Tadalafil

Tadalafil is a medication used to treat erectile dysfunction, benign prostatic hyperplasia, and pulmonary arterial hypertension. It is taken by mouth. Onset is typically within half an hour and the duration is up to 36 hours.

Tadalafil was approved for medical use in the United States in 2003. It is available as a generic medication. In 2020, it was the 261st most commonly prescribed medication in the United States, with more than 1 million prescriptions.

Structure:

Physicochemical Data:

IUPAC Name     (6R,12aR)-6-(1,3-benzodioxol-5-yl)-2-methyl-2,3,6,7,12,12a-hexahydropyrazino[1′,2′:1,6]
pyrido[3,4-b]indole-1,4-dione
CAS Number171596-29-5
Molecular FormulaC22H19N3O4
Molecular Mass389.411 g·mol−1
Melting Point301-303°C
Density 

Pharmacokinetic Data:

AbsorptionTadalafil has a tmax of 0.5-6h with a median of 2h in healthy adults. The Tmax in adults with PAH is reported as 2-8h with a median of 4h. There does not appear to be a significant effect on absorption when tadalafil is taken with food.
Volume of DistributionTadalafil has a mean apparent volume of distribution of 63L in healthy adults. The mean apparent volume of distribution is reported as 77L in adults with PAH.
Protein BindingTadalafil is 94% bound to plasma proteins.
MetabolismTadalafil undergoes hepatic metabolism via CYP3A4 to a catechol metabolite. This catechol metabolite undergoes subsequent methylation and glucuronidation with the methyl-glucuronide metabolite becoming the primary metabolite in circulation. None of the known metabolites are considered to be active.
Route of EliminationTadalafil is primarily eliminated via hepatic metabolism. These metabolites are mainly excreted in the feces (61%) and to a lesser extent in the urine (36%).
Half-lifeThe mean half-life of elimination of tadalafil is 15-17.5h in healthy adults. The mean half-life of elimination in adults with PAH is reported as 35h.
ClearanceThe mean apparent oral clearance of tadalafil is 2.5-3.4L/h in healthy adults. The mean apparent oral clearance in adults with PAH is reported as 3.5L/h.
ToxicitySymptoms of overdose are expected to be similar to typical adverse effects which may include headache, dyspepsia, back pain, myalgia, nasopharyngitis, and dizziness. Standard supportive care is recommended. Hemodialysis is not expected to contribute significantly to tadalafil clearance.

References:

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