Viagra (Sildenafil Citrate) Reviews and Drug Information

Oral Phosphodiesterase

1. Inhibitors PDE­5
2. Pharmacokinetics and pharmacodynamics
3. Side effects
4. Safety
5. Comparison

Phosphodiesterase, as mentioned in the previous  section, is paramount to the breakdown of cGMP  in the SMC. This enzyme is found in several dif­ ferent tissues throughout the body and has been  categorized into 11 families. The family that is  found in corpora cavernosum tissue as well as  smooth muscle and vascular smooth muscle is  PDE­5. As the role of PDE­5 was elucidated in  the 1980s, drugs were targeted to inhibit this  enzyme and increase the NO in SMCs. A result  of this was an unexpected increase in NO in  penile tissue and improvement in erectile  function. PDE­5 inhibitors were first marketed in 1998  with the dawn of sildenafil (Viagra®). This was  followed closely in 2003 with vardenafil  (Levitra®) and tadalafil (Cialis®). As the market  for these drugs has increased, it has been impor­ tant to identify the safety, efficacy, and limita­ tions of these drugs. When choosing a PDE­5  inhibitor for a patient, it is important to know  the onset of action, efficacy, and duration.  Studies usually will define the maximal plasma  concentration (Cmax ), time to reach this plasma  concentration (Tmax ), and the plasma half­life  (t ½). How well these laboratory findings corre­ late to clinical findings is sometimes difficult to  determine and the measuring tool most com­ monly used to evaluate efficacy is the International Index of Erectile Function (IIEF)  domain score.

Viagra®

The most studied of these drugs is sildenafil  (Viagra®). In several placebo controlled, ran­ domized trials, this drug has been shown to  improve erectile function. The pivotal study for  sildenafil was published in 1998, which showed  a clinically and statistically significant improve­ ment in IIEF domain scores for men suffering  from ED for greater than 5 years. The onset  of action of sildenafil is approximately 20 min with a reported  t ½ of 3–5  h and duration of  action as long as 12 h. The important thing  about sildenafil is that it should not be taken  with a high­fat meal because this will decrease  the absorption of the medication. Female Viagra Australia

Levitra®

The FDA approved vardenafil (Levitra®) in  2003 after a study of 805 men with ED showed  a clinically and statistically significant improve­ ment in IIEF scores when compared to placebo. In this study, different doses were evaluated and  men were categorized into mild, moderate, and  severe ED. Approximately 40% of the moder­ ate and severe ED men had improvement with  the highest dose and over 79% of the mild ED  men had improvement. Vardenafil is  quickly absorbed with a Tmax  of 45 min and a  reported t ½ of 4–5 h. Onset of action has been  recorded as early as 10  min [17]. Just as in  sildenafil, it is recommended that high­fat meals  are avoided.