1. Clinical Overview
Tadalafil is a potent, selective, and reversible inhibitor of phosphodiesterase type 5 (PDE5). The 2.5 mg strength is specifically indicated for the once-daily management of erectile dysfunction (ED) and for the treatment of benign prostatic hyperplasia (BPH) with or without ED. It is a long-acting agent that provides continuous therapeutic coverage, allowing for spontaneous sexual activity.
| Onset | Duration | Bioavailability |
|---|---|---|
| Approximately 30 minutes to 1 hour after oral administration. | Up to 36 hours, enabling a prolonged therapeutic window. | 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 and in vascular smooth muscle. Sexual stimulation leads to the release of nitric oxide (NO), which activates guanylate cyclase, increasing cGMP levels. cGMP causes smooth muscle relaxation and vasodilation, allowing increased blood flow into the penis, resulting in an erection. By inhibiting PDE5, tadalafil increases and sustains cGMP levels, enhancing the erectile response.
3. Indications & Uses
- Once-daily treatment of Erectile Dysfunction (ED).
- Treatment of the signs and symptoms of Benign Prostatic Hyperplasia (BPH).
- Once-daily treatment of ED and the signs and symptoms of BPH (co-administered diagnosis).
4. Dosage & Administration
Adult Dosage: For ED/BPH: 2.5 mg taken orally once daily, at approximately the same time each day, without regard to timing of sexual activity.
Administration: Swallow the tablet whole with a glass of water. Can be taken with or without food. Avoid consumption of grapefruit or grapefruit juice as it may increase plasma concentrations. The tablet can be taken at any time of the day but should be taken consistently.
5. Side Effects
Common side effects may include:
- Headache
- Dyspepsia (indigestion)
- Back pain
- Myalgia (muscle pain)
- Nasopharyngitis (common cold symptoms)
- Flushing
- Nasal congestion
- Pain in extremity
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Nitrates (e.g., Nitroglycerin) | Profound hypotension, potentially fatal. | Contraindicated |
| Riociguat | Hypotension. | Contraindicated |
| Alpha-blockers (e.g., Tamsulosin, Doxazosin) | Symptomatic hypotension (dizziness, lightheadedness). Tadalafil 2.5mg daily can be used with stable alpha-blocker therapy, but initiate with caution. | Major |
| Potent CYP3A4 Inhibitors (e.g., Ketoconazole, Itraconazole, Ritonavir, Clarithromycin) | Significantly increases tadalafil exposure. Maximum dose should be 2.5 mg once daily. | Major |
| Antihypertensives | Additive blood pressure lowering effect. | Moderate |
| Alcohol | Potential additive blood pressure lowering and increased heart rate. | Moderate |
7. Patient Counselling
- DO take one tablet (2.5 mg) at the same time each day as prescribed.
- DO NOT take more than one tablet in 24 hours.
- DO NOT take tadalafil if you are taking any medicines containing nitrates (for chest pain) or riociguat.
- DO seek immediate medical help for an erection lasting more than 4 hours (priapism).
- DO inform all your healthcare providers (including dentists) that you are taking tadalafil.
- DO NOT start or stop any other medication without consulting your doctor.
8. Toxicology & Storage
Overdose: Expected to be an extension of its vasodilatory properties: severe headache, flushing, dyspepsia, prolonged erection, dizziness, hypotension, syncope, and potentially cardiac events.
Storage: Store at room temperature (15°C to 30°C). Protect from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.