Panitumumab-related hypomagnesemia in patients with colorectal cancer

Purpose: Hypomagnesemia is an adverse reaction associated with epidermal growth factor receptor (EGFR)-targeting monoclonal antibodies. Of the 2 EGFR antibodies approved by the US Food and Drug Administration-cetuximab and panitumumab-cetuximab-induced hypomagnesemia has been extensively characterized but panitumumab-induced hypomagnesemia has not. Methods: In this retrospective study, the clinical course of hypomagnesemia is described in three 64- to 68-year-old men who received panitumumab monotherapy or panitumumab-plus- irinotecan therapy for colorectal cancer for 8 to 21 weeks. Results: The onset of hypomagnesemia was variable, ranging from 1 week to 10 weeks following the initiation of panitumumab. Magnesium levels did not normalize until 4 to 8 weeks after discontinuation of the agent. Of the patients in the study, 2 had new onset of grade 3 hypomagnesemia 1 to 3 weeks after panitumumab was discontinued. Management was magnesium sulfate 2 g infusion weekly and magnesium oxide 1,200 mg oral repletion daily. With severe hypomagnesemia (grade 3 and higher) or significant diarrhea (grade 3 and higher), a daily infusion of magnesium sulfate 2 or 4 g was administered. Conclusion: When administering panitumumab therapy, magnesium levels should be monitored from the initiation of the agent to at least 8 weeks following cessation. Hypomagnesemia usually can be managed with magnesium sulfate 2 to 4 g infusion weekly and magnesium oxide 1,200 mg oral repletion daily. Future research is warranted to identify simple and efficient strategies for monitoring and treating EGFR blockade with monoclonal antibody-associated hypomagnesemia.