Before the introduction of tadalafil (Cialis), other oral agents were available for the treatment of erectile dysfunction. In March 1998, with much ballyhoo, Viagra (sildenafil citrate) was released by Pfizer as the first oral agent approved by the FDA for the treatment of erectile dysfunction. In 2003, Levitra (vardenafil), the second oral agent, was released jointly by Glaxo Smith Kline and Bayer for treating ED.
The mechanisms of action for these agents are both very similar with regards to inhibiting phosphodiesterase 5. When this occurs with sexual stimulation, the relaxation of the smooth muscle of the penis is maximized, resulting in an erection. Both of these agents should not be used by patients who are using nitrate containing drugs due to the risk of developing profound hypotension.
Sildenafil needs to be used one hour prior to sexual activity. Ideally fatty foods should be avoided as the drug is not as effectively absorbed after the ingestion of high fat meals. The half life of the drug is limited (3-5 hours), thereby limiting the duration of the improvement in erectile response that may be seen with other agents.
The response rate of the drug is fairly reliable, and it is the oral agent that is supported by the largest body of clinical experience. The drug is available in 50 and 100mg doses but the minimal dose should first be attempted. Most patients with multiple underlying risk factors for erectile dysfunction tend to benefit from the larger dosage.
Vardenafil (Levitra) is also effected by fatty meals. Blood serum levels of the drug are significantly decreased with the ingestion of high fat meals. The drug should ideally be used 1 hour prior to sexual activity. The half life for this drug is similar to sildenafil at 4.5 hours.
These drugs are both metabolized in the liver, and special dosing considerations should be undertaken by patients who have underlying liver disease, or by those patients who are using drugs that are P-450 inhibitors. Some of these drugs include erythromycin, ketoconazole, erythromycin, ritonavir or indinavir. Side effects of these agents include headache, facial flushing, and visual changes.
Published On: November 22, 2006