Related Experiment Video
Updated: Jun 11, 2026

Cellular Redox Profiling Using High-content Microscopy
Published on: May 14, 2017
Antipsychotic-induced priapism in an HIV patient: a cytochrome P450-mediated drug interaction
Background:
With upwards of 48% of human immunodeficiency virus (HIV)-infected persons having a probable psychiatric disorder, the possibility of cross-class drug interactions causing adverse effects or fatalities exists.
Aims:
This report discusses an emergent case of low-flow priapism caused by an interaction between a previously prescribed combination protease inhibitor (PI) and newly added antipsychotic medications.
Methods:
A 50-year-old HIV-positive man on highly active antiretroviral therapy (HAART), including the combination PI, lopinavir/ritonavir (Kaletra((R))), experienced an episode of priapism hours after beginning two new antipsychotic medications. Quetiapine (Seroquel((R))) and perphenazine (Trilafon((R))) were added to treat a diagnosed schizoaffective disorder.
Results:
The patient presented to the emergency department complaining of a constant, painful erection lasting approximately 42 h. Treatment with intracavernous ephedrine, irrigation, and aspiration helped achieve detumescence.
Conclusion:
This case displays the immediate and detrimental effects due to the addition of antipsychotic medications to previously altered cytochrome P450 (CYP450) enzyme levels. The inhibition of CYP450 enzymes 3A4 and 2D6 by the combination PI, lopinavir/ritonavir, was likely the major culprit in causing greater than expected free levels of perphenazine and quetiapine resulting in priapism.
Related Concept Videos
Effect of Hepatic Disease on Pharmacokinetics: Dose Adjustments Due to Hepatic Impairment
Pharmacokinetics: Drug–Drug Interactions
Treatment for Pulmonary Arterial Hypertension: Phosphodiesterase Inhibitors
Among the PDE5 inhibitors, sildenafil (Revatio) stands out as a competitive and selective inhibitor. It operates by elevating cellular levels of cGMP and augmenting signaling through the cGMP-PKG pathway, promoting vasodilation. Upon oral...
Pharmacokinetics: Drug–Food and Drug–Viral Interactions
Drug toxicity: Drug–Drug Interaction
Drug toxicity: Idiosyncratic Reactions

