Tadalafil works by inhibiting a specific enzyme, phosphodiesterase-5 (PDE5). This enzyme breaks down cyclic guanosine monophosphate (cGMP), a crucial molecule involved in the relaxation of smooth muscles.
Increased cGMP Levels
By blocking PDE5, tadalafil allows cGMP levels to rise. Elevated cGMP leads to increased blood flow, particularly in the penis, resulting in improved erectile function.
Impact on Blood Vessels
This increased blood flow is achieved through the relaxation of smooth muscles in the blood vessel walls. Consequently, the vessels dilate, accommodating a greater volume of blood.
Beyond Erectile Dysfunction
While predominantly known for treating erectile dysfunction, this mechanism also explains tadalafil’s use in treating pulmonary arterial hypertension (PAH). In PAH, constricted blood vessels in the lungs impede blood flow. Tadalafil’s PDE5 inhibition improves blood flow in the pulmonary arteries, alleviating symptoms.
Pharmacokinetic Considerations
| Half-life | 17.5 hours |
| Bioavailability | ~15% (oral), higher sublingually |
| Metabolism | Primarily hepatic |
Sublingual Administration
Sublingual administration offers faster absorption compared to oral ingestion, leading to a quicker onset of action. This route avoids first-pass metabolism in the liver, increasing bioavailability.
