Magnesium Sulfate

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GENERIC NAME: MAGNESIUM SULFATE BRAND NAME: Magnesium Sulfate CLASS: Electrolyte, tocolytic

Mechanism of Action:

Pharmacology: Second most plentiful intracellular cation; essential to enhance intracellular potassium replenishment and activity of many enzymes; important role in neurochemical transmission and muscular excitability (may decrease acetylcholine released by nerve impulses); decreases myocardial irritability and neuromuscular irritability.

Clinical: Cardiac-reduces ventricular irritability, especially when associated with hypomagnesemia; inhibition of muscular excitability.

Indications and Field Use:

• Torsade de pointes, drug of choice

• VF/Pulseless VT refractory to lidocaine and/or amiodarone

• Hypomagnesemia

• Pre-term labor (PTL)

• Pregnancy-induced hypertension (PIH, toxemia of pregnancy, pre-eclampsia and/or eclampsia).

• Hyperreactive Airway - Severe Asthma Contraindications:

• Hypermagnesemia

• Use cautiously in patients with impaired renal function and pre-existing heart blocks (relative).

Precautions: Caution when used with barbituates, narcotics, or other hypnotics (or system anesthetics) in conjunction with Magnesium Sulfate due to the additive central depressive effects of magnesium. Adverse Reactions:

Cardiovascular: hypotension (may be transient), flushing, circulatory collapse, depressed cardiac function, heart block, asystole, smooth muscle relaxant (antihypertensive effects). Respiratory: respiratory depression and/or paralysis. This adverse reaction may occur in both mother and/or infant during or up to 24 hours after the administration of Magnesium Sulfate. CNS: sweating, drowsiness, hypothermia, depressed reflexes progressing to flaccidity and paralysis. This adverse reaction may occur in both mother and/or infant during the administration of or up to 24 hours after the administration of Magnesium Sulfate. GI: nausea GU: mild diuretic Metabolic: hypocalcemia, hypermagnesemia

NOTES ON ADMINISTRATION

Incompatibilities/Drug Interactions: Concurrent digitalization increases danger of dysrhythmias

Adult Dosage:

Cardiac:

• VF/Pulseless VT: 1-2 Gm IV diluted in 50-100 ml NS or D5W, administered over 1-2 minutes.

• Torsade de pointes: 1-2 Gm IV diluted in 50-100 ml NS or D5W administered over 1-2 minutes, followed by the same amount infused over 1 hour.

• Hypomagnesemia: Dilute 1-2 Gm in 50-100 ml NS or D5W administered IV push over 5-60 minutes.

• Respiratory/Severe Asthma: Initial Infusion (field) 2 Gm

Magnesium Sulfate mixed in 50 ml NS or D5W to be infused IV using microdrip tubing over 5 to 10 minutes. Stop infusion if hypotension, respiratory depression or bradycardia develop. Pregnancy: Pre-term labor (PTL): Initial bolus (Field and Interfacility): 4-6 Gm over 15-20 minutes (Suggested method is the addition of 4 Gm to 100 ml D5W, LR or NS. Resultant concentration is 40 mg/ml.) Maintenance Infusion (Interfacility only): 1-4 Gm/hour infusion rate. (Suggested method for treatment of premature labor is to follow initial bolus with infusion of 2 Gm/hr which may be continued until uterine contractions are reduced to < 1 every 10 minutes. Then, infusion is decreased to 1 Gm/hr and continued for 24-72 hrs. One method for mixing infusion is the addition of 40 Gm to 1000 ml LR. Resultant concentration equals 40 mg/ml. If this concentration is run at 50 ml/hr, Magnesium Sulfate delivered equals 2 Gm/hr). Pregnancy induced hypertension, pre-eclampsia/eclampsia, (PIH): Initial bolus (Field and Interfacility): 3-6 Gm over 10-15 minutes (Suggested method is the addition of 4 Gm to 100 ml D5W, LR or NS. Resultant concentration is 40 mg/ml). Maintenance Infusion (Interfacility only): Follow bolus with 1-3 Gm/hour infusion rate. (Same mixture as for PTL). Rebolus: In an eclamptic emergency may rebolus with Magnesium Sulfate, 2-4 Gm depending on patient size (mixed as an initial bolus) over 10-15 minutes if respirations >12/minute and urine output >30 ml/hr.

Routes of Administration:

IV infusion IO

Onset of Action:

Seconds 20 minutes for IV Infusion (respiratory)

Peak Effects:

Not known

Duration of Action:

24 hours or greater

Dosage Forms/Packaging:

1 Gm/2 cc vials (0.5 Gm/cc) 5 Gm/10 cc vials (0.5 Gm/cc)

Arizona Drug Box Supply Range:

5 Gm

Special Notes:

• O2 should be administered to patients receiving Magnesium Sulfate.

• For specific emergencies:

o OB emergencies maintenance infusions of Magnesium Sulfate should be administered by infusion pump to prevent toxicity. Therefore, loading bolus therapy only, using a minimum of microdrip tubing is recommended for field to hospital intervention for OB indications.

o Interfacility transfers may include a loading dose followed by a maintenance infusion of Magnesium Sulfate which requires an infusion pump.

o Respiratory (Asthma) emergencies: Magnesium Sulfate follows Albuterol & Atrovent SVN and administration of 0.3 IM Epi (1:1000).

• For IV/IO infusions (respiratory) start and stop times should be closely monitored and documented per administration guidelines of 20 minutes or greater.

• Transport gravid patients lying or tilted to left side to prevent

restricting venous return to heart.

• Use cautiously in patients with impaired renal function, pre- existing heart blocks and women in labor.

• Evaluate cardiac status and ECG assessing for prolonged PR and widened QRS intervals.

• Do not delay intubation or ventilation for Magnesium Sulfate administration in patients suffering severe asthma episode.

• Keep Calcium Chloride (10%) 10 ml available to reverse magnesium toxicity. See: Calcium Chloride profile. Use extreme caution if the patient is on digoxin.

• Monitor vital signs every 15 minutes in patients receiving Magnesium Sulfate infusion. If respirations less than 12/min, discontinue Magnesium Sulfate infusion, notify medical direction.

• Hourly intake and output should be monitored on long transport; urine output should be greater than 30 cc/hr.

• When given to toxemic mothers within 24 hours before delivery observe newborn for signs/symptoms of Magnesium Sulfate toxicity (neuromuscular and/or respiratory depression).

• Interfacility maternal transport teams are recommended and available for the transport of patients requiring continuous IV infusions of Magnesium Sulfate.

• In treatment of seizures associated with PIH it may be necessary to use an anticonvulsant such as diazepam.

• Eclampsia may occur up to six weeks after delivery 

© Matt Dillard 2012