What Happens to Sildenafil, Tadalafil and Vardenafil Inside the Body

Brand	Formulations	FDA Approval
Viagra	25mg, 50mg, 100 mg tablets	March 27, 1998
Cialis	5mg, 10mg, 20mg tablets in bottles of 30.	November 21, 2003
Levitra	2.5mg, 5mg, 10mg, 20mg tablets in bottles of 30.	August 19, 2003

A lot of attention has been given to what PDE5 inhibitors do to the human body, but now lets have a brief look at  how the the drugs – Viagra, Cialis and Levitra themselves change once they are introduced in the body. This article is not meant as an in depth reference, but aims to give a very basic outlook of the parameters involved.

Pharmacokinetics

Drug	Protein Binding	Bioavailability	Metabolism	Half Life	Excretion
Viagra	95%	41%	Active Metabolite CYP3A4 and 2C9	4 hours	81% fecal and 12% renal
Cialis	Not determined	Not determined	Inactive Metabolite CYP3A4	18 hours	62% fecal and 37% renal
Levitra	95%	16%	Active Metabolite CYP3A4	4 hours	90-%-96% fecal and 1-6% renal

Pharmacokinetics is the study of how the body changes the drug and what happens to it inside the human body. If you notice – the half life of Cialis is much higher than Viagra or Levitra- this translates to higher active window, remember it works for upto 36 hours. Again the increased half life means slower onset of action meaning it takes longer than Viagra and Levitra to work but stays in the body for longer.

Pharmacodynamics

Drug	Food Effect	Median Action Time	Action Duration
Viagra	Fatty food decreases action time and peak concentration levels.	28 minutes	4 hours
Cialis	Fatty food has negligible effect.	45 minutes	36 hours
Levitra	Fatty food decreases peak concentration levels.	27 minutes	4 hours

The above statistic is interesting. What it tells us is that the effect of Cialis is unaffected with fatty food whereas Viagra and Levitra show decreased action time and concentration levels when a man eats fatty food.