Correlation between blood magnesium and calcium concentration in patients treated with an anti-EGFR antibody

BACKGROUND: Hypomagnesemia is one of the characteristic side effects of the human anti-epidermal growth factor receptor (EGFR) monoclonal antibodies, cetuximab and panitumumab. The major mechanism of anti-EGFR antibody-related hypomagnesemia is suppression of EGFR-mediated urinary Mg(2+) reabsorption in both the renal tubule the intestinal tract. Since Mg(2+) is known to affect blood Ca(2+) levels through regulation of parathyroid hormone (PTH) secretion, we investigated the correlation between Ca(2+) and Mg(2+) concentration in blood. METHODS: Between April 2012 and October 2015, blood Mg(2+) and Ca(2+) concentrations (albumin corrected value) of 22 colon cancer patients undergoing treatment with either cetuximab or panitumumab at Toyooka Public Hospital were measured simultaneously. RESULTS: Hypomagnesemia (of all Grades) was reported in 13 of 22 patients. Two patients had hypomagnesemia of severity > Grade 3. Changes in blood Mg(2+) and Ca(2+) concentration showed a significant correlation (r(2) = 0.7455), which could be expressed using the following equation, Ca(2+) concentration = 1.4268 × (Mg(2+) concentration) + 7.1126. CONCLUSION: Since the early stages of hypomagnesemia produce no characteristic clinical symptoms, it is easily overlooked until it becomes severe. The investigation results suggest that if low blood Ca(2+) concentration (mg/dL) is observed in patients administered anti-EGFR antibodies, early evaluation of blood Mg(2+) concentration (mg/dL) and prompt supportive care are required to prevent aggravation of hypomagnesemia.