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Higher than recommended doses of diarrhea drug loperamide (Imodium) can cause serious and even fatal cardiac arrhythmias, the FDA warned.
Although some of the 48 cases of QT interval prolongation, torsades de pointes, cardiac arrest, syncope, and other serious cardiac events reported to the agency have been unintentional misuse of more than the maximum daily dose for adults (8 mg in over-the-counter products; 16 mg in prescription use), most have been intentional abuse.
"The majority of reported serious heart problems occurred in individuals who were intentionally misusing and abusing high doses of loperamide in attempts to self-treat opioid withdrawal symptoms or to achieve a feeling of euphoria," the agency noted in a .
Loperamide is a mu-opioid agonist that acts primarily in the gut but, in high doses, has psychoactive effects. It has recently been and is recommended in internet chat forums for treating symptoms of opioid withdrawal.
Taking loperamide with , including ranitidine (Zantac), increases the risk. These combinations, too, are often intentional in "attempts to increase its absorption and penetration across the blood-brain barrier, inhibit loperamide metabolism, and enhance its euphoric effects."
The problem appears to have exploded in recent years. More than half of the 48 cases of serious heart problems reported to the FDA since the drug was approved in 1976 occurred in the short span from 2010 to 2015. Of those cases, 31 resulted in hospitalization and 10 in death. The most severe cases were among people taking four to 100 times the recommended loperamide dose.
"Consider loperamide as a possible cause of unexplained cardiac events including QT interval prolongation, torsades de pointes or other ventricular arrhythmias, syncope, and cardiac arrest," the FDA recommended to clinicians.
Standard toxicology and opioid drug screens don't include an assay for loperamide and will turn up a negative result in the presence of loperamide. If loperamide toxicity is suspected, blood levels should be measured by specifically requesting the test for the drug, the FDA suggested.
Antiarrhythmic drugs have been ineffective in many reported cases of loperamide-associated torsades de pointes, the agency added, so electrical pacing or cardioversion should be considered.
The FDA said it will continue to watch this safety issue to see if additional actions are needed.