Induction of potentially lethal hypermagnesemia, ischemic colitis, and toxic megacolon by a preoperative mechanical bowel preparation: report of a case

A 67-year-old man was diagnosed with rectal cancer. The tumor invaded the subserosal layer, but it was not large, and there was no sign of obstruction. Neo-adjuvant chemotherapy reduced the size of the tumor. The patient was admitted to our hospital for surgery. For mechanical bowel preparation, he ingested 34 g of magnesium citrate (Magcorol P®), but then developed severe shock, a disturbance of consciousness, and acidemia, and he required catecholamines and mechanical ventilation. X-ray, CT, and laboratory tests revealed ischemic colitis, toxic megacolon, and hypermagnesemia (16.3 mg/dL). After 2 days of temporary hemodialysis and an enema to reduce his blood magnesium concentration, he recovered and left the intensive care unit. However, the left side of his colon had suffered ischemic damage and become irreversibly atrophied. One month later, he underwent laparoscopic abdominoperineal resection and left-side colectomy for the rectal cancer and severe ischemic colitis of the left side of the colon. Histopathology confirmed the rectal cancer with a grade 2 chemotherapeutic effect and severe ischemic colitis of the left side of the colon. Hence, the present case suggests that severe ischemic colitis, toxic megacolon, and hypermagnesemia can occur after taking a magnesium laxative without obstruction of the intestine.