Organophosphorus Poisoning MCQs

Mild poisoning usually occurs when cholinesterase activity is 20 to 50% of normal. Moderate poisoning occurs when activity is 10 to 20% of normal. Severe poisoning when activity is less than 10% normal. Small, repeated exposures may gradually depress the cholinesterase activity to very low levels, often resulting in minimal symptoms. References: The Essentials of Forensic Medicine & Toxicology, KS Narayan Reddy, 35th edition, Page No. 396.

Pralidoxime(2-PAM), a nucleophilic oxime, most effective when treatment is started early and if used within 48 hours and helps in regenerating AChE associated with skeletal muscle neuromuscular junctions(overcome the nicotinic effects of OPCs). Dose: 1-2 g IV(20-40 mg/kg) over 5-20 min dissolved in 0.9% normal saline solution, may be repeated at 1-2 hours if muscle weakness is not relieved and again after 8-10 hours. Alternatively, continuous infusion(200-400 mg/h) of 2-PAM is more effective because of shorter duration of action of a single dose. Reference: Review of Forensic medicine and Toxicology, Gautam Biswas, 5 th edition, Page No. 655.

Atropinization: Atropine blocks the muscarinic manifestations and has no effect on nicotinic receptors(on muscle weakness or paralysis) and does not affect the rate of regeneration of inhibited AChE. Dose: 2-4 mg IV(0.05-0.2 mg/kg in children) repeated after every 5-15 minutes till atropinization, the dose should be adjusted to maintain this effect for at least 24 hours(maintenance dose: 0.02-0.05 mg/kg). Option A: OP compounds are anti-cholinesterase agents(ChE inhibitors) Option B: The muscarinic manifestations may lead to bradycardia or tachycardia; but predominantly bradycardia. Option D: Nicotinic manifestations on striated muscle leads to initial stimulus results in contraction. Later there is paralysis due to persistent depolarisation. Reference: Review of Forensic medicine and Toxicology, Gautam Biswas, 5 th edition, Page No. 655.

Explanation: Atropinization: Atropine blocks the muscarinic manifestations and has no effect on nicotinic receptors (on muscle weakness or paralysis) and does not affect the rate of regeneration of inhibited AChE. Dose: 2-4 mg IV (0.05-0.2 mg/kg in children) repeated after every 5-15 minutes till atropinization, the dose should be adjusted to maintain this effect for at least 24 hours (maintenance dose: 0.02-0.05 mg/kg). Anti-cholinesterase agents (Option A): Organophosphorus compounds (OPC) are irreversible acetylcholinesterase (IACh) inhibitors, causing ACh buildup. Bradycardia (Option B): Seen due to excess acetylcholine acting on muscarinic receptors. Paralysis (Option D): A late nicotinic effect due to persistent depolarization at neuromuscular junctions.