Tadalafil – Long-Acting PDE5 Inhibitor for ED and BPH

Tadalafil is a reversible, selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE-5). The drug was developed for the pathogenic therapy of erectile dysfunction (ED), symptoms of benign prostatic hyperplasia (BPH), and pulmonary arterial hypertension (PAH). Its mechanism of action is based on the blockade of the PDE-5 enzyme, which prevents the hydrolysis of cGMP in vascular smooth muscle cells. This leads to the accumulation of cGMP, prolonged relaxation of smooth muscles, dilation of arterioles, and increased blood flow to the corpora cavernosa of the penis during sexual stimulation, as well as a decrease in pressure within the pulmonary vascular bed.

A unique pharmacokinetic feature of tadalafil that distinguishes it from other PDE-5 inhibitors (such as sildenafil or vardenafil) is its long half-life, which is approximately 17.5 hours. This provides an unprecedented duration of therapeutic effect — up to 36 hours after a single dose, earning the drug the unofficial nickname "the weekend pill." This prolonged window of efficacy allows patients to engage in sexual activity spontaneously without the need to plan ahead, thereby reducing psychological stress. The drug effectively improves pelvic organ perfusion, helping to ameliorate lower urinary tract symptoms associated with BPH. Tadalafil is rapidly absorbed after oral administration, and its bioavailability and onset of action are not affected by high-fat meals or alcohol consumption.

The drug is administered orally. To achieve a therapeutic effect for erectile dysfunction, the presence of natural sexual stimulation is an absolute prerequisite.

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Indications

Tadalafil is indicated for the treatment of adult patients with the following clinical conditions:

Erectile Dysfunction: therapy for erectile disturbances characterized by the inability to attain or maintain a penile erection sufficient for satisfactory sexual performance.
Benign Prostatic Hyperplasia (BPH): management of lower urinary tract symptoms in patients with prostate enlargement (either associated with ED or as monotherapy).
Pulmonary Hypertension (PAH): pathogenic treatment of WHO Functional Class I–IV pulmonary arterial hypertension to improve exercise capacity.

Dosage and administration

The dosing regimen of tadalafil depends on the indication, severity of the disease, and the chosen management strategy (on-demand or daily use).

For "on-demand" ED therapy: the recommended starting dose is 20 mg, taken at least 30 to 40 minutes prior to anticipated sexual activity.
For once-daily use (ED and/or BPH): the regular dose is 5 mg taken orally once daily at approximately the same time, regardless of the timing of sexual activity.
For Pulmonary Arterial Hypertension (PAH): the standard daily dose is 40 mg (two 20 mg tablets) taken once daily.
Administration Method: tablets are swallowed whole with water, with or without food. Splitting or chewing the tablets is not recommended.
Dose Adjustment: in patients with moderate renal or hepatic impairment, the maximum dose for on-demand use should not exceed 10 mg.

The use of tadalafil is strictly limited due to the risk of severe cardiovascular complications:

Hypersensitivity: known allergy or individual hypersensitivity to tadalafil or any of the tablet excipients.
Nitric Oxide Donors and Nitrates: absolutely contraindicated for concomitant use with any organic nitrates or medications that release nitric oxide (e.g., nitroglycerin, isosorbide dinitrate).
Cardiovascular Risks: myocardial infarction within the last 90 days, unstable angina, severe heart failure, uncontrolled arrhythmias, or hypotension (blood pressure less than 90/50 mmHg).
Stroke: history of an acute cerebrovascular accident (stroke) within the last 6 months.
Vision Loss: history of non-arteritic anterior ischemic optic neuropathy (NAION).

The side effects of tadalafil are typically transient and driven by the systemic vasodilatory effects of PDE-5 inhibitors:

Nervous System: headache (the most frequent symptom), occasional dizziness, and facial flushing with a sensation of heat.
Musculoskeletal System: myalgia (muscle pain) and pronounced back pain, caused by mild inhibition of PDE-11 in muscle tissue.
Digestive Tract: dyspepsia (indigestion), heartburn, gastroesophageal reflux, and nausea.
Respiratory System: nasal congestion, swelling of the nasopharyngeal mucosa, and rhinorrhea.
Sensory Organs: very rarely — blurred vision, altered color vision (cyanopsia), or sudden decrease or loss of hearing.

Frequently Asked Questions

Tadalafil is a selective, reversible inhibitor of phosphodiesterase type 5 (PDE5). By inhibiting this enzyme, the substance promotes the relaxation of vascular smooth muscle and increases blood flow to the pelvic organs. The defining characteristic of tadalafil is its prolonged half-life, which allows its therapeutic effect to persist for up to 36 hours after administration (unlike other drugs in this class, which remain effective for only 4 to 5 hours).

Tadalafil is indicated for several major medical conditions: the treatment of erectile dysfunction in men, the management of lower urinary tract symptoms in patients with benign prostatic hyperplasia (BPH), and, at specific distinct dosages, the treatment of pulmonary arterial hypertension to improve exercise capacity.

Co-administration of tadalafil with organic nitrates or nitric oxide donors (medications frequently used for angina and chest pain, such as nitroglycerin) results in a potent, synergistic enhancement of vasodilatory effects. This can precipitate a sudden, life-threatening drop in blood pressure (severe hypotension), collapse, or myocardial infarction.

The method of administration depends heavily on the therapeutic target. For the treatment of erectile dysfunction, the drug can be taken either "on demand" (at least 30 minutes prior to anticipated activity) or as a continuous daily regimen at a lower dose (e.g., 5 mg) taken at the same time each day. For BPH, only the continuous daily regimen is utilized. The tablets are taken orally, swallowed whole, and can be administered with or without food.

Common side effects include headache, indigestion (dyspepsia), facial flushing, nasal congestion, and back or muscle pain (myalgia). Urgent medical attention is required in rare, critical scenarios: if an erection lasts longer than 4 hours and is painful (risk of priapism), or if there is a sudden decrease or loss of vision or hearing.