Chlorpromazine-tadalafil interaction leading to refractory ischemic priapism and penile prosthesis implantation: a case report

TL;DR

This case report describes a 56-year-old man who developed refractory ischemic priapism after self-administering chlorpromazine 25 mg for hiccups about 24 h after taking tadalafil 20 mg, with a prior chlorpromazine-associated transient priapism episode 10 years earlier. Despite aspiration, intracavernosal epinephrine, and distal T-shunt, priapism recurred and he underwent three-piece inflatable penile prosthesis implantation, with satisfactory 3-month outcomes.

Key findings

• The patient presented with a 72-h painful erection; corporal blood gas analysis showed pH 6.9, pO2 28 mmHg, and pCO2 60 mmHg, confirming ischemic priapism; toxicology screening and hemoglobin electrophoresis were negative.
• Chlorpromazine was identified as the primary etiological agent based on a prior approximately 4-h transient priapism episode after chlorpromazine alone 10 years earlier and positive rechallenge; tadalafil co-administration likely exacerbated the condition through synergistic alpha-1 adrenergic blockade and PDE-5 inhibition. The Naranjo Adverse Drug Reaction Probability Scale score was 9 points (definite adverse drug reaction).
• First-line corporal aspiration and intracavernosal epinephrine (1:100,000, then 1:50,000) failed; a distal T-shunt initially achieved detumescence, but priapism recurred approximately 6 h later. A three-piece inflatable penile prosthesis was implanted, the patient was discharged on postoperative day 2, and at 3 months he reported satisfactory function with no mechanical issues or pain.
• The authors recommend avoiding concurrent chlorpromazine and PDE-5 inhibitor use, considering safer hiccup alternatives such as baclofen 10 mg three times daily or metoclopramide 10 mg three times daily, and reporting such cases to pharmacovigilance systems.

Methods

• Design: single case report of a 56-year-old male with refractory ischemic priapism after chlorpromazine and tadalafil exposure; no control group or statistical analysis.
• Data: clinical history, physical examination, laboratory tests (complete blood count, coagulation profile, renal and liver function tests, hemoglobin electrophoresis), comprehensive toxicological screening, corporal blood gas analysis, treatment course, and 3-month follow-up.
• Main analysis: descriptive case synthesis with causality assessment using the Naranjo Adverse Drug Reaction Probability Scale (score 9, definite) and comparison with guideline-based stepwise management.

Limitations

• Stated: single-case design limits generalizability; no serum chlorpromazine or tadalafil concentrations were measured; CYP3A4 genetic polymorphisms were not assessed; self-medication dosing and timing rely on patient recollection; follow-up was limited to 3 months; alternative management strategies were not explored.
• Evident: there was no controlled comparison or pharmacokinetic confirmation, so the proposed synergistic interaction remains inferential despite the Naranjo score; the report cannot establish incidence or risk magnitude in broader populations.