Dwagra 25

- Sildenafil a novel effective oral therapy for male erectile 
  dysfunction, is the citrate salt of Sildenafil, a selective 
  inhibitor of phosphodiestrase type 5 (PDE5), that enhances 
  the effect of  nitric oxide during sexual stimulation which 
  results in increased levels of cyclic guanosine  
  monophosphate producing smooth muscle relaxation in the 
  corpus cavernosum, allowing inflow of blood and hence 
  increasing the pressure in the penis and leading to 
  tumescence.  The erectile response generally increased with 
  increasing sildenafil dose and plasma concentration. The time 
  course of effect for up to 4 hours but the response may be 
  diminished compared to 2 hours. 
- Sildenafil at recommended doses has no effect in the absence  
  of  sexual stimulation. 
- The decrease in blood pressure was most notable  
  approximately 1- 2 hours after single oral dose of sildenafil, 
  this effect is not releated to dose or plasma levels. 
- Sildenafil is rapidly absorbed following administration by 
  mouth, with a bioavailability of approximately 40%. Peak 
  plasma concentrations are attained within 30 to 120 minutes; 
  the rate of absorption is reduced when administered with 
  food. It is widely distributed into tissues and is approximately 
  96% bound to plasma proteins.
-Sildenafil is metabolized in the liver primarily by cytochrome 
  P450 3A4 and  P450 2C9 isoforms. The major metabolite 
  N-desmethylsildenafil has the same activity of Sildenafil , 
  The major metabolite has a potency for PDE5 approximately 
  50% of the parent drug. 
- Excretion is predominantly as metabolites in the faeces and  
  to a lesser extent in the urine.