Cardiac effects of loperamide overdose
April 29, 2016, 5:59 pm
Not your regular high: cardiac dysrhythmias caused by loperamide. Wightman RS et al. Clin Toxicol 2016 Jun;54:454-458
Loperamide is an over-the-counter anti-diarrhea medication that is available without prescription under a variety of brand names including Imodium. In therapeutic doses, loperamide acts as a peripheral mu-opioid receptor agonist but doesn’t cross the blood-brain barrier (BBB). However, in massive overdose loperamide can enter the brain and cause central opioid toxicity, including altered mental status and respiratory.
Although previously loperamide was thought to have little abuse potential, recent reports indicates that it’s increasing being used to produce a recreational “high” or to self-treat opioid withdrawal. It is sometimes called the “poor man’s methadone.”
A little-known manifestation of loperamide toxicity is cardiac dysrhythmias. This case report describes a 48-year-old woman who had ingested up to 40 tablets 2-mg loperamide daily for several weeks to “get a high.” On presentation to hospital she was somnolent and had slurred speech but had stable vital signs. EKG showed markedly increased QRS (164 ms) and QT (582 ms) intervals and no p-waves. After admission to the intensive care unit, she had repeated runs of non-sustained ventricular tachycardia that did not require specific treatment.
A loperamide level was sent and came back at 210 ng/mL (therapeutic ~ 1.2 ng/mL.) The authors state that this is the highest level ever reported in a non-fatal loperamide overdose.
In their discussion, the authors note that loperamide blocks cardiac potassium channels, an effect that would explain the QT prolongation. The authors speculate that QRS widening seen in this case was caused by sodium channel blockade.
Ii would point out that the authors claim that in 2 previously reported cases of loperamide overdose the resulting dysrhythmias were resistant to lipid emulsion rescue therapy. I pulled the relevant papers, and upon review it was not at all clear that either the data reported by Marraffa et al nor by Enakpene et al were sufficient to support those claims.