Internal Medicine

0521779407-14 CUNY1086/Karliner 0 521 77940 7 June 4, 2007 21:16

Magnesium Deficiency 941

specific treatment

■When symptoms or hypomagnesemia with continued losses

➣If acute symptoms (seizure, arrhythmia): 2 g 50% MgSO4 solution

IV over 5 minutes (16 mEq elemental Mg), followed by 32–48

mEq IV per 24 hours for several days); monitor renal function

and serum Mg (level will normalize before intracellular stores

are repleted)

➣No IV bolus needed if no acute symptoms

■Oral therapy: e.g., Mg oxide 400 mg p.o. tid, Milk of Magnesium 5 cc

tid; Mg-chloride and Mg-gluconate therapeutic options

side effects & contraindications

■IV magnesium

■Side effects: uncommon unless excess doses given; with level >4

mEq/L, deep tendon reflexes disappear, PR interval prolongs; fur-

ther elevations cause hypotension, respiratory depression, coma at

10–12 mEq/L

■Contraindications

■absolute: elevated serum magnesium level, renal failure

■relative: hypotension (replacement doses of IV Mg may drop systolic

BP 5 mm Hg)

■Oral magnesium

■side effects: diarrhea (minimize by dividing dose into more frequent

intervals, smaller amount)

follow-up

During Rx

■Monitor BP, heart rate, DTR, serum creatinine, daily serum Mg level

(may need to continue slow IV Mg infusion for several days to replete

stores even if level normalizes, if patient not eating)

■Correct cause of Mg deficiency; long-term, potassium-sparing

diuretics are also magnesium-sparing (e.g., aldactone, amiloride)

complications & prognosis

■If deficiency uncorrected, symptoms can persist – risk of death from

untreated seizures, cardiac arrhythmias

Prognosis

■Symptoms of Mg deficiency completely reversible if Mg deficiency

is corrected