Tadalafil is a potent, selective, and reversible inhibitor of phosphodiesterase type 5 (PDE5), an enzyme found predominantly in the corpus cavernosum of the penis, vascular smooth muscle, and pulmonary tissue. It is a first-line oral therapy for erectile dysfunction (ED) and is also approved for the treatment of benign prostatic hyperplasia (BPH) and pulmonary arterial hypertension (PAH). Its unique pharmacokinetic profile, characterized by a long half-life, allows for both on-demand and once-daily dosing regimens, offering significant flexibility to patients.
Adult: For ED (on-demand): 10mg or 20mg taken at least 30 minutes prior to anticipated sexual activity. Maximum dosing frequency is once per day. For ED (daily): 2.5mg or 5mg once daily without regard to timing of sexual activity. For BPH/ED+BPH: 5mg once daily at approximately the same time each day.
Note: Tablet should be swallowed whole with a glass of water. Can be taken with or without food. For on-demand use, plan sexual activity within the 36-hour window of efficacy. Do not take more than one dose in a 24-hour period.
Tadalafil inhibits the enzyme phosphodiesterase type 5 (PDE5), which is responsible for the degradation of cyclic guanosine monophosphate (cGMP) in the corpus cavernosum. Sexual stimulation leads to the release of nitric oxide (NO), which activates guanylate cyclase, increasing cGMP levels. cGMP causes smooth muscle relaxation in the corpus cavernosum and penile arteries, allowing increased blood flow and erection. By inhibiting PDE5, tadalafil prevents the breakdown of cGMP, thereby potentiating the erectile response.
Pregnancy: US FDA Pregnancy Category B. Not indicated for use in women. No adequate and well-controlled studies in pregnant women. Animal studies have shown no direct harm to the fetus. However, it is not prescribed to women.
Driving: Due to potential side effects like dizziness, hypotension, and visual disturbances, patients should be cautious when driving or operating machinery, especially after the first dose or dose increase.
| Nitrates (e.g., Nitroglycerin, Isosorbide) | Profound, life-threatening hypotension | Contraindicated |
| Alpha-blockers (e.g., Tamsulosin, Doxazosin) | Symptomatic hypotension (dizziness, lightheadedness). Tadalafil dose should not exceed 5mg daily when co-administered with alpha-blockers. | Major |
| Potent CYP3A4 Inhibitors (e.g., Ketoconazole, Itraconazole, Ritonavir, Clarithromycin) | Significantly increases tadalafil exposure. Maximum dose: 10mg every 72 hours for on-demand; avoid daily dosing. | Major |
| Antihypertensives | Additive blood pressure lowering effect | Moderate |
| Riociguat | Hypotensive synergy; contraindicated | Contraindicated |
| Alcohol | Potentiation of orthostatic hypotension and dizziness | Moderate |