Magnesium
CLASS
- electrolyte (second most abundant cation in intracellular fluid, after potassium)
MECHANISM OF ACTION
- depresses neuronal activation
- essential cofactor in >300 enzyme systems and essential for the production of ATP, DNA, RNA & protein function.
PHARMACEUTICS
- sulphate or chloride
- clear, colourless
- 10 mmol in 10mL
DOSE
- 5mmol bolus -> 20mmol over 60 min
INDICATIONS
- Mg deficiency (if develops in ICU treat as associated with increased mortality and prolonged LOS)
- arrhythmias (post ischaemia/cardiac surgery)
- post MI
- asthma/severe bronchospasm
- pre-eclampsia/eclampsia
- SAH management
- tocolytic
- pheochromocytoma surgery
- hypokalaemia (will need to treat hypomagnesaemia in this context)
ADVERSE EFFECTS
- nausea
- flushing
- CNS depression
- coma
- heart block
- respiratory weakness
- toxicity -> IV calcium
PHARMACOKINETICS
- Absorption – IV (via CVL)
- Distribution – widely distributed, 30% protein bound
- Metabolism – nil
- Elimination – filled by kidneys
EVIDENCE
- see Mg2+ document in Electrolytes
Eclampsia
- standard of care
- halves rate of progression from pre -> eclampsia
- drug of choice in treating eclamptic seizures – more effective than phenytoin or benziodiazepines (MAGPIE trial 2002, Cochrane review, 2003)
- dose: 4g over 5min -> 1g/hr (aim for a level of 2-4mmol/L)
Arrhythmias
- likely to be effective in a subgroup of patients with total body Mg deficiency, however this group is hard to diagnose.
- post cardiac surgery -> meta-analyses have shown that IV Mg decreases occurrence of post of AF and ventricular arrhythmias
- not yet currently endorsed by the AHA/European Heart Association
- may be as effective as amiodarone in treating rapid AF (Critical Care Med, 1995)
- recommended for treatment of Torsades des Pointes, but no RCT on this.
- effective in digitalis induced arrhythmias
Post Myocardial Infarction
- controversial (not widely accepted)
- conflicting evidence
- early trials (LIMIT2) showed a mortality benefit
- later trials (ISIS4, MAGIC) were unable to reproduce findings
Asthma/Bronchospasm
- improves FEV1 and PEFR in some patients (those at severe end of spectrum)
- no evidence to support improvement in mortality
- of benefit in selected patients ?maybe more effective in paediatric patients
- dose = 5-10mmoL over 20 min
- Cochrane review, 2000
- more trials needed
SAH Management
- rat models demonstrate effectiveness of IV Mg in reversing induced vaspasm (Stroke, 1991)
References and Links
CCC Pharmacology Series
Respiratory: Bosentan, Delivery of B2 Agonists in Intubated Patients, Nitric Oxide, Oxygen, Prostacyclin, Sildenafil
Cardiovascular: Adenosine, Adrenaline (Epinephrine), Amiodarone, Classification of Vasoactive drugs, Clevidipine, Digoxin, Dobutamine, Dopamine, Levosimendan, Levosimendan vs Dobutamine, Milrinone, Noradrenaline, Phenylephrine, Sodium Nitroprusside (SNiP), Sotalol, Vasopressin
Neurological: Dexmedetomidine, Ketamine, Levetiracetam, Lignocaine, Lithium, Midazolam, Physostigmine, Propofol, Sodium Valproate, Sugammadex, Thiopentone
Endocrine: Desmopressin, Glucagon Therapy, Medications and Thyroid Function
Gastrointestinal: Octreotide, Omeprazole, Ranitidine, Sucralfate, Terlipressin
Genitourinary: Furosemide, Mannitol, Spironolactone
Haematological: Activated Protein C, Alteplase, Aprotinin, Aspirin, Clopidogrel, Dipyridamole, DOACs, Factor VIIa, Heparin, LMW Heparin, Protamine, Prothrombinex, Tenecteplase, Tirofiban, Tranexamic Acid (TXA), Warfarin
Antimicrobial: Antimicrobial Dosing and Kill Characteristics, Benzylpenicillin, Ceftriaxone, Ciprofloxacin, Co-trimoxazole / Bactrim, Fluconazole, Gentamicin, Imipenem, Linezolid, Meropenem, Piperacillin-Tazobactam, Rifampicin, Vancomycin
Analgesic: Alfentanil, Celecoxib, COX II Inhibitors, Ketamine, Lignocaine, Morphine, NSAIDs, Opioids, Paracetamol (Acetaminophen), Paracetamol in Critical Illness, Tramadol
Miscellaneous: Activated Charcoal, Adverse Drug Reactions, Alkali Therapies, Drug Absorption in Critical Illness, Drug Infusion Doses, Epidural Complications, Epidural vs Opioids in Rib Fractures, Magnesium, Methylene Blue, Pharmacology and Critical Illness, PK and Obesity, PK and ECMO, Sodium Bicarbonate Use, Statins in Critical Illness, Therapeutic Drug Monitoring, Weights in Pharmacology
Toxicology: Digibind, Flumazenil, Glucagon Therapy, Intralipid, N-Acetylcysteine, Naloxone, Propofol Infusion Syndrome
Journal articles
- Wu J, Carter A. Abnormal Laboratory Results: Magnesium: the forgotten electrolyte. Aust Prescr. 30(4):102-105. 2007. [article]
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
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