How is hypomagnesemia treated?
Patients with severe symptomatic hypomagnesemia (i.e., seizures, tetany, or arrhythmia) need intravenous (IV) magnesium. One to 2 g of magnesium sulfate (8 to 17 mEq of magnesium) can be given by rapid IV push in patients in cardiac arrest or over an hour in patients with a pulse. This should be followed by a longer, slow infusion of another 4 to 8 g (33 to 66 mEq) of magnesium over 24 hours. This continuous infusion can be repeated safely for up to 3 consecutive days in order to ensure adequate repletion of intracellular and bone stores. Doses should be lowered in chronic kidney disease. Intravenous magnesium inhibits magnesium reabsorption in the loop of Henle, so patients will have increased kidney magnesium wasting during treatment. Up to 50% of infused magnesium will be excreted within a day of the infusion.
Magnesium sulfate increases kidney losses of potassium. This can exacerbate hypokalemia, so concomitant therapy with potassium should be considered. In addition, magnesium sulfate can lower ionized calcium.
Patients with asymptomatic or mildly symptomatic hypomagnesemia can be treated with oral magnesium replacement. Patients should be prescribed 240 to 1000 mg of elemental magnesium daily, in divided doses. Oral magnesium can cause diarrhea, worsening the hypomagnesemia, so the dose needs to be adjusted to avoid this side effect.
Here is the table with the list of oral magnesium preparations.
Oral Magnesium Preparations
|Magnesium oxide (Uro-Mag)||84.5 mg | 7.0 mEq | 3.5 mmol|
|Magnesium chloride (Slow-Mag)||71.0 mg | 6.0 mEq | 3.0 mmol|
|Magnesium l-lactate (MAG-TAB SR)||84.0 mg | 7.0 mEq | 3.5 mmol|
|Magnesium aspartate||65.0 mg | 5.4 mEq | 2.7 mmol|
Patients who cannot tolerate oral magnesium can be replaced with intravenous magnesium. Doses range from 1 to 8 g over 12 to 24 hours, depending on the severity of hypomagnesemia
Empirical Treatment of Hypomagnesemia
Originally published in Kraft, M. D., Btaiche, I. F., Sacks, G. S., et al. (2005). Treatment of electrolyte disorders in adult patients in the intensive care unit. American Journal of Health-System Pharmacy, Inc. 62(16), 1663-1682. All rights reserved. Reprinted with permission. (R1707).
|Severity||Serum Magnesium Concentration (mg/dL)||IV Magnesium Replacement DOSE a , b|
|Mild to moderate||1.0–1.5||8–32 meq magnesium (1–4 g magnesium sulfate), up to 1.0 meq/kg|
|Severe||<1.0||32–64 meq magnesium (4–8 g magnesium sulfate), up to 1.5 meq/kg|
a In patients with normal renal function; patients with renal insufficiency should receive ≤50% of the initial empirical dose. Maximum rate of infusion = 8 meq magnesium per hour (1 g magnesium sulfate per hour), up to 100 meq magnesium (approximately 12 g magnesium sulfate) over 12 hours if asymptomatic; up to 32 meq magnesium (4 g magnesium sulfate) over 4–5 minutes in severe symptomatic hypomagnesemia. 1 g magnesium sulfate = 8.1 meq magnesium.
b The authors suggest using adjusted body weight (AdjBW) in patients who are significantly obese (weight of >130% of ideal body weight [IBW] or have a body mass index of ≥30 kg/m2): AdjBW (men) = ([wt (kg) – IBW (kg)] × 0.3) + IBW; AdjBW (women) = ([wt (kg) – IBW (kg)] × 0.25) + IBW.