Pralidoxime is a cholinesterase reactivator used as an antidote in the treatment of poisoning by organophosphorus compounds (pesticides and nerve agents). It is a quaternary ammonium oxime that reactivates acetylcholinesterase (AChE) inhibited by organophosphates by removing the phosphoryl group from the enzyme's active site. It is most effective when administered within 24-36 hours of exposure, before the phosphorylated enzyme undergoes 'aging' (irreversible dealkylation). In the Indian context, it is a critical component of hospital emergency protocols, especially in agricultural regions with high incidence of pesticide poisoning.
Adult: Initial: 1-2 g (30-40 mg/kg) IV, administered slowly over 15-30 minutes. Alternatively, can be given as an IV infusion in 100 ml normal saline over 15-30 min. Maintenance: Either repeat the initial dose every 4-6 hours if symptoms recur, OR administer a continuous IV infusion of 500 mg/hour (approx. 8-10 mg/kg/hour). Total daily dose should not exceed 12 g. IM route can be used if IV access is unavailable.
Note: For 25mg/ml solution: Dilute the required dose (e.g., 2g = 80ml) in 100-150 ml of 0.9% Sodium Chloride Injection. Administer IV over 15-30 minutes. Rapid IV injection can cause tachycardia, laryngospasm, muscle rigidity. IM injection can be given undiluted into a large muscle mass. Incompatible with alkaline solutions. Protect from light.
Organophosphorus compounds (OPs) phosphorylate the serine hydroxyl group at the active site of acetylcholinesterase (AChE), leading to irreversible inhibition and accumulation of acetylcholine. Pralidoxime acts as a nucleophile. Its oxime group (-CH=NOH) attacks the phosphorus atom of the phosphorylated AChE, forming an oxime-phosphonate complex. This complex then splits, regenerating the active enzyme and releasing the phosphorylated oxime.
Pregnancy: Category C (US FDA). No well-controlled studies in pregnant women. Use only if clearly needed and potential benefit justifies potential risk to the fetus. In life-threatening maternal poisoning, treatment should not be withheld.
Driving: Causes dizziness, drowsiness, and blurred vision. Patients should be warned not to drive or operate machinery until these effects have resolved, which may be several hours after the last dose.
| Atropine | Synergistic therapeutic effect. Atropine MUST be given first to block muscarinic effects before pralidoxime is administered. | Major |
| Barbiturates (e.g., Phenobarbital) | Pralidoxime may potentiate the effects of barbiturates. Use with caution. | Moderate |
| Aminophylline, Theophylline | Increased risk of seizures. Monitor closely. | Moderate |
| Succinylcholine, other neuromuscular blockers | Effects may be prolonged in organophosphate poisoning. Pralidoxime may reverse blockade. | Major |
| Reserpine | Theoretical risk of increased hypertension. Avoid concomitant use. | Moderate |
Same composition (Pralidoxime (25mg/ml)), different brands: