Magnesium Sulfate in Organophosphate (OP) Poisoning

Proposed mechanism

• OP compounds cause excessive acetylcholine accumulation (acetylcholinesterase inhibition) → overstimulation of muscarinic and nicotinic receptors, plus excess presynaptic ACh release which is partly Ca2+-channel dependent.
• Magnesium acts as a physiological calcium antagonist: it blocks voltage-gated calcium channels at the presynaptic nerve terminal, reducing acetylcholine release, and also has NMDA-receptor antagonism that may help with OP-induced seizures/agitation.
• This is the same rationale historically proposed for calcium channel blockers, though no trial evidence supports the latter (De Santi et al. 2025 meta-analysis, PMID 40792609).

Reported dosing (as cited in sources)

• Goldman-Cecil Medicine cites a regimen of magnesium sulfate 4 g IV over 30 minutes, alongside titrated atropine (Goldman-Cecil Medicine, p. 4351-4353).
• Trial protocols in the literature generally use IV MgSO4 boluses/infusions in the gram range, similar to eclampsia dosing, with careful monitoring given the risk of hypotension and respiratory depression at high doses.

Evidence base

• Mortality: RR 0.37 (95% CI 0.22-0.64) favoring MgSO4 as adjunct — a substantial reduction.
• Atropine requirement: significantly reduced (mean difference -23.27 mg/day, 95% CI -36.57 to -9.97).
• No significant difference in hospital length of stay or need for mechanical ventilation.
• Safety: generally favorable; one study reported transient hypotension with higher infusion rates.
• Authors' caution: studies were small and heterogeneous — "larger, well-designed randomized controlled trials are needed" before MgSO4 can be recommended as standard care.

Practical takeaway

• MgSO4 can be considered as an adjunct to standard atropine/pralidoxime therapy in acute OP insecticide poisoning, especially where local protocols or clinical toxicology consultation support it - it may lower mortality and atropine needs with an acceptable safety profile.
• It should not replace atropine, oxime therapy, airway/respiratory support, or decontamination.
• Monitor for hypotension and hypermagnesemia (reflexes, respiratory rate) during infusion, especially in renal impairment.
• Because evidence still comes from a modest pool of RCTs, most emergency medicine references (e.g., Tintinalli's) do not yet endorse it as routine practice - use is best guided by local toxicology/poison-control protocols.