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Hypomagnesaemia

  • See also

    Electrolyte abnormalities
    Hypermagnesaemia

    Key points

    1. Oral/enteral is the preferred route of magnesium administration
    2. Consider oral magnesium replacement in asymptomatic children with mild hypomagnesaemia and no gastrointestinal intolerance present eg diarrhoea, nausea, vomiting
    3. Intravenous magnesium replacement is the preferred route in the setting of symptomatic hypomagnesaemia, significant gastrointestinal intolerance
    4. Seek specialist advice for symptomatic children with hypomagnesaemia

    Background

    • Serum magnesium levels may not reflect total body stores
    • Less than 1% of total body magnesium stores are in extracellular fluid
    • Earlier changes may be identified in urine levels in the context of normal renal function, using 24-hour urinary magnesium excretion
    • The clinical context of the child is required to interpret the significance of a low magnesium level eg post-surgical cardiac conditions, where clinical target may be the upper end of normal range to avoid arrhythmia

    Causes of hypomagnesaemia

      Gastrointestinal

    Increased renal excretion

    Other

    Reduced intake


    Reduced absorption

    • Malabsorption
    • Short bowel syndrome

    Increased losses

    • Diarrhoea
    • Laxative abuse
    • Excessive gastric suctioning or vomiting

    Drug-induced

    • Loop diuretics, thiazides
    • Cisplatin
    • Tacrolimus, ciclosporin
    • Proton pump inhibitors [chronic use]
    • Aminoglycosides

    Other

    • Renal tubular acidosis
    • Diuretic phase of acute tubular necrosis
    • Hypercalcemic states
    • Hyperaldosteronism

    Intracellular redistribution

    • diabetic ketoacidosis
    • hyperthyroidism

    Miscellaneous

    • burns
    • cardiopulmonary bypass

    Assessment

    Identify underlying cause and correct where possible

    Assess for signs/symptoms of hypomagnesaemia

    • Neuromuscular: muscle tremors, fasciculations, hyperreflexia, paraesthesia, muscle weakness, myalgia
    • Cardiac: arrhythmias and ECG changes (PR/QT prolongation)
    • Metabolic: hypokalaemia, hypocalcaemia
    • Central nervous system: nystagmus, seizures, depression, agitation, confusion, irritability

    Management

    Investigations

    Serum magnesium levels should be monitored with frequency depending on the degree of abnormality and whether the child is symptomatic

    Treatment

    Consider oral magnesium replacement in asymptomatic children with mild hypomagnesaemia, unless significant gastrointestinal intolerance (eg diarrhoea) which oral magnesium will exacerbate:

    • 2.5 - 5 mg/kg (0.1 - 0.2 mmol/kg) 3 times daily orally
    • Increase to 10 - 20 mg/kg (0.4 - 0.8 mmol/kg) up to 4 times daily orally if required
    • Tolerance is better with smaller more frequent dosing

    Medication Form for oral/enteral magnesium

    Preparation

    Magnesium*
    content

    Magnesium complex solution

    2.1 mmol per mL
    (50 mg/mL)

    Magnesium aspartate tablet (MagMin@; Mag-Sup@)

    1.55 mmol per tablet
    (37.4 mg per tablet)

    Cenovis@ Magnesium tablets
    (also contains 6 mg manganese and 49.36 mg pyridoxine per tablet)

    13.5 mmol per tablet
    (325 mg per tablet)

    Children with severe symptoms (eg tetany, arrythmia, seizures) should be treated with intravenous magnesium

    • Seek specialist advice for IV magnesium replacement
    • IV magnesium 0.1 - 0.2 mmol/kg up to 0.4 mmol/kg (max dose 8 mmol)
      • Administer over 2-4 hours, (reduces risk of adverse effects, also improves cellular uptake of administered dose)
      • In children with severe symptoms, can be given over shorter period of time
    • Please refer to local guidelines for more detailed administration information

    Medication Form for intravenous magnesium

    Preparation
    (Concentrated magnesium ampoules)

    Magnesium*
    content

    Notes

    DBL Magnesium Sulfate concentrated injection 49.3%

    2 mmol/mL
    (493 mg/mL)

     

    Dilute before use

    Magnesium Sulfate Heptahydrate concentrated injection 50%

    2 mmol/mL
    (500 mg/mL)

    Consider consultation with local paediatric team when

    The child is symptomatic, or there is a severe abnormality

    Consider consultation with the clinical nutrition, gastroenterology team or local dietitian when

    • Hypomagnesaemia in a child on parenteral nutrition
    • Hypomagnesaemia in a child with refeeding syndrome

    Consider consultation with renal team when

    • Unexplained hypomagnesaemia
    • Hypomagnesaemia with associated moderate-severe renal impairment (risk of hypermagnesemia with replacement)

    Consider transfer when

    The child is symptomatic or requires close monitoring not available in your centre

    For emergency advice and paediatric or neonatal ICU transfers, see Retrieval Services

    Consider discharge when

    • The child is clinically stable with an appropriate management plan in place
    • Any acute or chronic abnormality has resolved

    Last Updated November 2021

  • Reference List

    1. Australian Medicines Handbook Children’s Dosing Companion.  2020.  Australian Medicines Handbook Pty Ltd. Adelaide.
    2. Canada TW, et al.  ASPEN Fluids, Electrolytes, and Acid-Base Disorders Handbook. 2015. American Society for Parenteral and Enteral Nutrition. U.S.A.
    3. Paediatric Injectable Guidelines Online.  Magnesium sulfate.   Retrieved from https://pig.rch.org.au/monographs/magnesium-sulphate/ (viewed 14 July 2021).
    4. Rees, L, et al. Paediatric Nephrology (Oxford Specialist Handbooks in Paediatrics), 3rd Edition 2019