pralidoxime
cholinesterase reactivator· Brands: Protopam, ContrathionIMIVPO
Mechanism of action
Pralidoxime reactivates acetylcholinesterase that has been phosphorylated by organophosphate compounds. It binds to the phosphate moiety and cleaves the enzyme-phosphate bond, restoring the enzyme's catalytic activity. It also has direct anticholinergic effects, which may contribute to its therapeutic action.
Pharmacokinetics
Pralidoxime is administered intravenously or intramuscularly, with rapid distribution throughout the body. It is not appreciably metabolised and is excreted unchanged in the urine, with an elimination half-life of approximately 1 to 2 hours.
Indications & dosing
Organophosphate insecticide poisoning (moderate to severe)
Administer with atropine; repeat doses based on clinical response.
- adult · IV/IM: 1000–2000 mg every 1-2 h · Administer with atropine; repeat doses based on clinical response.
Organophosphate insecticide poisoning (moderate to severe)
Administer with atropine; repeat doses based on clinical response.
- pediatric · IV/IM: 20–50 mg/kg every 1-2 h · Administer with atropine; repeat doses based on clinical response.
Nerve agent poisoning (e.g., sarin, VX)
Given in conjunction with atropine in chemical exposure settings.
- adult · IV/IM: 1000–2000 mg repeat every 1-2 h · Given in conjunction with atropine in chemical exposure settings.
Contraindications & precautions
- Known hypersensitivity to pralidoxime or any component · Do not administer in patients with a history of allergic reaction to pralidoxime.
- Myasthenia gravis · Pralidoxime may worsen muscle weakness in myasthenia gravis. Use only if the benefits outweigh the risks.
- Carbamate poisoning · Pralidoxime is ineffective in carbamate poisoning and may theoretically worsen the condition. Avoid unless organophosphate poisoning is confirmed.
- Administer concurrently with atropine, as atropine is essential for controlling muscarinic effects.
- Monitor heart rate, blood pressure, respiratory status, and neurological status during treatment.
- Use caution in patients with renal impairment; consider dose reduction as pralidoxime is renally excreted.
- Use caution in patients with myasthenia gravis, as pralidoxime may exacerbate weakness.
- Avoid use in carbamate poisoning unless organophosphate poisoning is confirmed.
Adverse effects
- Injection site pain
- Tachycardia
- Hypertension
- Dizziness
- Blurred vision
- Nausea and vomiting
- Seizuresserious
- Cardiac arrhythmiasserious
- Anaphylaxisserious
Renal & hepatic adjustment
- eGFR 0+: Consider reducing dose or extending dosing interval in renal impairment; pralidoxime is mainly excreted unchanged in urine.
Monitoring, pregnancy & toxicity
- Clinical response (muscle strength, respiratory function) · Continuously during treatment
- Plasma cholinesterase activity · Before and after treatment
- Vital signs (BP, heart rate) · During and after infusion
- Cardiac rhythm · Continuous monitoring if significant toxicity
- Pregnancy: Use is appropriate in life-threatening organophosphate poisoning despite potential risks; benefits outweigh risks in emergency.
- Toxicity: Hypertension and tachycardia · Monitor vital signs; reduce infusion rate or stop if severe.
- Toxicity: Neuromuscular blockade (in high doses) · Stop infusion; provide supportive care, mechanical ventilation if needed.
- Toxicity: Dizziness, blurred vision · Symptomatic treatment; may resolve with dose reduction.
Clinical notes
Pralidoxime is used in the treatment of organophosphate poisoning, often in combination with atropine. It is most effective when given early, before the enzyme undergoes 'ageing'. Adverse effects include hypertension, tachycardia, dizziness, and pain at the injection site. The dose depends on the severity of poisoning and patient weight, and local protocols should be followed.
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BNF; local formulary