Published: 5 September 2014

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The Hard Facts on Drug-induced Priapism (Long-lasting Erections)

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Prescriber Update 35(3): 35
September 2014

What is priapism?

Priapism is a persistent, often painful, penile erection lasting more than four hours that is not associated with sexual interest or stimulation¹. It can occur in males of any age and occurs when blood in the penis becomes trapped.

At least 95% of all cases of priapism occur by an ischaemic (low-flow or veno-occlusive) mechanism. Ischaemic priapism is a type of compartment syndrome where pressure within the corpora cavernosa severely compromises circulation in the cavernous tissues¹.

What are the causes of priapism?

In the majority of cases, priapism is considered to be idiopathic¹.

The known causes or conditions associated with priapism include¹:

• medicines (see Table 1 below)
• haematological disorders (eg, sickle cell disease, leukaemia)
• metabolic disorders (eg, amyloidosis, gout)
• recreational drugs (eg, alcohol, cannabis, cocaine).

What medicines can cause priapism?

Drug-induced priapism can occur with a range of medicines; antipsychotics are the most common cause².

Table 1: Medicines associated with priapism

Medicine class	Examples
Medicines recognised as increasing the risk of priapism (adapted from Salonia et al)
Antipsychotics & Antidepressants	risperidone, olanzapine, clozapine, chlorpromazine, quetiapine, sertraline, citalopram, escitalopram, lithium, fluoxetine, trifluoperazine, pericyazine
Vasoactive erectile agents	alprostadil, papaverine
α-adrenergic receptor antagonists	doxazosin, tamsulosin, terazosin, prazosin
Antihypertensives	hydralazine, propranolol
Anticoagulants	heparin, warfarin
Hormones	testosterone, gonadotropin-releasing hormone
Medicines that have been reported to cause priapism 3, 4.
Phosphodiesterase type 5 inhibitors	sildenafil, tadalafil
Medicines used for ADHD	methylphenidate, atomoxetine

Are there other medicines that have been reported to cause priapism?

There have only been a few reported cases of priapism with the use of phosphodiesterase type 5 inhibitors, used to treat erectile dysfunction³.

Priapism has also been associated with methylphenidate treatment, both with dose increases and decreases⁴. The Medicines Adverse Reactions Committee recently considered this association and noted the possibility of more than one biological mechanism. This may be demonstrated by reports of priapism associated with both increase in dose and methylphenidate withdrawal.

The MARC also noted that whilst priapism appears to be a very rare reaction, it is likely to be under-reported and can have serious sequelae if treatment is not sought early enough.

Reports of priapism in New Zealand

The Centre for Adverse Reactions Monitoring (CARM) has received isolated reports of drug-induced priapism, including four reports with chlorpromazine and three reports with citalopram.

Internationally, there have been published case reports of priapism associated with medicines such as risperidone, quetiapine, sildenafil and olanzapine.

What information or advice about priapism should be given to patients?

Although priapism appears to be a very rare reaction, all male patients who are prescribed medicines that may cause priapism should be advised of the signs and symptoms.

Priapism or any erection lasting longer than four hours with or without sexual stimulation requires immediate medical attention to prevent long-term complications.

References:

1. Salonia A, Eardley I, Giuliano F, et al. 2014. European Association of Urology Guidelines on Priapism. European Urology 65: 480-489.
2. Thompson JW, Ware MR, Blashfield RK. 1990. Psychotropic medication and priapism: a comprehensive review. Journal of Clinical Psychology 51(10): 430-433.
3. Broderick GA, Kadioglu A, Bivalacqua TJ, et al. 2010. Priapism: Pathogenesis, epidemiology, and management. The Journal of Sexual Medicine 7: 476-500.
4. Food and Drug Administration. 2013. FDA warns of rare risk of long-lasting erections in males taking methylphenidate ADHD medications and has approved label changes. Drug Safety Communication 17 December 2013. URL: www.fda.gov/Drugs/DrugSafety/ucm375796.htm (accessed 16 July 2014).