Magnesium Sulfate

Question 1

Generic Name:

Answer 1

Magnesium Sulfate

Question 2

Supplied:

Answer 2

1g/2mL vial

Question 3

Class:

Answer 3

Electrolyte, tocolytic

Question 4

Mechanism of Action: Pharmacology:

Answer 4

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.

Question 5

Mechanism of Action: Clinical:

Answer 5

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

Question 6

Indications and Field Use:

Answer 6

- Torsade de pointes, drug of choice
- Hypomagnesemia
- Pre-term labor (PTL)
- Pregnancy-induced hypertension (PIH, toxemia of pregnancy, pre-eclampsia and/or eclampsia).
- Hyperreactive Airway - Severe Asthma

Question 7

Contraindications:

Answer 7

- 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.

Question 8

Adverse Reactions:

Answer 8

CV: Hypotension (may be transient), flushing, circulatory collapse, depressed cardiac function, heart block, asystole, smooth muscle relaxant (antihypertensive effects).

Resp: 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

Meta: Hypocalcemia, hypermagnesemia

Question 9

Incompatibilities/Drug Interactions:

Answer 9

Concurrent digitalization increases danger of dysrhythmias

Question 10

Adult Dosage: Torsades de Pointes:

Answer 10

1 - 2g IV diluted in 50 - 100 mL NS or D5W administered over 1 to 2 minutes, followed by the same amount infused over 1 hour.

Question 11

Adult Dosage: Hypomagnesemia:

Answer 11

Dilute 1 - 2g in 50 - 100 mL NS or D5W administered IV push over 5 to 60 minutes.

Question 12

Adult Dosage: Respiratory/Severe Asthma:

Answer 12

Initial Infusion (field) 2g 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.

Question 13

Adult Dosage: Pre-term labor (PTL):

Answer 13

• Initial bolus (Field and Interfacility): 4 - 6g over 15 to 20 minutes (Suggested method is the addition of 4g to 100 mL D5W, LR or NS. Resultant concentration is 40 mg/mL.)
• Maintenance Infusion (Interfacility only): 1-4g/hour infusion rate. (Suggested method for treatment of premature labor is to follow initial bolus with infusion of 2g/hr which may be continued until uterine contractions are reduced to < 1 every 10 minutes. Then, infusion is decreased to 1g/hr and continued for 24 to 72 hrs. One method for mixing infusion is the addition of 40g to 1000 mL LR. Resultant concentration equals 40 mg/ml. If this concentration is run at 50 mL/hr, Magnesium Sulfate delivered equals 2g/hr).

Question 14

Adult Dosage: Pregnancy induced hypertension, pre-eclampsia/eclampsia, (PIH):

Answer 14

• Initial bolus (Field and Interfacility): 3 - 6g over 10 to 15 minutes (Suggested method is the addition of 4g to 100 mL D5W, LR or NS. Resultant concentration is 40 mg/mL).
• Maintenance Infusion (Interfacility only): Follow bolus with 1 - 3g/hour infusion rate. (Same mixture as for PTL). Rebolus: In an eclamptic emergency may rebolus with Magnesium Sulfate, 2 - 4g depending on patient size (mixed as an initial bolus) over 10-15 minutes if respirations >12/minute and urine output >30 ml/hr.

Question 15

Routes of Administration:

Answer 15

• IV infusion

- IO

Question 16

Onset of Action:

Answer 16

• Seconds

- 20 minutes for IV infusion (respiratory)

Question 17

Peak Effects:

Answer 17

Not known

Question 18

Duration of Action:

Answer 18

24 hours or greater

Question 19

Arizona Drug Box Minimum Supply:

Answer 19

5g

Question 20

Special Notes:

Answer 20

- 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).

Question 21

Special Notes Continued:

Answer 21

- 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 mL/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