What is the pharmacokinetic profile of tadalafil?

 Pharmacokinetics (PK) simply stated is ‘‘what  the body does to the drug’’ (ie, how the drug  is absorbed, eliminated and metabolized). Pharmacodynamics  or PD is ‘‘what the drug does to  the body.’’  Absorption: After single oral-dose administration  of tadalafil, the maximum observed  plasma concentration (Cmax) is achieved  between 30 minutes and 6 hours (median time  of 2 hours), although an erectogenic effect is  not predicated on the need to reach Cmax. The  time to reach Cmax is referred to as Tmax.  Neither the rate nor the extent of absorption of  tadalafil is influenced by food. Thus tadalafil  may be taken with or without food.  Metabolism: Tadalafil is predominantly metabolized  by CYP3A4 to a methyl catechol glucuronide  metabolite. In vitro data suggest  that metabolites are not expected to be pharmacologically  active following a dose of  tadalafil.  Elimination: The mean elimination half-life  (also sometimes referred to as ‘‘terminal halflife’’)  for tadalafil is 17.5 hours in healthy  subjects. The half-life is the time it takes for  the plasma concentration of drug in the body  to be reduced by 50%. Tadalafil is excreted  predominately as inactive metabolites, mainly  in the feces and to a lesser extent, urine. 
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