Comparison Of Sexual Dysfunction Medications

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

In around 95% of the cases, a suitable treatment can be found. Erectile dysfunction is treatable at any age, and awareness of this fact has been growing. More men have been 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 medications approved by the Food and Drug Administration (FDA) for the 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 is probably the most famous of the three PDE-5 inhibitors used to treat erectile dysfunction. Viagra was approved as an effective agent for treating erectile dysfunction in March 27, 1998. Viagra is manufactured by 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 manufactured by Bayer Pharmaceuticals Corporation.

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 is manufactured by Lilly ICOS LLC.

The major advantage of PDE-5 inhibitors is that they do not cause an erection 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 in the penis in response to sexual stimulation. However, there are important differences between the three, differences that could influence safety, specificity, duration of action, adverse effects, and ultimately, public acceptance within this class of drug.

Mechanism of Action

PDE-5 inhibitors do not directly cause an erection of the penis, but they 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.

Effectiveness of PDE-5 Inhibitors

All 3 PDE-5 inhibitors have demonstrated excellent efficacy. Viagra, at 84%, is slightly more effective than Cialis at 81% and Levitra at 80%.

Pharmaceutical Forms, Onset of Action and Duration of Effect

Viagra and Levitra differ only minimally in terms of their structure, while Cialis differs markedly from Viagra and Levitra in terms of its 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: 4 to 5 hours

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

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

Cialis: 5 mg, 10 mg, 20 mg tablets

• Onset of action: 16-45 minutes (effect 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 it works better if you do not eat a high-fat meal around the time you take it. Levitra may be slightly less effective if you eat a high-fat meal, but a moderate-fat meal does not reduce its effectiveness. Cialis works without regard to what you eat. Viagra and Levitra have similar half-lives, and onset and duration of action. Cialis has a slower onset of action and longer duration of action, which is attributed to its longer half-life.

Patients who wish for spontaneity may opt for Cialis, which may allow for successful intercourse up to 36 hours postdose, even though it takes longer to reach peak effect. The considerably longer duration of effect for Cialis will likely allow less frequent dosing and greater impulsiveness between partners, but also could potentially prolong adverse 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. A lower dose of 5 mg is available for patients who take other medicines or have conditions that may decrease the body's ability to use the drug. Levitra is also available in a 2.5 mg dose. 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 are still possible.

Most common side effects:

• Viagra: facial flushing, headache, indigestion
• Levitra: facial flushing, headache
• Cialis: headache, indigestion

Less Common Side Effects:

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

Precautions and Contraindications

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

Alpha-blockers

• Viagra has precautionary labeling advising against taking 50 mg or 100 mg doses within four hours of taking a alpha-blocker. The 25 mg dose of Viagra has not been shown to significantly decrease blood pressure and in patients who take 25 mg of Viagra, 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, except for tamsulosin (Flomax).

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

Men who have had a heart attack or stroke within the past 6 months and those with certain medical conditions (e.g., uncontrolled high blood pressure, severe low blood pressure or liver disease, unstable angina) that make sexual activity inadvisable should not take Cialis. Dosages of the drug should be limited in patients with kidney or liver disorders.

Conclusions

The differences between the 3 drugs are not great. All appear to be effective and safe. Levitra has less 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 increased spontaneity and less frequent dosing than either Levitra or Viagra. However, the longer half-life of Cialis imposes increased risk for drug interactions.