Can anticholinergic medications cause priapism?

Anticholinergic Medications and Priapism

Anticholinergic medications are not commonly associated with priapism; instead, medications with alpha-adrenergic blocking properties are the primary pharmacological cause of priapism.

Medications That Commonly Cause Priapism

• Alpha-adrenergic antagonists are the primary pharmacological cause of priapism, with approximately 50% of drug-related priapism being attributed to antipsychotic usage 1
• The mechanism of priapism associated with these medications is related to alpha-adrenergic blockade that is mediated by the alpha receptors in the corpora cavernosa of the penis 2, 3
• Medications with strong alpha-adrenergic blocking properties that can cause priapism include:
  • Antipsychotics (both typical and atypical):
    • Chlorpromazine - has high alpha-1 adrenergic affinity and is frequently reported to cause priapism 4, 3
    • Thioridazine - has high alpha-1 adrenergic affinity 3
    • Risperidone, clozapine, quetiapine, olanzapine, ziprasidone, and aripiprazole have all been reported to cause priapism 2, 5
  • Antidepressants:
    • Trazodone - specifically mentioned in FDA labeling as causing priapism, even at doses as low as 100 mg 6, 7

Anticholinergic Medications and Priapism

• Pure anticholinergic medications (those that primarily block muscarinic receptors) are not specifically associated with priapism in the medical literature 8
• Many medications that have anticholinergic properties also have other pharmacological effects (particularly alpha-adrenergic blockade) that may contribute to priapism 3
• The American Urological Association guidelines on priapism do not list anticholinergic medications among the common causes of priapism 8

Risk Factors and Mechanism

• Priapism is considered an idiosyncratic reaction, as it is correlated neither with the dose nor duration of psychotropic drug use 5
• The best predictor for developing priapism is a past history of having prolonged erections 1
• Additional risk factors include:
  • Sickle cell disease or other hematologic abnormalities 8, 6
  • Anatomical deformation of the penis 6
  • Concurrent use of multiple medications with alpha-adrenergic blocking properties 2

Clinical Implications

• Priapism is a urological emergency that requires prompt evaluation and management 9
• If not treated promptly, priapism can result in irreversible damage to erectile tissue 6
• Men who have an erection lasting greater than 4 hours, whether painful or not, should immediately discontinue the causative drug and seek emergency medical attention 6
• Phenylephrine (an alpha-1 selective adrenergic agonist) is the recommended treatment for ischemic priapism 8

Prevention and Monitoring

• Clinicians should educate patients treated with medications that have alpha-adrenergic blocking properties about the potential for priapism 1
• When prescribing medications with known risk of priapism, caution should be used when adding new drugs to the regimen, and patients should be closely monitored 2
• In patients with recurrent (stuttering) priapism, preventive strategies may include hormonal agents or self-injection of phenylephrine 8

In summary, while anticholinergic medications themselves are not commonly associated with priapism, many medications that have anticholinergic properties also have alpha-adrenergic blocking effects that can cause priapism. The medications most commonly implicated are antipsychotics (particularly those with strong alpha-1 adrenergic antagonism) and trazodone.