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Pharmacology: Pharmacodynamics: Tadalafil is a selective phosphodiesterase 5 (PDE5) inhibitor. PDE5 regulates nitric oxide-mediated vasodilatation through degradation of the second messenger cGMP and is abundantly expressed in lung tissue. Nitric oxide treatment involves the continuous insulation of nitric oxide to widen blood vessels in the lungs. It is given by mouth as the citrate although doses are expressed in terms of the base.
Pharmacokinetics: Tadalafil is well absorbed after dose by mount. Peak plasma concentrations are attained within 2 hours; the rate and extent of absorption are not affected by food. Tadalafil is widely distributed into tissues and is about 94% bound to plasma proteins. It is metabolized in the liver mainly by the cytochrome P450 isoenzyme CYP3A4. The mean half-life of Tadalafil is about 17.5 hours. Tadalafil is excreted, mainly as metabolites, in the feces (61% of the dose), and to a lesser extent urine (36% of the dose). Clearance may be reduced in the elderly and in patients with renal impairment.
