Effects of Intravenous Magnesium Sulfate on the QT Interval in Patients Receiving Ibutilide

Michael F. Caron, Pharm.D., Jeffrey Kluger, M.D., James P. Tsikouris, Pharm.D., Arnold Ritvo, M.D., James S. Kalus, Pharm.D., C. Michael White, Pharm.D.

Disclosures

Pharmacotherapy. 2003;23(3)

Conclusion

Our study results suggest that prophylactic administration of intravenous magnesium sulfate prevents increases in the QT and QTc interval 30 minutes after the last infusion of ibutilide in patients with atrial fibrillation or flutter. No other changes in standard electrocardiographic variables, QT or QTc interval dispersion, or heart rate were observed.

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Address reprint requests to C. Michael White, Pharm.D., Drug Information Center, Hartford Hospital, 80 Seymour Street, Hartford, CT 06102-5037; e-mail: cmwhite@harthosp.org.

Cite this: Effects of Intravenous Magnesium Sulfate on the QT Interval in Patients Receiving Ibutilide - Medscape - Mar 01, 2003.

Table 1. Patient Demographics
Characteristic	Magnesium Sulfate Group (n=11)	Placebo Group (n=9)
	Mean ± SD
Age (yrs)	70 ± 12	74 ± 16
Weight (kg)	84 ± 27	85 ± 11
Baseline magnesium level (mg/dl)	2.1 ± 0.3	2.1 ± 0.27
	No. (%)
M/F	7 (64)/4 (36)	5 (56)/4 (44)
Atrial fibrillation	6 (55)	6 (67)
Atrial flutter	5 (45)	3 (33)
Overall CDV with ibutilide	6 (55)	5 (56)
CDV with ibutilide 1 mg (n=6)	2/2 (100)	4/4 (100)
CDV with Ibutilide 2 mg (n=14)	4/9 (44)	1/5 (20)

Table 2. QT Interval Variables
Time Point	QT Interval (msec)	QTc Interval (msec)	QT Increase from Baseline (msec)	QTc Increase from Baseline (msec)
Baseline
Placebo	348.1 ± 36.4	428.6 ± 31.5	--	--
Magnesium sulfate	347.5 ± 47.7	430.4 ± 23.0	--	--
30 minutes after treatment
Placebo	448.8 ± 84.7^a	503.7 ± 68.6^a	100.7 ± 88.0	75.1 ± 70.3
Magnesium sulfate	394.7 ± 72.4	449.5 ± 50.8	47.3 ± 82.6	19.2 ± 51.6^b
60 minutes after treatment
Placebo	405.2 ± 83.9	458.8 ± 70.4	57.1 ± 76.3	30.2 ± 84.2
Magnesium sulfate	389.8 ± 76.1	448.8 ± 40.8	42.4 ± 75.9	18.5 ± 30.6

Table 2. QT Interval Variables
Time Point	QT Interval (msec)	QTc Interval (msec)	QT Increase from Baseline (msec)	QTc Increase from Baseline (msec)
Baseline
Placebo	348.1 ± 36.4	428.6 ± 31.5	--	--
Magnesium sulfate	347.5 ± 47.7	430.4 ± 23.0	--	--
30 minutes after treatment
Placebo	448.8 ± 84.7^a	503.7 ± 68.6^a	100.7 ± 88.0	75.1 ± 70.3
Magnesium sulfate	394.7 ± 72.4	449.5 ± 50.8	47.3 ± 82.6	19.2 ± 51.6^b
60 minutes after treatment
Placebo	405.2 ± 83.9	458.8 ± 70.4	57.1 ± 76.3	30.2 ± 84.2
Magnesium sulfate	389.8 ± 76.1	448.8 ± 40.8	42.4 ± 75.9	18.5 ± 30.6

Table 2. QT Interval Variables
Time Point	QT Interval (msec)	QTc Interval (msec)	QT Increase from Baseline (msec)	QTc Increase from Baseline (msec)
Baseline
Placebo	348.1 ± 36.4	428.6 ± 31.5	--	--
Magnesium sulfate	347.5 ± 47.7	430.4 ± 23.0	--	--
30 minutes after treatment
Placebo	448.8 ± 84.7^a	503.7 ± 68.6^a	100.7 ± 88.0	75.1 ± 70.3
Magnesium sulfate	394.7 ± 72.4	449.5 ± 50.8	47.3 ± 82.6	19.2 ± 51.6^b
60 minutes after treatment
Placebo	405.2 ± 83.9	458.8 ± 70.4	57.1 ± 76.3	30.2 ± 84.2
Magnesium sulfate	389.8 ± 76.1	448.8 ± 40.8	42.4 ± 75.9	18.5 ± 30.6

Table 3. Number (%) of Patients with QTc Interval Values Increasing Greater Than 30 and 60 msec and QTc Interval Values of More Than 500 msec at Any Follow-up Time Point
QTc Interval (msec)	Magnesium Sulfate Group (n=11)	Placebo Group (n=9)	p Value
Increase > 30	3 (27)	7 (78)	0.07
Increase > 60	3 (27)	6 (67)	0.175
Value > 500	2 (18)	5 (56)	0.160

Table 4. QT Dispersion Interval Variables
Time Point	QT Dispersion (msec)	QTc Dispersion (msec)
Baseline
Placebo	54.4 ± 23.0	61.6 ± 56.2
Magnesium sulfate	63.6 ± 28.7	68.7 ± 38.5
30 minutes after treatment
Placebo	74.4 ± 14.2	66.7 ± 43.0
Magnesium sulfate	85.5 ± 38.8	98.6 ± 50.6
60 minutes after treatment
Placebo	84.4 ± 45.8	90.9 ± 57.2
Magnesium sulfate	69.1 ± 34.5	77.3 ± 46.1

Table 1. Patient Demographics
Characteristic	Magnesium Sulfate Group (n=11)	Placebo Group (n=9)
	Mean ± SD
Age (yrs)	70 ± 12	74 ± 16
Weight (kg)	84 ± 27	85 ± 11
Baseline magnesium level (mg/dl)	2.1 ± 0.3	2.1 ± 0.27
	No. (%)
M/F	7 (64)/4 (36)	5 (56)/4 (44)
Atrial fibrillation	6 (55)	6 (67)
Atrial flutter	5 (45)	3 (33)
Overall CDV with ibutilide	6 (55)	5 (56)
CDV with ibutilide 1 mg (n=6)	2/2 (100)	4/4 (100)
CDV with Ibutilide 2 mg (n=14)	4/9 (44)	1/5 (20)

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Effects of Intravenous Magnesium Sulfate on the QT Interval in Patients Receiving Ibutilide

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