MAGNESIUM SULFATE-D5W

General Administration Information
For storage information, see the specific product information within the How Supplied section.

Route-Specific Administration

Oral Administration
Oral Solid Formulations
-Oral tablets or capsules: Administer with a full glass of water.
-Delayed-release or enteric-coated tablets: Administer whole. Do not cut, crush, or chew.

Oral Liquid Formulations
-Oral solutions: Mix magnesium with water.
-For neonates, the parenteral solution has been given orally by diluting the solution in feedings.



Injectable Administration
-Visually inspect parenteral products for particulate matter and discoloration prior to administration whenever solution and container permit.
Intravenous Administration
Dilution
-Dilute in compatible diluent (i.e., 0.9% NaCl Injection, 5% Dextrose Injection, 10% Dextrose Injection, Lactated Ringer's Injection).
-Magnesium sulfate concentration once diluted should generally not exceed 200 mg/mL (20%).

Intermittent IV Infusion
-According to the manufacturer, the rate should not exceed 150 mg/minute, except for emergent indications. Rapid infusion rates may exceed the urinary magnesium excretion threshold resulting in hypermagnesemia, which may increase the risk of adverse effects.
-Infusion rates in children are dependent upon the clinical situation:-For asymptomatic hypomagnesemia, infusions are generally given over 30 to 60 minutes.
-For pulseless torsades, give by rapid bolus administration over several minutes.
-For symptomatic hypomagnesemia/torsades with pulses, infuse over 10 to 20 minutes.
-For status asthmaticus, infuse over 15 to 30 minutes.

-During IV magnesium therapy, an intravenous calcium preparation (e.g., calcium gluconate) should be readily available as a reversal agent in case symptomatic hypermagnesemia occurs.

Intramuscular Administration
-For infants and young children, magnesium sulfate concentrations should not exceed 200 mg/mL (20%). For older children, the FDA-approved labeling states that a 50% concentration (500 mg/mL) may be used.
-Inject deeply into a large muscle mass (e.g., anterolateral thigh or deltoid [children and adolescents only]). Aspirate prior to injection to avoid injection into a blood vessel.

Other Injectable Administration
Intraosseous Administration
NOTE: Magnesium sulfate is not FDA-approved for intraosseous administration.
-During cardiopulmonary resuscitation, the same dosage may be given via intraosseous infusion when IV access is not available.



Inhalation Administration
Oral Inhalation Administration
NOTE: Magnesium sulfate is not FDA-approved for oral inhalation administration.
-Although evidence is limited, studies report administering injectable isotonic magnesium sulfate, sometimes mixed with albuterol or ipratropium, via a nebulizer for the treatment of acute asthma.
-One study reports using isotonic magnesium in the form of a 6.3% solution of magnesium heptahydrate, which is equivalent to 3.18% anhydrous magnesium sulfate.

The most frequently reported adverse reactions of parenteral magnesium sulfate are hypermagnesemia and signs and symptoms of magnesium toxicity. These reactions are characterized by flushing, diaphoresis, hypotension, depressed deep tendon reflexes, muscle paralysis, weakness, hypothermia, circulatory collapse, CNS depression including impaired cognition (stupor), and cardiac or respiratory depression. Deep tendon reflexes may be decreased at serum magnesium concentrations of 4 mEq/L resulting in muscle weakness and hyporeflexia; patellar reflexes usually become hypoactive or disappear at magnesium concentrations > 9 mEq/L. Respiratory depression or cardiac conduction abnormalities (e.g., AV block) are noted most commonly at serum magnesium concentrations >= 10 mEq/L. Magnesium levels > 14 mEq/L may be fatal due to respiratory arrest, or from cardiac arrest secondary to complete heart block. Magnesium toxicity (conduction abnormalities or respiratory depression) can be reversed by discontinuation of the magnesium therapy and the use of intravenous calcium gluconate. Rapid administration of intravenous magnesium sulfate may result in clinically significant hypotension, bradycardia, or asystole and should be avoided. Injection site reaction may occur.

Injectable magnesium formulations contain aluminum. Thus, aluminum toxicity may occur with prolonged administration in high-risk patients, including those with renal impairment and premature neonates. Premature neonates are at particular risk for aluminum toxicity because of immature renal function and they require large amounts of calcium and phosphate solutions, which contain aluminum. Research indicates that patients with renal impairment, who receive parenteral aluminum at rates greater than 4 to 5 mcg/kg/day, may develop aluminum toxicity (central nervous system and bone toxicity). Tissue loading may occur at lower administration rates.

The most common adverse reaction associated with oral magnesium salts is diarrhea. Dividing large doses into multiple daily doses may minimize the frequency of diarrhea.

Parenteral magnesium should be avoided in patients with AV block because it can exacerbate this condition. If parenteral treatment with magnesium salts is necessary, magnesium should be infused at a slower rate and magnesium levels monitored closely. Cardiac disease in the form of myocardial damage generally is considered a contraindication of magnesium salts; however, magnesium sulfate has been used in acute myocardial infarction patients to reduce reperfusion injury, decrease infarct size, and to prevent arrhythmias. Magnesium salts should be used with caution in patients with electrolyte imbalance; do not use magnesium salts in patients with preexisting hypermagnesemia.

Magnesium salts should be used with caution in patients with renal disease or renal failure. Magnesium salts are renally eliminated, so patients with renal impairment have an increased risk of developing magnesium toxicity from decreased excretion of magnesium. Up to 30% to 40% of an orally administered dose is absorbed systemically. Monitor magnesium serum concentrations frequently in patients with renal insufficiency. Magnesium sulfate injection contains aluminum (12,500 mcg/L or less). Thus, aluminum may reach toxic levels with prolonged administration in patients with renal impairment. Research indicates that patients with renal impairment who receive parenteral aluminum at rates greater than 4 to 5 mcg/kg/day may accumulate aluminum at concentrations associated with central nervous system and bone toxicity. Tissue loading may occur at lower administration rates.

Magnesium sulfate injection contains aluminum (<= 12,500 mcg/L). Premature neonates are at particular risk for aluminum toxicity because of immature renal function and they require large amounts of calcium and phosphate solutions, which also contain aluminum. Research indicates that patients with renal impairment, including neonates with immature renal function, who receive parenteral aluminum at rates greater than 4-5 mcg/kg/day may accumulate aluminum at concentrations associated with CNS and bone toxicity. Tissue loading may occur at lower administration rates.

All neonates with a history of prolonged in utero exposure to parenteral magnesium sulfate should be monitored carefully for hypocalcemia and bone abnormalities. Continuous administration of magnesium sulfate as a tocolytic during pregnancy beyond 5-7 days has resulted in bone abnormalities, including skeletal demineralization, osteopenia, and neonatal fracture. The shortest duration of therapy that can result in fetal harm is unknown. In a review of the FDA's Adverse Event Reporting System (AERS), 18 cases of skeletal abnormalities were identified in neonates exposed in utero to magnesium sulfate. The average duration of in utero exposure to magnesium sulfate was 9.6 weeks (range 8-12 weeks) with an average total maternal dose of 3700 g. Skeletal abnormalities included osteopenia and multiple fractures of the ribs and long bones. In cases with reported outcomes, fractures were transient and resolved. An epidemiologic study also found an association for an increase in bone abnormalities in neonates with in utero exposure to magnesium sulfate for more than 7 days compared with those exposed < 3 days. The long-term effects of altered laboratory tests and/or radiographic findings suggestive of skeletal abnormalities are unknown. One study in 11 babies reported no radiographic bone abnormalities at 1 and 3 years of age in those that had evidence of bone abnormalities at birth. Other adverse neonatal effects after in utero exposure to magnesium sulfate, particularly when given more than 24 hours before delivery, include hypotonia (reduced reflexes), drowsiness/somnolence, and respiratory depression ; however, such effects appear rare with proper use and monitoring.

Description: Magnesium is the second most abundant intracellular cation. It is has been identified as a cofactor in more than 300 enzymatic reactions involving energy metabolism and protein and nucleic acid synthesis. Several magnesium salts are used clinically. Magnesium chloride, magnesium gluconate, magnesium lactate, and magnesium oxide are oral products used for supplementation in patients with magnesium deficiency due to malnutrition, restricted diet, or magnesium-depleting drugs.

Magnesium sulfate is the most commonly used of the magnesium salts and is administered parenterally (primarily IV). Magnesium sulfate is primarily used for the treatment of hypomagnesemia; however, it is also utilized for other conditions. It is useful in controlling seizures due to acute nephritis in children. Magnesium may also be considered in the treatment of cardiac glycoside-induced arrhythmias. The 2010 ECC/AHA guidelines conclude that IV magnesium during pediatric cardiopulmonary resuscitation has shown effectiveness only for the treatment of patients with hypomagnesemic states or polymorphic ventricular tachycardia (torsade de pointes). Therefore, IV magnesium is not recommended in cardiac arrest except in suspected hypomagnesemic states or for the treatment of torsade de pointes. Other uses for IV magnesium sulfate include refractory status asthmaticus and treatment of persistent pulmonary hypertension of the newborn (PPHN). Parenteral magnesium given by the IM route is FDA-approved for use in pediatric patients as young as neonates. Safety and efficacy of IV administration have not been established; however, the IV route is widely used off-label in pediatric patients as young as neonates.

Elemental Magnesium Content
One (1) gram of the various magnesium salts contain the following amounts of elemental magnesium:
-magnesium chloride: 120 mg (9.8 mEq) elemental magnesium.
-magnesium gluconate: 54 mg (4.5 mEq) elemental magnesium.
-magnesium lactate: 120 mg (10 mEq) elemental magnesium.
-magnesium oxide: 603 mg (50.3 mEq) elemental magnesium.
-magnesium sulfate: 98 mg (8.12 mEq) elemental magnesium.

For nutritional supplementation to maintain adequate intake:
-the recommended dietary allowance (RDA) of magnesium for nutritional supplementation in healthy individuals:
Oral dosage (expressed in elemental magnesium):
Neonates and Infants less than 6 months: 30 mg PO per day based on adequate intake (AI); RDA has not been established.
Infants 6 to 12 months: 75 mg/day PO based on adequate intake (AI); RDA has not been established.
Children 1 to 3 years: 80 mg/day PO is the RDA.
Children 4 to 8 years: 130 mg/day PO is the RDA.
Children and Adolescents 9 to 13 years: 240 mg/day PO is the RDA.
Adolescent females 14 years and older: 360 mg/day PO is the RDA. If pregnant, 400 mg/day PO is recommended.
Adolescent males 14 years and older: 410 mg/day PO is the RDA.
-maintenance requirements to prevent low magnesium and maintain nutritional status in patients receiving total parenteral nutrition (TPN):
Intravenous dosage (magnesium sulfate):
Neonates and Infants: 0.3 to 0.5 mEq/kg/day IV. Individualize dosage according to monitoring.
Children and Adolescents: Recommendations are based on weight; individualize dosage according to monitoring. For weight 50 kg and less, 0.3 to 0.5 mEq/kg/day IV. For weight greater than 50 kg, 10 to 30 mEq/day IV.

For the treatment of hypomagnesemia:
NOTE: Serum magnesium concentrations do not accurately predict cellular magnesium stores. The appropriate route of administration for replacement magnesium is dependent on patient symptoms and the severity of hypomagnesemia. Intravenous magnesium replacement should be used initially for patients with clinically severe conditions, and follow-up oral therapy may also be required to fully replenish body stores.
Intravenous dosage* (magnesium sulfate):
Neonates, Infants, Children, and Adolescents: 25 to 50 mg/kg/dose (Max: 2 g/dose) IV over 30 to 60 minutes. Repeat as necessary based on serum magnesium concentrations.
Intramuscular dosage:
Neonates: 20 to 40 mg/kg/dose (0.1 to 0.2 mL/kg) IM of a 20% solution is recommended in the FDA-approved labeling for pediatric patients; however, IM administration is not commonly utilized in clinical practice. In general, IM administration of drugs in neonates, particularly very low birth weight premature neonates, is not practical due to small muscle mass, and absorption is unreliable due to hemodynamic instability that is relatively common in this population. Doses may be repeated as necessary based on serum magnesium concentrations.
Infants, Children, and Adolescents: 20 to 40 mg/kg/dose (0.1 to 0.2 mL/kg; Max: 2 g/dose) IM of a 20% solution is recommended in the FDA-approved labeling; however, IM administration is not commonly utilized in clinical practice. Doses may be repeated as necessary based on serum magnesium concentrations. The maximum dose recommended in the FDA-approved labeling for older children is 5 g/day for severe hypomagnesemia and 2 g/day for mild or moderate hypomagnesemia.
Oral dosage (magnesium chloride, magnesium gluconate, magnesium lactate, or magnesium oxide):
Infants, Children, and Adolescents: 10 to 40 mg elemental magnesium/kg/day PO in 2 to 4 divided doses is the general dose range. Higher doses (100 mg elemental magnesium/kg/day PO) have been reported ; however, the use of higher doses may be limited by the occurrence of diarrhea. Titrate dose based on serum magnesium concentrations.

For the management of nephritis-associated seizures and/or nephritis-associated hypertension related to acute nephritis:
Intravenous or Intramuscular dosage (magnesium sulfate):
Infants, Children, and Adolescents: 20 to 40 mg/kg/dose (Max: 2 g/dose) IV or IM as needed to control seizures. If giving IM, a 20% solution is recommended. Data for this use in children are lacking.

For the treatment of status asthmaticus*:
Intravenous dosage (magnesium sulfate):
Infants, Children, and Adolescents: 25 to 75 mg/kg/dose (Max: 2 g/dose) IV as a single dose over 15 to 30 minutes. Higher doses (100 mg/kg/dose) have also been reported in children. Asthma guidelines recommend adjunct therapies, such as intravenous magnesium, in patients presenting with life-threatening exacerbations and in those with severe exacerbations that are unresponsive to 1 hour of conventional therapy.
Continuous Intravenous Infusion dosage (magnesium sulfate):
Infants, Children, and Adolescents: 50 mg/kg/dose (Max: 2 g/dose) IV loading dose over 30 minutes, then 25 mg/kg/hour continuous IV infusion, initially, based on limited data from 1 study in 40 children with refractory asthma. Titrate dose based on magnesium serum concentrations (goal 3 to 5 mg/dL), patient response, and tolerability. Continuous infusion dosing has been utilized in order to maintain a stable magnesium concentration vs. peaks and troughs associated with bolus dosing. Guidelines recommend adjunct therapies, such as intravenous magnesium, in patients presenting with life-threatening exacerbations and in those with severe exacerbations that are unresponsive to 1 hour of conventional therapy.
Children and Adolescents weighing 30 kg or more: 50 mg/kg/dose (Max: 2 g/dose) IV loading dose over 30 minutes, then 20 mg/kg/hour (Max: 2 g/hour) continuous IV infusion, initially, based on limited data from 1 study in 40 children with refractory asthma. Titrate dose based on magnesium serum concentrations (goal 3 to 5 mg/dL), patient response, and tolerability. Continuous infusion dosing has been utilized in order to maintain a stable magnesium concentration vs. peaks and troughs associated with bolus dosing. Guidelines recommend adjunct therapies, such as intravenous magnesium, in patients presenting with life-threatening exacerbations and in those with severe exacerbations that are unresponsive to 1 hour of conventional therapy.
Respiratory (Inhalation) dosage (isotonic magnesium sulfate, prepared from injectable formulation):
Children and Adolescents 2 to 17 years: Limited data available. 150 mg/dose inhaled by nebulizer every 20 minutes as needed for 3 doses may be considered as an adjuvant to conventional therapy when mixed with nebulized albuterol and ipratropium in the first hour of treatment for patients with acute severe asthma, particularly those with symptoms lasting less than 6 hours. In a large randomized, placebo-controlled trial (n = 508; age range: 2 to 16 years), those receiving adjuvant nebulized isotonic magnesium sulfate (n = 252) showed a statistically significant, but clinically insignificant improvement in mean Asthma Severity Score at 60 minutes. The greatest clinical response was seen in children with more severe attacks (SaO2 less than 92%) and those with symptoms present for less than 6 hours.

For the treatment of torsade de pointes* (irregular/polymorphic ventricular tachycardia* associated with QT prolongation) or other cardiac arrhythmias associated with documented hypomagnesemia (e.g., ventricular fibrillation* or cardiac glycoside-induced arrhythmias due to either digoxin toxicity*), including use during cardiopulmonary resuscitation* (cardiac arrest*):
Intravenous or Intraosseous dosage (magnesium sulfate):
Neonates, Infants, Children, and Adolescents: 25 to 50 mg/kg/dose (Max: 2 g/dose) IV or IO. Administer by rapid bolus (over several minutes) for pulseless torsades de pointes and over 10 to 20 minutes for hypomagnesemia/torsades de pointes with pulse.

For the treatment of persistent pulmonary hypertension of the newborn* (PPHN) in mechanically ventilated neonates:
Intravenous dosage (magnesium sulfate):
Premature Neonates 29 to 32 weeks gestational age: 200 mg/kg IV loading dose over 20 to 30 minutes followed by a continuous infusion of 20 to 50 mg/kg/hour IV was used in a small prospective, non-randomized trial of 7 premature neonates (birth weight 1,232 to 2,346 g). Serum magnesium concentrations ranged from 2.75 to 6.63 mmol/L during magnesium therapy. Other reports that include neonates born before 33 weeks gestation as well as neonates of older gestational ages reported loading doses of 200 mg/kg IV followed by infusions of 20 to 150 mg/kg/hour titrated to maintain blood magnesium concentrations in the general range of 3 to 5.5 mmol/L. In addition to respiratory status, carefully monitor serum electrolytes, renal function, heart rate, and blood pressure during magnesium therapy.
Premature Neonates 33 weeks gestational age and older and Term Neonates: 200 mg/kg IV loading dose over 20 to 30 minutes followed by a continuous infusion of 20 to 150 mg/kg/hour IV titrated to maintain blood magnesium concentrations within the general range of 3 to 5.5 mmol/L (target range varies among studies) has been effective in small studies. One small randomized study reported targeting a higher serum magnesium range of 5 to 7 mmol/L. In addition to respiratory status, carefully monitor serum electrolytes, renal function, heart rate, and blood pressure during magnesium therapy.

For the treatment of muscle spasm* and dysautonomia* due to tetanus*:
Intravenous dosage (magnesium sulfate):
Neonates: 50 mg/kg IV once, then 30 to 50 mg/kg/hour continuous IV infusion until spasm control and to maintain serum magnesium concentrations of 1 to 2.5 mmol/L. Monitor patellar reflex and decrease dose if areflexia occurs.
Infants, Children, and Adolescents: 100 mg/kg IV once, then 40 mg/kg/hour continuous IV infusion; may titrate by 5 mg/kg/hour every 6 hours until spasm control and to maintain serum magnesium concentrations of 2.5 to 5 mmol/L. Max: 100 mg/kg/hour. Monitor patellar reflex and decrease dose if areflexia occurs. Lower infusion rates of 4 to 17 mg/kg/hour have also been used successfully.

Therapeutic Drug Monitoring:
-Normal serum magnesium concentrations range from 1.5-2.1 mEq/L in children and 1.5-2.2 mEq/L in neonates and infants; ranges may vary depending upon laboratory standards.
-All neonates with a history of prolonged in utero exposure to parenteral magnesium sulfate should be monitored carefully for hypocalcemia and bone abnormalities. Continuous administration of magnesium sulfate as a tocolytic during pregnancy beyond 5-7 days has resulted in bone abnormalities, including skeletal demineralization, osteopenia, and neonatal fracture.
-Other: deep tendon reflexes, respirations, and urinary output.

Maximum Dosage Limits:
Dosage must be individualized according to the indication, patient's serum magnesium concentrations, and clinical response.
-Neonates
40 mg/kg/dose IM; safety and efficacy of IV use have not been established; however, maximum doses of 50 mg/kg/dose IV for torsades de pointes and hypomagnesemia and 200 mg/kg/dose IV for persistent pulmonary hypertension of the newborn (PPHN) have been used off-label; up to 100 mg elemental magnesium/kg/day PO has been used for deficiency.
-Infants
40 mg/kg/dose IM; safety and efficacy of IV magnesium have not been established; however, maximum doses of 50 mg/kg/dose IV for torsades de pointes and hypomagnesemia and 100 mg/kg/dose IV for status asthmaticus have been used off-label; up to 100 mg elemental magnesium/kg/day PO has been used for deficiency.
-Children
40 mg/kg/dose IM; safety and efficacy of IV magnesium have not been established; however, maximum doses of 50 mg/kg/dose (Max: 2 g/dose) IV for torsades de pointes and hypomagnesemia and 100 mg/kg/dose IV for status asthmaticus have been used off-label; up to 100 mg elemental magnesium/kg/day PO has been used for deficiency.
-Adolescents
40 mg/kg/dose IM; safety and efficacy of IV magnesium have not been established; however, maximum doses of 50 mg/kg/dose (Max: 2 g/dose) IV for torsades de pointes and hypomagnesemia and 100 mg/kg/dose IV for status asthmaticus have been used off-label; up to 100 mg elemental magnesium/kg/day PO has been used for deficiency.

Patients with Hepatic Impairment Dosing
Magnesium is eliminated entirely in the kidneys; no dosage adjustment is necessary in patients with hepatic impairment.

Patients with Renal Impairment Dosing
Magnesium is eliminated entirely in the kidneys. Dosage should be modified depending on clinical response and degree of renal impairment, but no quantitative recommendations are available.

Intermittent hemodialysis
Dosage should be modified depending on clinical response, degree of renal impairment, and frequency of hemodialysis; no quantitative recommendations are available.

*non-FDA-approved indication

Monograph content under development

Mechanism of Action: Magnesium is a cofactor to all enzymes involved in phosphate transfer reactions that use ATP and other nucleotides as substrates. Magnesium ions are a cofactor for the normal function of the ATP-dependent sodium-potassium "pump" found in muscle membranes. Without magnesium, the efficiency of this pump is compromised. It is believed that hypomagnesemia is an important aspect of hypokalemia. Drugs that cause severe hypokalemia, such as cisplatin, amphotericin B, and loop diuretics, also cause hypomagnesemia. Correction of hypomagnesemia facilitates the treatment of hypokalemia by improving the pump's ability to distribute potassium into the intracellular space. This mechanism also may explain the effectiveness of intravenous magnesium sulfate in treating cardiac glycoside-induced arrhythmias, although magnesium may exert therapeutic effects independently of a direct action on the sodium-potassium pump. It is postulated that magnesium is effective via its ability to decrease calcium uptake and decrease potassium efflux at the myocardial cell membrane. Conversely, calcium is a direct antagonist of magnesium.

The role of magnesium for the treatment of severe asthma exacerbations is not clearly defined. Magnesium decreases the uptake of calcium by bronchial smooth muscle cells, which results in bronchodilation. Magnesium may also inhibit mast cell degranulation, thus decreasing inflammatory mediators such as histamine, thromboxanes, and leukotrienes. Additionally, magnesium inhibits the release of acetylcholine from motor nerve terminals and depresses the excitability of muscle fibre membranes. Magnesium also stimulates nitric oxide and prostacyclin synthesis, which may decrease asthma severity.

High magnesium serum concentrations result in vasodilation, muscle relaxation, and sedation. Some studies have shown that magnesium can prevent and reduce hypoxia-induced pulmonary hypertension, leading to its use in the treatment of persistent pulmonary hypertension of the newborn (PPHN).

As an anticonvulsant, magnesium sulfate depresses the CNS and blocks peripheral neuromuscular transmission. Depression in the CNS may be achieved through inhibition of acetylcholine release by motor nerve impulses. Magnesium is a peripheral vasodilator and an inhibitor of platelet function. Large doses can lower blood pressure and cause CNS depression.

Pharmacokinetics: Magnesium sulfate is administered parenterally; magnesium chloride, gluconate, lactate, and oxide are administered orally. Magnesium is distributed throughout the body. Approximately 99% of the total body magnesium is intracellular (bone, 85%; soft tissue and liver, 14%). Only 1% of the total body magnesium is present in the blood. Magnesium is 30% bound to albumin. Normal serum concentrations range from 1.5 to 2.1 mEq/L in children and 1.5 to 2.2 mEq/L in neonates and infants. As an anticonvulsant, effective serum magnesium concentrations have been reported to range from 2.5 to 7.5 mEq/L. Magnesium is not metabolized. Elimination occurs renally, but the rate of excretion varies. Most of the filtered magnesium (approximately 95%) is reabsorbed in the nephron (60% to 70% in the thick ascending limb of the loop of Henle, 15% to 25% in the proximal tubule, and 5% to 10% in the distal convoluted tubule).

Affected cytochrome P450 isoenzymes: none


-Route-Specific Pharmacokinetics
Oral Route
Approximately 34% to 40% of oral magnesium salts are absorbed systemically with a normal diet; however, absorption can increase to 76% in those receiving only 2 mEq/day of magnesium.

Intravenous Route
Anticonvulsant Action
After IV administration, the onset of action is immediate and the duration of effect is approximately 30 minutes.

Intramuscular Route
Anticonvulsant Action
After IM administration, the onset of action occurs in approximately 1 hour and the duration of effect is 3 to 4 hours.