A 58-year-old woman with history of diabetes on insulin presented to the emergency department with fatigue and generalized weakness for several weeks. She reported taking omeprazole for the last month for “heart burn.” She was also undergoing chemotherapy for colon cancer that included cetuximab.
Laboratory results were significant for a low serum magnesium level (0.9 mg/dL) and hyperglycemia (blood glucose level 360 mg/dL).The rest of the laboratory findings were unremarkable. An EKG showed QRS widening. She was given magnesium gluconate infusion and insulin. Omeprazole was withheld. Over the next 2 days, the patient’s serum magnesium level repeatedly dropped and was highly dependent on magnesium repletion through infusion and oral tablets. Blood glucose was well controlled with insulin. Additional workup for hypomagnesemia was performed and revealed:
- Serum electrolytes: magnesium 1.2 mg/dL, sodium 133 mEq/L, potassium 3.5 mEq/L, calcium 8.9 mg/dL, phosphorus 3.2 mg/dL
- Serum creatinine: 0.9 mg/dL
- Fractional excretion of magnesium (FEMag) 6%
- 24-hour urinary magnesium excretion 230 mg
- Urinalysis negative for blood or protein