptom of such disorders. Additionally, ED is often an adverse effect of many medications.

Although there are a number of options available for non-surgical treatment of sexual dysfunction, it is clear that oral therapy has revolutionized the treatment approach to men with erectile dysfunction.

The FDA approved Viagra in 1998, and it became the first oral therapy for erectile dysfunction on the market. Vardenafil hydrochloride (Levitra) was approved in September, 2003, and Tadalafil (Cialis) was approved in November, 2003. Viagra, Levitra and Cialis work in much the same way. These PDE-5 inhibitors share many similarities, but they have differences as well.

Although sildenafil citrate (Viagra), vardenafil HCl (Levitra) and tadalafil (Cialis) sometimes are called sexual enhancers, they do not directly cause an erection of the penis, but alter the body's response to sexual stimulation by enhancing the effect of the nitric oxide, a chemical that is normally released during stimulation. Nitric oxide causes relaxation of the muscles in the penis, which allows for better blood flow to the penile area.

PDE-5 inhibitors can be used to treat sexual dysfunction caused by high blood pressure, problems affecting nerve function, prostate surgery, side effects of medicines, emotional or psychological ED. Although they work in the similar way, they are not the same in all respects. Sildenafil and vardenafil have similar molecular structures, but tadalafil is structurally different.

Viagra (Sildenafil)

• The success rate of sildenafil amounts to an average of over 80%.
• Onset of action: 30-60 minutes.
• Duration of action: up to 4 h.
• Fatty food is known to delay the absorption of Viagra.
• Contraindicated in persons taking alpha-blockers. (In the current labeling the interaction is considered a Precaution.)
• Vision disturbances are more common after taking Viagra, than after other PDE-5 inhibitors. In July 2005, the FDA found that sildenafil could lead to vision impairment in rare cases and a number of studies have linked sildenafil use with nonarteritic anterior ischemic optic neuropathy.
• The patent on Viagra expires in the early 2012.

Levitra (Vardenafil)

• Vardenafil is more potent and selective biochemically than other PDE-5 inhibitors.
• Onset of action: 25 minutes (the quickest).
• Duration of action is up to 5-6 hours, little longer than that reported for Viagra.
• Not recommended in patients taking type 1A (such as quinidine, or procainamide) or type 3 antiarrhythmics (such as sotalol, or amiodarone).
• The advantage that vardenafil has over sildenafil is that it does not alter color perception, a rare side effect which occurs with sildenafil (because vardenafil does not inhibit phosphodiesterase-6).
• Vardenafil is contraindicated in patients taking alpha-blockers. (In the current labeling the interaction is considered a Precaution.)
• Fatty food delays the absorption of vardenafil. However, it is less sensitive than Viagra to food intake.

Cialis (Tadalafil)

• The most astounding feature of tadalafil is its length of action. It has long half life, which ensures 36-hour duration of effectiveness, allowing for more flexibility and spontaneity in sexual relations. This feature greatly distinguishes Cialis from its two predecessors Viagra and Levitra.
• Onset of action: 16 to 30 minutes.
• Tadalafil is contraindicated in patients taking alpha-blockers.

From a safety perspective, all three Viagra, Levitra and Cialis share similar drug interactions involving CY3A4 inhibitors and a contraindication in the use of nitrates. The side effects are similar for all three PDE-5 inhibitors and include headache, flushing, nasal congestion, and dyspepsia.