Magnesium Sulphate

Registered South African indications:

• Hypomagnesaemia

Contraindications

• Hypersensitivity to the active ingredient or any of its excipients
• Severe renal impairment, except in pre-eclampsia/eclampsia

Cautions

• Pregnancy
• Breastfeeding
• Mild to moderate renal impairment
• Hepatic impairment
• Hepatic coma if there is a risk of renal failure
• Myasthenia gravis

Forms avail. in SA and covered in this monograph: inj

Eclampsia
- Where no infusion pump is available

Loading dose

• IV: 4g, as an infusion given over 20mins

Maintenance

• IM: 5g, 4hrly; Administered at different sites, until 24hrs after delivery or following the last convulsion
  Refer to eclampsia: STG, 2019

Eclampsia
- In high-care setting

• IV: Loading dose: 4g, as an infusion given over 20mins; Maintenance; 1g/hr, until 24hrs after delivery or following the last convulsion
  Refer to eclampsia: STG, 2019

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Dilute in 200ml 0.9% normal saline

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Stop magnesium sulphate if knee reflexes become absent, urine output <100ml/4hrs or respiratory rate <16 breaths per minute

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Eclampsia
- Recurrent eclamptic seizures despite loading dose administration

• IV: 2g, given over 10mins
  Refer to eclampsia: STG, 2019

Acute pancreatitis
- If serum magnesium <0.5 mmol/L

• IV: 25-50mmol, over 12-24hrs
  Refer to pancreatitis, acute: STG, Adult 2019

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1ml magnesium sulfate 50% = 2 mmol magnesium

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Anaesthetic related acute hypertension (Additional agent required)
- To obtund the hypertensive response to intubation 

• IV: 30mg/kg

Acute asthma
- In patients with a poor response

• IV: 2g, as a single dose infused over 20mins
  Refer to asthma, acute: STG, Adult 2019

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Dilute in 200ml 0.9% normal saline 

Paed. forms avail. in SA and covered in this monograph: inj

Hypomagnesaemia in malnutrition

• Oral (inj): 0.2ml/kg, dly; Treatment duration: ≥2 weeks (50% sol.)

Hypomagnesaemia
- Serum magnesium < 0.6mmol/L

Newborn

• IV: 0.2ml/kg, as a single dose (50% sol.)

Hypomagnesaemia in maintenance anticonvulsant therapy
- Serum magnesium < 0.6mmol/L

• IV: 0.25ml/kg administered over 3 minutes, as a single dose (50% sol)

Hypomagnesaemia with hypocalcaemia

Neonates

• IV: 0.25ml/kg (50% sol)

Children

• IV/IM: 0.2ml/kg, 12–24hrly (50% sol)

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Correct hypomagnesaemia before administering calcium gluconate

Pregnancy

• Caution
• Safety in human pregnancy has not been established, however, in the medical emergency of a patient having eclampsia, magnesium sulfate can be administered to relieve this condition, which may be life-threatening to both mother and baby
• Magnesium crosses the placenta. When used in pregnant women, foetal heart rate should be monitored and use within 2 hours of delivery should be avoided

Breastfeeding

• Caution
• Magnesium is excreted in breast milk. Safety in breastfeeding has not been established. Only use when considered essential

Renal Impairment

• Mild to moderate: Caution; dose adjustment recommended
  Reduce dose by 50%
• Pre-eclampsia/eclampsia: Severe: Caution; dose adjustment recommended
  Max: 20g/48hrs
• Hypomagnesemia: Severe: Contraindicated

Hepatic Impairment

• Caution; no dose adjustment recommended 

Elderly

• No dose adjustment recommended

Porphyria Information

• Not porphyrinogenic (NP)

Drugs in Sport

• Permitted - No warnings

Central Nervous System Disorders

• Drowsiness 
• Confusion  
• Coma
• Slurred speech  

Cardiovascular Disorders

• Flushing 
• Hypotension 
• Arrhythmias 
• Cardiac arrest
• ECG changes  
• Bradycardia 

Respiratory Disorders

• Respiratory depression

Gastrointestinal Disorders

• Nausea and vomiting

Endocrine and Metabolic Disorders

• Hypocalcaemia 
• Electrolyte abnormalities 
• Fluid abnormalities 
• Thirst 

Musculoskeletal Disorders

• Loss of tendon reflexes 
• Muscle weakness 

Immune, Blood and Lymphatic System Disorders 

• Hypersensitivity reactions 

Sensory Disorders

• Double vision

• Digitalis glycosides
• Barbiturates
• Opioids 
• Hypnotics 
• Non-depolarising muscle relaxants 
• Calcium channel blockers 
• Aminoglycosides

• Serum magnesium
• Serum calcium

Specific cases may require

• ECG
• Vital signs
• Renal function

Magnesium is the second most abundant cation in intracellular fluid and is an essential body electrolyte. It is a factor in a number of enzyme systems, and is involved in neurochemical transmission and muscular excitability. Parenterally administered magnesium sulphate exerts a depressant effect on the central nervous system and acts peripherally to produce vasodilation. It causes direct inhibition of action potentials in myometrial muscle cells. Excitation and contraction are uncoupled, which decreases the frequency and force of contractions.

Magnesium Sulphate is available in several formulations. Please note the list below gives examples of products which are available and is not necessarily comprehensive. The listing of a product does not constitute endorsement of the product by EMGuidance; likewise, failure to list a product does not imply that EMGuidance disapproves of the product. This information is put together on the basis of the National Government's Medicines Price Registry at the time of publication.

Injection (per 2ml) 1g

• Sabax Magnesium Sulphate (Adcock)