1. Clinical Overview
Tadalafil is a potent, selective, and reversible inhibitor of phosphodiesterase type 5 (PDE5). The 5mg daily dose formulation is primarily indicated for the treatment of Benign Prostatic Hyperplasia (BPH) with or without Erectile Dysfunction (ED). It works by increasing blood flow to specific areas, leading to relaxation of smooth muscles in the prostate, bladder, and penis. In the Indian context, it is a widely prescribed and cost-effective option for chronic management.
| Onset | Duration | Bioavailability |
|---|---|---|
| 30 minutes to 6 hours (for on-demand dosing). For daily 5mg dose, therapeutic effect for BPH/ED is achieved after 4-5 days of continuous dosing. | Up to 36 hours (longest among PDE5 inhibitors). The 5mg daily regimen maintains a steady-state plasma concentration for continuous therapeutic effect. | Approximately 15-20%. |
2. Mechanism of Action
Tadalafil inhibits the enzyme phosphodiesterase type 5 (PDE5), which is responsible for the degradation of cyclic guanosine monophosphate (cGMP) in the corpus cavernosum of the penis, prostate, and bladder. Inhibition leads to increased intracellular cGMP levels. cGMP is a key mediator of nitric oxide (NO) signaling, causing smooth muscle relaxation and vasodilation.
3. Indications & Uses
- Benign Prostatic Hyperplasia (BPH) with lower urinary tract symptoms (LUTS)
- Erectile Dysfunction (ED)
- Concomitant BPH and ED
4. Dosage & Administration
Adult Dosage: For BPH or ED: 5mg once daily, taken at approximately the same time each day, without regard to food or sexual activity. For on-demand ED (not for 5mg tablet): 10mg at least 30 minutes before activity; may be increased to 20mg or decreased to 5mg based on tolerance.
Administration: Tablet to be swallowed whole with a glass of water. Can be taken with or without food. For the 5mg daily regimen, adherence to a fixed time is recommended for consistent effect. Do not crush or chew.
5. Side Effects
Common side effects may include:
- Headache
- Dyspepsia (indigestion)
- Back pain
- Myalgia (muscle ache)
- Nasopharyngitis (common cold symptoms)
- Flushing
- Nasal congestion
- Pain in extremity
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Nitrates (Nitroglycerin, Isosorbide) | Profound hypotension, potentially fatal. | Contraindicated |
| Alpha-blockers (Doxazosin, Tamsulosin, Prazosin) | Symptomatic hypotension (dizziness, lightheadedness). Tadalafil 5mg daily with alpha-blockers should be initiated only if patient is stable on alpha-blocker therapy. | Major |
| Potent CYP3A4 Inhibitors (Ketoconazole, Itraconazole, Ritonavir, Clarithromycin) | Significantly increases tadalafil exposure. For daily tadalafil, avoid concomitant use. For on-demand, max dose is 10mg every 72 hours. | Major |
| Antihypertensives | Additive hypotensive effect. | Moderate |
| Riociguat | Hypotensive synergy; contraindicated. | Contraindicated |
| Alcohol | Potentiates vasodilation and hypotensive effects, increases risk of dizziness and tachycardia. | Moderate |
7. Patient Counselling
- DO take the 5mg tablet once daily at the same time for BPH/ED, as prescribed.
- DO inform your doctor about all your current medications, especially nitrates (for chest pain), alpha-blockers (for BPH/BP), and antifungal/antiviral drugs.
- DO seek immediate medical attention if an erection lasts more than 4 hours.
- DO NOT take tadalafil if you are taking any form of nitrate medicine or riociguat.
- DO NOT take more than one dose in a 24-hour period unless directed by your doctor.
- DO NOT share your medication with others.
8. Toxicology & Storage
Overdose: Expected to be an extension of side effects: severe headache, flushing, dyspepsia, prolonged erection, dizziness, syncope, hypotension, tachycardia. In extreme cases, cardiovascular collapse.
Storage: Store below 30°C. Protect from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.