COMMON INITIAL DOSING REGIMENS

• For Erectile Dysfunction: An initial dose of 10 mg taken orally before anticipated sexual activity is common, with a maximum frequency of once per day. For daily use, a lower dose of 2.5–5 mg is recommended, irrespective of timing of sexual activity.

MECHANISM OF ACTION

• Tadalafil is a selective phosphodiesterase type 5 (PDE5) inhibitor. By inhibiting PDE5, tadalafil prevents the breakdown of cyclic guanosine monophosphate (cGMP) in the smooth muscle cells of the corpus cavernosum, pulmonary vasculature, and other vascular tissues.

• In ED, increased cGMP levels result in enhanced smooth muscle relaxation and increased blood flow to the penis during sexual stimulation, promoting erection.

• Tadalafil is distinguished by its long half-life (17.5 hours), which provides a prolonged duration of action, often referred to as the “weekend pill.”

COMMON SIDE EFFECTS

• Cardiovascular: Headache, flushing, and dizziness are common due to systemic vasodilation. Hypotension and tachycardia may occur but are less common.

• Gastrointestinal: Dyspepsia, nausea, and abdominal pain.

• Musculoskeletal: Back pain and myalgia are unique side effects of tadalafil, possibly related to PDE11 inhibition.

• Respiratory: Nasal congestion.

• Rare but Severe: Non-arteritic anterior ischemic optic neuropathy (NAION), sudden hearing loss, and priapism (prolonged erection requiring medical attention).

CONTRAINDICATIONS

• Absolute: Hypersensitivity to finasteride or any excipient in the formulation. Pregnant or potentially pregnant women should not handle finasteride-containing products due to the risk of absorption and potential harm to a male fetus.

• Relative: Patients with significant scalp irritation or broken skin should use topical finasteride cautiously to avoid increased systemic absorption. Use in women for androgenetic alopecia remains off-label and requires careful consideration.

ADDITIONAL NOTES ON EFFICACY

• Absolute: Concurrent use with nitrates (e.g., nitroglycerin) or guanylate cyclase stimulators (e.g., riociguat) due to the risk of severe hypotension. Hypersensitivity to tadalafil or any excipient.

• Relative: Use cautiously in individuals with severe hepatic or renal impairment, severe cardiovascular conditions, significant hypotension (<90/50 mmHg), or a recent history of stroke or myocardial infarction. Patients with retinitis pigmentosa or predisposing conditions for priapism (e.g., sickle cell anemia, multiple myeloma, leukemia) require additional caution.

COMPARISON WITH SILDENAFIL

• Tadalafil has a longer half-life (17.5 hours) compared to sildenafil (4–6 hours), allowing for greater flexibility with dosing and a prolonged therapeutic window. This makes tadalafil suitable for daily dosing and sustained effects (“weekend pill”).

• Tadalafil also has unique efficacy in managing BPH, which sildenafil does not address. Both medications share similar side effects, but tadalafil has a distinct risk of musculoskeletal pain.

MORE INFORMATION

• FDA Safety Data Sheet for tadalafil may be found here.