A case of priapism associated with paliperidone

To the Editor

This is a case of priapism occurring in a patient on paliperidone. Priapism occurs as a rare side effect described with most antipsychotic medications, although there have been no case reports with paliperidone to date (Paklet et al., 2013). Priapism is a painful, prolonged erection, which can have serious consequences such as impotency.

Priapism is thought to be mediated via the alpha-1 adrenergic antagonist effects of medications. Ziprasidone and risperidone have the highest affinity for the adrenergic receptors followed by clozapine and quetiapine. Paliperidone, like risperidone, has a relatively high affinity for adrenergic receptors (Sood et al., 2008). The absence of case reports associated with paliperidone is likely to relate to the fact that it is a relatively new drug and priapism is a rare side effect.

Mr A is a 38-year-old man with a diagnosis of schizophrenia from 20 years previously. He was assessed in 2012 because of an increase in auditory hallucinations and paranoid ideation. He described clear episodes of intense badgering by multiple external voices that left him disorientated and confused. His family also reported that paranoid ideation regarding neighbours had resulted in multiple house moves. He had been on trifluoperazine 5 mg for many years.

The hallucinations and paranoid ideation were both highly distressing to Mr A and his family. His antipsychotic was changed to paliperidone 6 mg and increased to 9 mg after 1 month, resulting in excellent resolution of symptoms with no significant side effects. Mr A had 12 months of significantly improved function.

In January 2014, Mr A experienced one episode of painless, prolonged erection that spontaneously resolved. This episode was followed 3 weeks later with an episode of priapism that was intensely painful and distressing. Mr A had no other risk factors for priapism. He presented to the emergency department of the local hospital. Conservative management failed and he underwent a Winter shunt followed by an Al-Ghorab shunt. He has been left with impotency.

He was commenced on olanzapine 10 mg due to its relative low affinity for adrenergic receptors, although case reports of priapism have been reported with this medication. Both aripiprazole and amisulpiride would be reasonable choices for treatment (Paklet et al., 2013).

Although priapism is a rare side effect it can be devastating for patients. Clinically it can be very difficult to consider rare side effects and how to approach discussion with our patients.