Risk of Priapism with Daily 5 mg Tadalafil
Priapism with daily tadalafil 5 mg is exceedingly rare—clinical trials enrolling thousands of men with BPH did not report a single case of priapism, and postmarketing surveillance data indicate prolonged erection and priapism occur only infrequently with all PDE5 inhibitors. 1
Evidence from Clinical Trials
No cases of priapism were reported in randomized controlled trials evaluating PDE5 inhibitors (including tadalafil) for erectile dysfunction or BPH, despite enrollment of thousands of patients. 1
In long-term safety studies of tadalafil 5 mg once daily extending up to 2 years (N=472 patients), no study drug-related serious adverse events related to priapism or prolonged erection were observed. 2
A multicenter prospective study of 158 men receiving tadalafil 5 mg once daily for BPH (119 completed 12 weeks) reported zero cases of priapism, with the most common adverse effects being facial flushing (5.0%), headache (1.7%), and dizziness (1.7%). 3
Phase III trials specifically enrolling men with BPH treated with tadalafil 5 mg once daily for up to 1 year documented no priapism events, with adverse events limited to mild-to-moderate intensity effects such as dyspepsia, headache, and back pain. 4, 5
Postmarketing Surveillance Data
Prolonged erection and priapism were reported infrequently during postmarketing surveillance of all PDE5 inhibitors, but the absolute incidence remains extremely low and was not quantified in the guideline evidence. 1
The American College of Physicians guideline notes that serious adverse events with PDE5 inhibitors occurred in less than 2% of patients, with no difference between PDE5 inhibitors and placebo for serious events. 1
Clinical Context for Older Men with BPH
Older men being treated for BPH represent a lower-risk population for priapism compared to younger men using higher on-demand doses for erectile dysfunction, because the 5 mg daily dose produces steady-state plasma levels without the peak concentrations seen with 10–20 mg on-demand dosing. 4, 5
The most common adverse effects in BPH trials were headache, flushing, rhinitis, dyspepsia, back pain, and myalgia—none of which are related to priapism risk. 1, 4
Critical Caveat: Absolute Contraindication in Patients with Prior Priapism
If the patient has any history of prolonged priapism (>4 hours) while using any PDE5 inhibitor, tadalafil is absolutely contraindicated regardless of dose, because prior priapism indicates a predisposition to repeat episodes that can cause permanent erectile tissue damage, corporal fibrosis, and irreversible erectile dysfunction. 6
No "safe" dose of tadalafil exists for BPH in patients with previous PDE5-inhibitor-induced priapism; even the 5 mg daily formulation carries the same mechanistic risk of enhancing nitric-oxide-mediated vasodilation and smooth-muscle relaxation. 6
Tadalafil's long half-life (~17.5 hours) would prolong any priapism episode, making it more difficult to manage compared with shorter-acting agents. 6
Prescribing tadalafil to a patient with documented prior priapism falls below the standard of care and creates significant medicolegal liability, because recurrent priapism can lead to permanent erectile dysfunction and the need for penile prosthesis implantation. 6
Practical Recommendation
For older men with BPH and no history of priapism, daily tadalafil 5 mg carries negligible priapism risk and can be prescribed safely. 1, 2, 3, 4, 5 However, always screen for any prior history of prolonged erection or priapism with any PDE5 inhibitor before prescribing, because this represents an absolute contraindication. 6