© 2005 Oxford University Press
CORRESPONDENCE |
Re: Cetuximab Therapy and Symptomatic Hypomagnesemia
Affiliations of authors: Department of Medical Oncology, Institute of Oncology (KA), Department of Internal Medicine, Faculty of Medicine (ST), Hacettepe University, Ankara, Turkey; Department of Medical Oncology, Ankara Numune Hospital, Ankara, Turkey (OA); Department of Clinical Oncology, Hospital Maternidade De Campinas, Campinas, Brazil (MZB); Department of Neurosurgery Baylor College of Medicine, Houston, TX (MAA)
Correspondence to: Kadri Altundag, MD, 8181 Fannin St., No. 728, Houston, TX 77054 (e-mail: drkadri{at}usa.net).
We read with interest the article by Schrag et al. (1) regarding cetuximab and symptomatic hypomagnesemia. They reported that patients treated with cetuximab, a monoclonal antibody against the epithelial growth factor receptor (EGFR), occasionally developed a magnesium-wasting syndrome with inappropriate urinary excretion. They hypothesized that blockade of the EGFR in the nephron reversibly impaired function of the proteins involved in active transport of extracellular magnesium, resulting in hypomagnesemia. Two EGFR tyrosine kinase inhibitors, gefitinib (ZD1839, Iressa) and erlotinib (OSI-774, Tarceva), also block EGFR signaling, and so these two agents may also have the potential to impair magnesium metabolism in the nephron. However, to date there is no report published in the English literature related to an association between these two EGFR tyrosine kinase inhibitors and hypomagnesemia. Among the inactive gradients in gefitinib and erlotinib tablets is magnesium stearate (2,3). Although these two agents may exert some EGFR blockage in the nephron resulting in hypomagnesemia, as does cetuximab, this deficiency may be balanced by magnesium stearate supplementation present in the tablets of these agents. These assumptions need to be clarified by further studies.
NOTES
Editor's note: Dr. Schrag declined our invitation to respond.
REFERENCES
(1) Schrag D, Chung KY, Flombaum C, Saltz L. Cetuximab therapy and symptomatic hypomagnesemia. J Natl Cancer Inst 2005;97:1221–4.
(2) Tarceva package insert. Available at: http://www.tarceva.com/tarceva/professional/prescribing/PI.jsp. [Last accessed: August 30, 2005.]
(3) PDR information for Iressa Tablets. Available at: http://www.drugs.com/PDR/Iressa_Tablets.html. [Last accessed: August 30, 2005.]
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