Electrolyte / antiarrhythmic / anticonvulsant

Magnesium sulfate

Adult dose

Dose: Hypomagnesaemia: 5–10mmol IV. Severe asthma: 1.2–2g (5–8mmol) IV over 20 min. Eclampsia/severe pre-eclampsia: loading 4g IV over 5–15 min, then 1g/h infusion for 24h. Torsades: 2g IV over 1–2 min

Route: IV/IM

Frequency: per indication

Clinical pearls

Eclampsia: continuous infusion + monitor reflexes/RR/UO; calcium gluconate 10% 10mL is the antidote
Severe asthma 2nd-line; torsades in normo-/hyperkalaemia

Contraindications

Heart block
Severe renal impairment (caution)
Myasthenia gravis

Side effects

Hypotension
Bradycardia
Loss of patellar reflex
Respiratory depression at high levels (>4 mmol/L)
Hypermagnesaemia

Interactions

Neuromuscular blockers (potentiation)
Calcium-channel blockers
Aminoglycosides
Digoxin

Monitoring

Reflexes
RR
Urine output
Serum Mg in renal impairment
ECG

Reference: BNF; NICE NG133; UK Resus Council; BTS/SIGN asthma; https://bnf.nice.org.uk/drugs/magnesium-sulfate/. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways