Comparison of Intravenous and Oral Magnesium Replacement in Hospitalized Patients With Cardiovascular Disease

Brent N. Reed; Su Zhang, J. S. Marron; Deborah Montague

Am J Health Syst Pharm. 2012;69(14):1212-1217.

Conclusion

A comparison of 24-hour courses of magnesium replacement therapy showed that magnesium sulfate 2 g i.v. was associated with larger changes in SMC than magnesium oxide 800, 1200, or 1600 mg orally when the baseline SMC was 1.4–1.8 mg/dL. At baseline SMCs of 1.4–1.8 mg/dL, oral magnesium oxide provided a consistent median increase in SMC of 0.1 mg/dL. The change in the number of bowel movements did not differ significantly between courses of i.v. magnesium sulfate and oral magnesium oxide.

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Table 1. Characteristics of Courses of Magnesium Replacement Therapy ^a
Characteristic	I.V. Magnesium Sulfate (n = 188)	Oral Magnesium Oxide (n = 164)
No. (%) courses with male pt	93 (49.5)	93 (57.3)
Mean ± S.D. pt age (yr)	58 ± 15	56 ± 14
Mean ± S.D. pt weight (kg)	83.9 ± 32.6	85.9 ± 24.1
Mean ± S.D. creatinine clearance of pt (mL/min)^b	94.2 ± 28.2	86.7 ± 27.6^c
Mean ± S.D. total magnesium dose (meq)	16.2 ± 0.0	46.4 ± 10.8^c
Mean ± S.D. baseline SMC (mg/dL)	1.65 ± 0.13	1.78 ± 0.13
Median time (interquartile range) between course completion and blood sampling for SMC (hr)	18.00 (15.75–20.00)	8.25 (7.00–17.81)^c
No. (%) courses with pt receiving ≥1 medication affecting magnesium absorption^d	136 (72.4)	104 (63.4)
No. (%) courses with pt receiving ≥1 medication affecting magnesium excretion^e	67 (36.0)	63 (38.4)

^a SMC = serum magnesium concentration.
^bEstimated with the method of Cockcroft and Gault.⁷
^c p < 0.05 for comparison with i.v. magnesium sulfate.
^dIncludes proton pump inhibitors, histamine H₂-receptor antagonists, vitamin D, and calcium supplements.
^eIncludes diuretics, calcineurin inhibitors, aminoglycosides, and amphotericin B.

Table 2. Change in Serum Magnesium Concentration (SMC) After Courses of I.V. Magnesium Sulfate or Oral Magnesium Oxide
Baseline SMC (mg/dL)	I.V. Magnesium Sulfate			Oral Magnesium Oxide			p
Baseline SMC (mg/dL)	n	Mean ± S.D. Change (mg/dL)	Median Change (mg/dL)	n	Mean ± S.D. Change (mg/dL)	Median Change (mg/dL)	p
1.2	2	0.50 ± 0.00	0.5	1	0.00 ± 0.00	0.0	0.0
1.3	2	0.40 ± 0.10	0.4	1	0.40 ± 0.00	0.4	0.5
1.4	15	0.39 ± 0.19	0.4	12	0.14 ± 0.22	0.1	0.003
1.5	20	0.27 ± 0.18	0.3	15	0.07 ± 0.11	0.1	<0.001
1.6	39	0.27 ± 0.19	0.2	23	0.11 ± 0.16	0.1	<0.001
1.7	52	0.21 ± 0.19	0.2	44	0.10 ± 0.15	0.1	<0.001
1.8	58	0.19 ± 0.19	0.2	68	0.09 ± 0.16	0.1	0.001

Table 3. Association Between Total Magnesium Dose and Change in Serum Magnesium Concentration (mg/dL)
Magnesium Dose	No. Courses	Mean ± S.D. Change	Median Change
I.V. Magnesium Sulfate
2 g	188	0.24 ± 0.2	0.2
Oral Magnesium Oxide
800 mg	127	0.10 ± 0.16^a	0.1
1200 mg	18	0.11 ± 0.15^b	0.1
1600 mg	19	0.05 ± 0.14^a	0.1

^a p < 0.001 for comparison with i.v. magnesium sulfate.
^b p = 0.003 for comparison with i.v. magnesium sulfate.

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