UC Davis

Introduction

Monensin is a veterinary antibiotic with a narrow therapeutic window that has led to lethal intoxication in many animal species. Only two prior cases of human toxicity have been reported, both fatal. We present the first case of survival from severe toxicity following monensin ingestion.

Case

A 58-year-old man presented with 8 days of vomiting and abdominal pain. Due to delusions of central nervous system toxoplasmosis, he ingested 300 mg of monensin. His laboratory studies revealed severe rhabdomyolysis without renal dysfunction. Total creatine kinase (CK) peaked above 100,000 U/L. His CK decreased to 5192 U/L after 15 days of aggressive hydration and sodium bicarbonate therapy. His ejection fraction on echocardiogram decreased from 69 to 56%.

Discussion

Reports on acute clinical effects after human exposure to monensin are limited. Ingestion is known to cause skeletal and cardiac muscle rhabdomyolysis and necrosis. Animal studies demonstrate that monensin's toxicity is due to increases in intracellular sodium concentrations and Ca²⁺ release. To date, no effective antidotal treatment has been described.

Conclusions

Monensin is a veterinary medication not approved for human use by the US Food and Drug Administration. Though poorly studied in humans, this case demonstrates the severe harm that may occur following ingestion.