Organophosphorus (OP) Poisoning Pathway

Peradeniya Scale, Atropinisation & Oxime Protocol
Clinical Note: This pathway integrates the Peradeniya OP Poisoning (POP) Scale with the rapid doubling Atropine titration protocol and renal-adjusted Pralidoxime (PAM) administration.

1. Patient Characteristics & Renal Function

2. Toxidrome & Vitals

3. Peradeniya OP Poisoning (POP) Scale

Fields marked with ● are auto-populated from vitals above.

⚒ Clinical Context & Pearls

Organophosphorus (OP) pesticide poisoning is a major public health concern in rural Indian centres. Rapid identification of the toxidrome (DUMBELS) and aggressive early management dictate survival.

⚠ DO NOT BE TIMID WITH ATROPINE IN OP POISONING

The sheer volume of Atropine required to treat severe organophosphorus poisoning often shocks junior physicians. Daily requirements can routinely exceed 1,000 mg to 3,600 mg/day, and literature documents massive cumulative doses exceeding 11 grams over a week. The limit of Atropine is not a predetermined "maximum daily allowance," but rather the physiological endpoint. As long as the patient's chest remains "wet" with crackles, they remain under-atropinised.

Follow the D-O-U-B-L-E Rule for Atropinisation:

  • D — Do not be timid! There is no predetermined maximum dose limit.
  • O — Observe the chest. Resolution of bronchorrhoea is your primary target.
  • U — Up the dose (double it). If the chest is still wet after 5 minutes, give twice the previous dose.
  • B — Bradycardia. A heart rate under 80 bpm means you need to give more.
  • L — Limitless ceiling. Titrate strictly to the physiological effect, not to ampoule counts.
  • E — Every 5 minutes. Reassess and administer the next bolus rapidly.

The Pitfall of Serum Pseudocholinesterase

While measuring serum pseudocholinesterase (butyrylcholinesterase) is frequently ordered to confirm organophosphorus exposure, relying on it to guide acute management is a critical error.

  • Early False Reassurance: If blood is drawn very early post-ingestion (within the first few hours), the level is often completely normal because systemic enzyme inhibition is not yet complete. Never withhold antidotes if the clinical toxidrome is present.
  • Zero Resuscitation Value: Serum levels do not reliably correlate with clinical severity, the degree of true acetylcholinesterase inhibition at the neuromuscular junction, or the risk of respiratory failure.
  • Serial Monitoring is Obsolete: Serial laboratory monitoring is not recommended. Atropine and Pralidoxime titration must be dictated entirely by physiological endpoints (clear chest, heart rate > 80 bpm), never by attempting to correct a laboratory value.

1. The Target of Atropinisation

Atropine reverses muscarinic effects (bronchorrhoea, bradycardia, miosis) but has no effect on nicotinic receptors (muscle weakness, fasciculations). The primary therapeutic endpoint is a clear chest.

  • Clear Chest: Resolution of bronchorrhoea and crackles.
  • Heart Rate: > 80 bpm.
  • Blood Pressure: Systolic > 80 mmHg.
  • Pupils: No longer pinpoint (pupil size is a secondary, less reliable marker).

2. The Doubling Dose Protocol

Under-dosing Atropine is a common cause of mortality. Guidelines favour a rapid doubling approach:

  • Administer initial bolus (e.g., 2-3 mg).
  • Review at 5 minutes. If no improvement, double the dose (4 mg, then 8 mg, then 16 mg).
  • Once atropinised, establish a maintenance infusion at 10% to 20% of the total loading dose per hour.
Important Consideration: Intermediate Syndrome
Occurs 24 to 96 hours post-ingestion. Characterised by weakness of proximal limb muscles, neck flexors, and respiratory muscles. Atropine is ineffective for intermediate syndrome. Patients require mechanical ventilation until neuromuscular transmission recovers.
Abbreviations: OP (Organophosphorus) · POP (Peradeniya OP Poisoning) · PAM (Pralidoxime) · HDU (High Dependency Unit) · ICU (Intensive Care Unit) · CrCl (Creatinine Clearance) · IV (Intravenous) · HR (Heart Rate) · BP (Blood Pressure) · bpm (Beats Per Minute)
Algorithm References & Evidence Base
  1. Eddleston M, et al. Early management after self-poisoning with an organophosphorus or carbamate pesticide. Lancet. 2008;371(9612):597-607.
  2. Senanayake N, Karalliedde L. Scale to assess severity in organophosphorus intoxication: POP scale. Hum Exp Toxicol. 1993;12(4):297-299.
  3. Roberts D, Aaron C. Management of acute organophosphorus pesticide poisoning. BMJ. 2007;334(7594):629-634.
  4. Indian Society of Toxicology. Guidelines for the management of pesticide poisoning in India. J Emerg Trauma Shock. 2011;4(1):112-118.
How to Cite This Tool

AMA Style:
Umakanth S. Organophosphorus (OP) Poisoning Pathway. MEDiscuss. Published 2026. Accessed .

Vancouver Style:
Umakanth S. Organophosphorus (OP) Poisoning Pathway [Internet]. MEDiscuss.org; 2026 [cited ]. Available from:

⚠ Disclaimer: This decision-support system is intended for healthcare professionals. It does not substitute clinical judgment. These algorithms are evidence-based, but medical knowledge evolves continuously. The treating physician retains absolute responsibility for all diagnostic, dosing, and therapeutic decisions. Always verify outputs against current institutional protocols and individual patient contexts.
© 2026 MEDiscuss.org. All rights reserved. This CDSS Module was designed and developed by
Dr. Shashikiran Umakanth using the available evidence base. Provided free of charge for clinical use. Unauthorised reproduction or redistribution is strictly prohibited.
Category Therapeutic Pathways & Algorithms
Specialties Internal Medicine, Toxicology, Critical Care
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