Tadalafil
Tadalafil is a phosphodiesterase 5 inhibitor used to treat erectile dysfunction, benign prostatic hyperplasia, and pulmonary arterial hypertension.
Tadalafil is an orally administered drug used to treat male erectile dysfunction (impotence). It is marketed worldwide under the brand name Cialis. It is a phosphodiesterase 5 (PDE5) inhibitor. Tadalafil's distinguishing pharmacologic feature is its longer half-life (17.5 hours) compared with Viagra and Levitra (4-5 hours). This longer half-life results in a longer duration of action and is, in part, responsible for the Cialis nickname of the "weekend pill."
Type Small Molecule Groups Approved, Investigational Structure
Structure for Tadalafil (DB00820)
- (6R-trans)-6-(1,3-Benzodioxol-5-yl)-2,3,6,7,12,12a-hexahydro-2-methyl-pyrazino(1',2':1,6)pyrido(3,4-b)indole-1,4-dione
- (6R,12aR)-2,3,6,7,12,12a-Hexahydro-2-methyl-6-(3,4-(methylenedioxy)phenyl) pyrazino(1',2':1,6)pyrido(3,4-b)indole-1,4-dione
- Tadalafil
- Tadalafilo
- GF 196960
- IC-351
- IC351
- ICOS 351
Pharmacology
Used for the treatment of erectile dysfunction. It is also used in the treatment of pulmonary arterial hypertension.
Tadalafil is used to treat male erectile dysfunction (impotence) and pulmonary arterial hypertension (PAH). Part of the physiological process of erection involves the release of nitric oxide (NO) in the corpus cavernosum. This then activates the enzyme guanylate cyclase which results in increased levels of cyclic guanosine monophosphate (cGMP), leading to smooth muscle relaxation in the corpus cavernosum, resulting in increased inflow of blood and an erection. Tadalafil is a potent and selective inhibitor of cGMP specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernosum. This means that, with tadalafil on board, normal sexual stimulation leads to increased levels of cGMP in the corpus cavernosum which leads to better erections. Without sexual stimulation and no activation of the NO/cGMP system, tadalafil should not cause an erection.
Mechanism of action
Penile erection during sexual stimulation is achieved by the relaxation of penile arteries and corpus cavernosal smooth muscles, leading to increased blood flow to the organ. This response is mediated by the release of nitric oxide (NO) from nerve terminals and endothelial cells, which stimulates the synthesis of cGMP in smooth muscle cells. Cyclic GMP causes smooth muscle relaxation and increased blood flow into the corpus cavernosum, and is degraded by the cGMP specific phosphodiesterase type 5 (PDE5) in the corpus cavernosum located around the penis. Tadalafil inhibits PDE5 and thereby enhances erectile function by increasing the amount of cGMP available.
After single oral-dose administration, the maximum observed plasma concentration (Cmax) of tadalafil is achieved between 30 minutes and 6 hours (median time of 2 hours). Absolute bioavailability of tadalafil following oral dosing has not been determined.
- 63 L
Tadalafil is predominantly metabolized by CYP3A4 to a catechol metabolite. The catechol metabolite undergoes extensive methylation and glucuronidation to form the methylcatechol and methylcatechol glucuronide conjugate, respectively. In vitro data suggests the metabolites are not expected to be pharmacologically active at observed metabolite concentrations.
Route of elimination
Tadalafil is excreted predominantly as metabolites, mainly in the feces (approximately 61% of the dose) and to a lesser extent in the urine (approximately 36% of the dose).
