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Male sexual dysfunction is one of the most common health problems affecting men more often with increasing age. Chronic ED affects about 5% of men between the ages of 40 and 15-25% of men aged 65 years. Transient ED and inadequate erection affect as many as 50% of men aged 40 to 70.

About 95% of cases, appropriate treatment can be found. Erectile dysfunction can be treated at any age, and awareness of this fact is growing. More men seeking help and returning to normal sexual activity because of improved, successful treatments for erectile dysfunction.

Viagra, Levitra and Cialis

Currently, there are three oral drugs approved by the Food and Drug Administration (FDA) for treatment of erectile dysfunction: sildenafil (Viagra), vardenafil (Levitra) and tadalafil (Cialis). All these agents block the enzyme phosphodiesterase type 5 (PDE-5) and belong to a class of drugs called phosphodiesterase (PDE) inhibitors.

Viagra was the first and probably the most famous of the three PDE-5 inhibitors used to treat erectile dysfunction. Viagra was approved as an effective means for treating erectile dysfunction in the March 27, 1998. Production Viagra Pfizer, Inc

Levitra was the second PDE-5 inhibitor to come to market in the United States, and it was approved by the FDA in August 19, 2003. Levitra is the production of pharmaceutical company Bayer.

Cialis was the third PDE-5 inhibitor to come to market, and was approved by the FDA at the end of November 21, 2003. Cialis production Lilly ICOS LLC.

The main advantage of PDE-5 inhibitors is that they do not cause erections at inappropriate times because they act only in response to sexual stimulation. If there is no sexual stimulation drug remains in the background. All three are taken orally prior to planned sexual activity, acting to increase blood flow to the penis in response to sexual stimulation. However, there are important differences between these three, the differences that may affect the safety, specificity, duration, side effects, and ultimately, public recognition in this class of drugs.

Mechanism of action

PDE-5 inhibitors do not directly cause penile erection, but they alter the body's response to sexual stimulation by enhancing the effects of nitric oxide, a chemical that is usually released during stimulation. Nitric oxide causes weakening of the muscles of penis, which allows better blood flow to the genital area.

The effectiveness of PDE-5 inhibitors

All 3 PDE-5 inhibitors have demonstrated excellent performance. Viagra, 84%, slightly more effective than 81% on Cialis and Levitra to 80%.

Dosage forms, the onset of action and duration of effect

Viagra and Levitra differ only slightly from the standpoint of their structure, while Cialis is markedly different from Viagra and Levitra in their molecular structure, which is also reflected in pharmacokinetic differences.

Viagra: 25 mg, 50 mg 100 mg tablets

• Onset of action: 30 minutes (effect delayed if taken with food)
• Duration of action: from 4 to 5 hours

Levitra: 2.5 mg, 5 mg, 10 mg, 20 mg tablets

• Onset of action: 25 minutes (effect delayed fatty foods)
• Duration of action: from 4 to 5 hours

Cialis: 5 mg, 10 mg, 20 mg tablets

• Onset of action: 16-45 minutes (the effect is not delayed by food)
• Duration of action: 36 hours

All three drugs require sexual stimulation to be effective. Viagra should be taken on an empty stomach works better if you do not eat high-fat diet around the time you take it. Levitra may be slightly less effective if you eat high-fat diet, but a moderate-fat diet does not reduce its effectiveness. Cialis works without regard to what you eat. Viagra and Levitra have similar half-lives, and beginning and duration of action. Cialis has a slow onset of action and longer duration of action due to its half-life.

Patients who want to spontaneity can choose Cialis, which can allow for successful intercourse up to 36 hours postdose, although it takes longer to reach peak effect. Significantly longer than the effect for Cialis, likely would reduce the dosage and more impulsivity among partners, but can potentially extend the side effects.

Dosage

The recommended dose for Viagra is 50 mg, and the physician may adjust this dose to 100 mg or 25 mg, depending on the patient. The recommended dose for either Levitra or Cialis is 10 mg, and the physician may adjust this dose to 20 mg if 10 mg is insufficient. Low dose of 5 mg for patients who were taking other medications or conditions that may reduce the body's ability to use the drug. Levitra is also available in 2.5 mg. None of these PDE-5 inhibitors should be used more than once a day.

Possible side effects

Although all three drugs are generally well tolerated, side effects, it is still possible.

The most common side effects:

• Viagra: facial flushing, headache, upset stomach
• Levitra: red face, headache
• Cialis: headache, upset stomach

Less common side effects:

• Viagra: altered vision, dizziness, nasal, congestion
• Levitra: heartburn, nausea, dizziness, stuffy nose
• Cialis: back pain, muscle aches, nasal congestion, facial flushing, dizziness

Precautions and contraindications

All PDE-5 inhibitors are absolutely contraindicated in individuals who take organic nitrates.

Alpha-blockers

• Viagra precautionary labeling advising against taking 50 mg or 100 mg dose four hours after administration of alpha-blockers. 25 mg of Viagra has not been shown to significantly reduce blood pressure in patients who take 25 mg of Viagra, the use of any of the alpha-blockers is considered safe.
• Levitra is contraindicated in patients taking alpha-blockers.
• Cialis is contraindicated in patients taking alpha-blockers, other than tamsulosin (Flomax).

As Viagra and Levitra have moderate vasodilatory and hypotensive effects, they should not be reduced in the presence of marked arterial or orthostatic hypotension and should be administered only with caution in aortic stenosis or hypertrophic obstructive cardiomyopathy.

Men who have had a heart attack or stroke within the last 6 months and those with certain diseases (eg, uncontrolled high blood pressure, severe low blood pressure or liver disease, unstable angina), making inappropriate sexual activity should not take Cialis. The dose should be limited to patients with kidney or liver disease.

Conclusions

Differences between the 3 drugs are not large. All appear to be an effective and safe. Levitra has fewer side effects compared to Viagra and lasts about the same time as Viagra in the body. Cialis has few side effects and lasts longer in the body. This allows a greater spontaneity and less than the dosage or Levitra or Viagra. Nevertheless, more than half life Cialis imposes an increased risk of drug interactions.