Organophosphorus (OP) Poisoning Pathway

The Peradeniya score, atropine titrated to effect, and a renally adjusted oxime · v1.3

  • Enter the age, weight, serum creatinine and the six Peradeniya scale findings.
  • Say which compound is suspected. Pralidoxime is withheld rather than dosed where a carbamate is selected.
  • You get the severity graded on the Peradeniya organophosphorus poisoning scale, the rapid doubling atropine titration, and a pralidoxime dose adjusted for renal function.
  • Titrate atropine to the five bedside endpoints, not to a ceiling dose: a clear chest with no wheeze, a heart rate above 80 bpm, a systolic blood pressure above 80 mmHg with urine flowing, dry axillae, and pupils that are no longer pinpoint.

  • Decontamination, the airway and intermediate syndrome, which appear here only as prompts in the action plan. Their conduct, and the management of intermediate syndrome over the days that follow, belongs to the ICU.
  • Poisoning by anything other than an organophosphorus or carbamate compound. Aluminium phosphide, paraquat and the pyrethroids behave differently and are not graded by this scale.
  • The renal adjustment in a child. Atropine and pralidoxime are both dosed by weight, but the clearance that halves the pralidoxime infusion is Cockcroft-Gault, an adult equation, and the Peradeniya bands were derived in adults.
  • Grading from serum or red cell cholinesterase. The severity here is the clinical Peradeniya score, for the reasons Pearls gives.
  • Ventilator settings, and the psychiatric assessment that has to follow a deliberate ingestion.

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 pesticide poisoning fills beds in every district hospital in rural India, and most of those patients arrive within an hour or two of ingestion. Recognise the cholinergic toxidrome (DUMBELS), atropinise early, and keep going until the chest is clear. Outcome turns on how quickly that first hour is used.

1. Atropine Is Titrated to Effect, Not to a Ceiling

The quantity of atropine a severe organophosphorus poisoning needs is far larger than anything a resident meets elsewhere. Daily requirements of 1,000 mg to 3,600 mg/day are ordinary, and cumulative doses beyond 11 grams over a week are documented. There is no maximum daily allowance to work to. The endpoint is physiological: while the chest is still wet with crackles, the patient is under-atropinised, whatever the running total says.

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

  • D: Dose without a ceiling. No maximum daily dose has been set for this indication.
  • 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 the dose so far has not been enough.
  • L: Look at the patient, not the ampoule count. Titrate to the physiological effect.
  • E: Every 5 minutes. Reassess and administer the next bolus rapidly.

2. The Limitation of Serum Pseudocholinesterase

Serum pseudocholinesterase (butyrylcholinesterase) is often sent to confirm exposure, and for that it is reasonable. Using it to guide acute management is where it misleads.

  • 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.
  • No Value During Resuscitation: Serum levels do not track clinical severity, the true degree of 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.

3. The Endpoints of Atropinisation, and the Doubling Protocol

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. Under-dosing atropine is one of the commonest reasons these patients die, so guidelines favour rapid doubling.

  • 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).
  • The doubling protocol: administer an initial bolus (e.g., 2-3 mg); review at 5 minutes and, if there is 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.

4. The Intermediate Syndrome

Point to note. It appears 24 to 96 hours after ingestion, in a patient who looked to be recovering. Weakness affects the proximal limb muscles, the neck flexors and the respiratory muscles. Atropine does nothing for it. These patients need mechanical ventilation until neuromuscular transmission recovers, so the ventilator is planned for rather than improvised.
Abbreviations: AKI (Acute Kidney Injury) · BMI (Body Mass Index) · BP (Blood Pressure) · bpm (Beats Per Minute) · CrCl (Creatinine Clearance) · DUMBELS (Diarrhoea, Urination, Miosis, Bradycardia, Emesis, Lacrimation, Salivation) · HDU (High Dependency Unit) · HR (Heart Rate) · ICU (Intensive Care Unit) · IV (Intravenous) · OP (Organophosphorus) · PAM (Pralidoxime) · POP (Peradeniya OP Poisoning) · sCr (Serum Creatinine)
References
  1. Eddleston M, Buckley NA, Eyer P, Dawson AH. Management of acute organophosphorus pesticide poisoning. Lancet. 2008;371(9612):597-607. PMID 17706760.
  2. Eddleston M, Dawson A, Karalliedde L, et al. Early management after self-poisoning with an organophosphorus or carbamate pesticide: a treatment protocol for junior doctors. Crit Care. 2004;8(6):R391-R397. PMID 15566582.
  3. Senanayake N, de Silva HJ, Karalliedde L. A scale to assess severity in organophosphorus intoxication: POP scale. Hum Exp Toxicol. 1993;12(4):297-299. PMID 8104007.
  4. Roberts DM, Aaron CK. Management of acute organophosphorus pesticide poisoning. BMJ. 2007;334(7594):629-634. PMID 17379909.
  5. Eddleston M, Eyer P, Worek F, et al. Pralidoxime in acute organophosphorus insecticide poisoning: a randomised controlled trial. PLoS Med. 2009;6(6):e1000104. PMID 19564902.
  6. Buckley NA, Eddleston M, Li Y, Bevan M, Robertson J. Oximes for acute organophosphate pesticide poisoning. Cochrane Database Syst Rev. 2011;(2):CD005085. PMID 21328273. Its conclusion, quoted: "The WHO recommended regimen (30 mg/kg pralidoxime chloride bolus followed by 8 mg/kg/hr infusion) is not supported." That is the regimen this tool prints, and it prints it because it is what Indian units stock and follow.
  7. Senanayake N, Karalliedde L. Neurotoxic effects of organophosphorus insecticides. An intermediate syndrome. N Engl J Med. 1987;316(13):761-763. PMID 3029588.
  8. Peter JV, Sudarsan TI, Moran JL. Clinical features of organophosphate poisoning: a review of different classification systems and approaches. Indian J Crit Care Med. 2014;18(11):735-745. PMID 25425841.
  9. Srinivas Rao Ch, Venkateswarlu V, Surender T, Eddleston M, Buckley NA. Pesticide poisoning in south India: opportunities for prevention and improved medical management. Trop Med Int Health. 2005;10(6):581-588. PMID 15941422.

Two entries were corrected on 28 August 2026. The first reference carried the title of the Critical Care 2004 treatment protocol against the citation of the Lancet 2008 seminar; both papers are real, both are by the same first author, and both are now listed separately with their own citations. A fourth entry, Indian Society of Toxicology. Guidelines for the management of pesticide poisoning in India. J Emerg Trauma Shock. 2011;4(1):112-118, could not be traced in PubMed by citation, by journal and year, or by title, and could not be found on a web search on 28 August 2026. It has been withdrawn, and two traceable Indian sources take its place.

How to Cite This Tool

DOIhttps://doi.org/10.5281/zenodo.22401620

AMA Style:Umakanth S. Organophosphorus (OP) Poisoning Pathway. Version 1.3. MEDiscuss Clinical Decision Support System. Published 2026. Accessed . https://mediscuss.org/cdss/op-poisoning. doi:10.5281/zenodo.22401620

Vancouver Style:Umakanth S. Organophosphorus (OP) Poisoning Pathway [Internet]. Version 1.3. MEDiscuss.org; 2026 [cited ]. Available from: https://mediscuss.org/cdss/op-poisoning. doi:10.5281/zenodo.22401620

Disclaimer and scope
Disclaimer: This decision-support system is written for healthcare professionals. It does not substitute clinical judgment, and the treating physician retains absolute responsibility for every diagnostic, dosing and therapeutic decision. The algorithms are built on the evidence as it stands, and the evidence moves. Verify the output against your current institutional protocol, and against the patient in front of you.
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Category Acute ResuscitationPathway
Specialties Internal Medicine, Toxicology, Critical Care

Written and maintained by

Dr Shashikiran Umakanth

Last revised 24 August 2026

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