Hypomagnesemia is often neither adequately replaced nor appropriately followed in hospitalized patients. In particular, because the average magnesium deficiency in hypomagnesemia is 50–100 mEq, a single parenteral dose of 2 g of magnesium sulfate is woefully inadequate, not only because it contains just 16.2 mEq of magnesium, but also because half of it will typically be lost in the urine. Moreover, because serum magnesium requires 3–4 days to reach tissue equilibration, “normal” magnesium levels in the midst of active repletion do not accurately reflect magnesium stores and should generally be ignored. Suspecting that these principles of magnesium management are not followed, we sought to describe the adequacy of replacement and the appropriateness of follow‐up testing among general medicine inpatients.


Our study sample was drawn from 13,191 hospitalizations to the general medicine service of a public teaching hospital from May 2009, to July 2010. The inclusion criterion was an initial serum magnesium level < 1.8 mg/dL, and the exclusion criterion was a glomerular filtration rate (GFR) < 30 mL/min using the Modification of Diet in Renal Disease formula. We calculated the total inpatient magnesium dose from published data for each formulation. The magnesium replacement dose was deemed adequate if the total dose was >50 mEq, a low‐end estimate for a 50‐kg hypomagnesemic patient. We used the Wilcoxon rank sum test to test for differences in redosing durations because these data were nonparametric.


Of 13,191 hospitalizations to the general medicine service during the study period, at least 1 serum magnesium level was drawn in 6173. Among these 6173 hospitalizations, 1851 met the inclusion criterion for hypomagnesemia, but 331 were excluded due to reduced GFRs. Thus, the primary study cohort was 1520 patients. No magnesium supplements were given to 45% (690 of 1520), and only 21% (321 of 1520) received adequate replacement throughout their hospitalizations. Among 34 patients with severe hypomagnesemia (initial serum magnesium level < 1.2 mg/dL), 64% (22 of 34) received adequate replacement. Repeat magnesium levels were performed during hospitalization after a median of 24 hours (IQR, 18–40 hours) after initial magnesium doses. Patients whose serum magnesium values returned to normal were redosed a median of 20 hours later than patients whose values remained decreased (P < 0.0001), suggesting that prescribing physicians delayed treatment because of deceptively normal serum magnesium levels.


Magnesium replacement doses were inadequate in 79% of patients. Repeat magnesium testing occurred too soon after initial replacement doses and may have inappropriately delayed further treatment. To address these problems, we plan quality improvement initiatives that incorporate physician education on the principles of hypomagnesemia replacement.


A. Katz ‐ none; S. Punj ‐ none; N. Singh ‐ none; A. Abegunde ‐ none; D. Avila ‐none; A. Xintavelonis ‐ none; B. Ninan ‐ none; M. Qattan ‐ none; B. Lucas ‐none