The proton pump inhibitor (PPI) Nexium (esomeprazole) is often prescribed for gastroesophageal reflux disease (GERD), a condition not uncommon among afibbers. Dutch physicians recently reported a case of a 76-year-old woman who presented with muscle cramps and lethargy. Blood analysis showed evidence of very low levels of magnesium (0.18 mmol/L), calcium (1.26 mmol/L), potassium (3.2 mmol/L), and parathyroid hormone (0.9 pmol/L). She was started on intravenous calcium and magnesium supplementation. After 3 days her levels of magnesium, calcium, potassium and parathyroid hormone normalized and her symptoms improved. The Nexium was discontinued and magnesium and calcium levels remained in the normal range. Subsequently, GERD symptoms reappeared and Nexium therapy was reinstated. Within 4 weeks the blood (serum) level of magnesium dropped to 0.4 mmol/L (normal range of 0.65 - 1.05 mmol/L). The Dutch physicians conclude that the use of PPIs is associated with a substantial risk of inducing severe magnesium deficiency.

Kuipers, et al. Hypomagnesaemia due to use of proton pump inhibitors � a review. Netherlands Journal of Medicine, Vol. 67, May 2009, pp. 169-72