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Antidotes & Toxicology Pregnancy: Use if benefit outweighs risk — organophosphate poisoning is life-threatening; animal data show teratogenicity at high doses

Pralidoxime

Brand names: P2S, Pralidoxime Mesylate

Adult dose

Dose: 30 mg/kg loading over 30 minutes, then 8–10 mg/kg/hour infusion
Route: IV
Frequency: Continuous infusion after loading
Max: 12 g/day
Reconstitute with water for injection; give with atropine — pralidoxime does NOT replace atropine. Give as soon as possible — less effective after 24–48 hours (aging of enzyme)

Paediatric dose

Dose: 20–40 mg/kg loading mg/kg
Route: IV
Frequency: Then 10–20 mg/kg/hour
Max: 12 g/day
Seek specialist opinion; WHO guidelines recommend pralidoxime in all moderate-severe organophosphate poisoning

Dose adjustments

Renal

Reduce maintenance dose in renal impairment — pralidoxime is renally excreted; seek specialist advice

Hepatic

No specific adjustment

Paediatric weight-based calculator

Seek specialist opinion; WHO guidelines recommend pralidoxime in all moderate-severe organophosphate poisoning

Clinical pearls

  • Mechanism: nucleophilic reactivation of phosphorylated acetylcholinesterase — breaks the organophosphate-enzyme bond and regenerates functional AChE, which then metabolises accumulated acetylcholine
  • Time-critical: AGING — the organophosphate-AChE bond undergoes irreversible dealkylation (aging); pralidoxime is INEFFECTIVE after aging (24–48h depending on compound); give as early as possible
  • Works on nicotinic effects (muscle weakness, fasciculations) — atropine works on muscarinic effects (SLUDGE: salivation, lacrimation, urination, defecation, GI upset, emesis); BOTH are required together
  • Nerve agents (VX, sarin, tabun, soman): pralidoxime is part of the military/CBRN antidote kit alongside atropine; soman has very rapid aging (minutes) — less effective
  • MHRA: pralidoxime is licensed for organophosphate poisoning in the UK; supplies maintained by NHS stockpile — contact NPIS (0344 892 0111) for guidance on dose and logistics
  • Do NOT give pralidoxime in carbamate poisoning (aldicarb, carbofuran) — carbamate-AChE bond undergoes spontaneous hydrolysis and pralidoxime may paradoxically worsen the condition

Contraindications

  • Carbamate pesticide poisoning — pralidoxime is NOT effective and may worsen carbamate poisoning
  • Morphine, theophylline, and succinylcholine — relative contraindications in organophosphate poisoning (increase cholinergic effects)

Side effects

  • Hypertension and tachycardia (especially with rapid IV bolus — NEVER give rapidly)
  • Muscle rigidity
  • Headache, dizziness
  • Nausea
  • Laryngospasm with rapid infusion

Interactions

  • Atropine (synergistic — pralidoxime enhances atropine effect; atropine dose may need reduction after pralidoxime given)
  • Do not mix with alkaline solutions (pralidoxime is unstable above pH 7)

Monitoring

  • Cholinergic signs: miosis, bradycardia, bronchospasm, excessive secretions
  • Muscle power and fasciculations (nicotinic effects)
  • Atropine requirement (reduces as pralidoxime takes effect)
  • Plasma cholinesterase if available — low level confirms diagnosis
  • Blood pressure (hypertension risk with rapid infusion)

Reference: BNFc; BNF 90; NPIS Toxbase; WHO Guidelines for Organophosphate Poisoning; Lancet 2009;374(9694):992-1000. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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