Sunday, January 8, 2012

Tadalafil has a Tmax of 2 hours. Does this mean it takes 2 hours for tadalafil to work in men with ED?


No. Tmax is the time to peak plasma concentration  and is a pharmacokinetic property of the  drug. In contrast, time to onset of action is a  pharamcodynamic measurement assessed clinically  (i.e., the elapsed time between taking a  pill and achieving the desired clinical effect –  in this case, an erection). Because Tmax predicts  the time to maximum plasma concentration,  clinicians sometimes mistakenly equate  it with the time to onset of efficacy. However,  maximum plasma concentrations are typically  not required for efficacy. Consequently, the  time required to reach efficacious plasma  levels is usually shorter than the time required  to achieve peak plasma levels. 

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