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# Pralidoxime

An oxime that reactivates acetylcholinesterase blocked by organophosphate pesticides. It is always given with atropine, never instead of it.

Updated 2026-11-01

- Class: [Specific antidotes](https://durgical.com/en/pharmacology/classes/specific-antidotes/)
- Enzyme: Acetylcholinesterase inhibited by an organophosphate
- ATC code: V03AB04

Also called: 2-PAM, pralidoxime chloride

✂**Acetylcholinesterase inhibited by an organophosphate**Pralidoxime

ⓘ The figure shows human acetylcholinesterase phosphorylated by paraoxon with pralidoxime (2-PAM) in its gorge.

**Target in 3D:** Acetylcholinesterase inhibited by an organophosphate. PDB structure 5HFA (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/5HFA) · Drag to rotate · pinch to zoom

## Mechanism of action

Organophosphates phosphorylate the serine of acetylcholinesterase, so acetylcholine accumulates and overstimulates muscarinic and nicotinic receptors and the brain. Pralidoxime pulls the phosphate group off the enzyme and frees it, mainly at the neuromuscular junction, restoring muscle strength and breathing. It works only before the phosphorylated enzyme «ages» into a permanent bond, so it is given early. It acts mostly outside the brain; atropine is still needed to block muscarinic effects.

- Organophosphate phosphorylates acetylcholinesterase
- Acetylcholine builds up: cholinergic crisis
- Pralidoxime removes the phosphate before ageing
- The enzyme works again: muscles and breathing recover

## Pharmacokinetics

**Distribution**
Distributes in extracellular water; not bound to plasma proteins; little enters the brain

**Elimination**
Rapidly excreted in urine by tubular secretion, partly unchanged; it accumulates in kidney failure

**Half-life**
Short, a few hours at most, so repeated doses or a continuous infusion are used

## Indications

- Severe organophosphate pesticide poisoning (with atropine), pesticides caused about a third of the suicidal poisonings reported in Colombia in 2015
- Nerve agent poisoning

## Adverse effects

### Common

- Blurred vision and double vision
- Dizziness, headache and drowsiness
- Nausea
- Raised blood pressure and tachycardia
- Pain at the intramuscular injection site

### Serious (rare, important)

- Rapid intravenous injection can cause laryngospasm, muscle rigidity and cardiorespiratory arrest
- Muscle weakness that is hard to tell apart from the poisoning itself

## Contraindications

- No absolute contraindications in severe poisoning; known hypersensitivity is relative
- Carbamate poisoning: oximes are generally avoided because they may worsen some carbamates
- Poisoning by phosphorus, inorganic phosphates or organophosphates without anticholinesterase activity: no effect

## Key interactions

**Atropine**
Given together; signs of atropinisation (flushing, mydriasis, tachycardia, dry mouth) may appear earlier

**Carbamate insecticides (e.g. carbaryl)**
Oximes may increase their toxicity

## What is monitored

- Muscle strength, respiratory effort and oxygen saturation
- Heart rate and blood pressure
- Kidney function
- Red-cell and plasma cholinesterase levels (treatment is not delayed for them)

## Administration and safety

- Given intravenously as a slow infusion, or intramuscularly when no vein is available
- Never as a rapid intravenous push
- Started as early as possible, before the enzyme ages
- Preferably in an intensive care unit, by experienced staff

## Nursing care

- Decontaminate first: remove clothes and wash the skin, with protective equipment for staff
- Assess secretions, breathing and pupils repeatedly while atropine is titrated
- Watch for fasciculations and weakness of neck and breathing muscles
- Monitor urine output and kidney function
- Ask about intent; pesticide self-poisoning needs mental-health follow-up

## Pregnancy and breastfeeding

Data in pregnancy are limited; the Colombian guide lists it as category C and advises against breastfeeding during treatment.

## Memory aid

Atropine dries, pralidoxime frees: atropine treats the «wet» muscarinic signs, the oxime frees the enzyme for the muscles, and only before it ages.

## Test yourself

Think of the answer, then tap the question to see it.

## Why is pralidoxime given early in organophosphate poisoning?

The phosphorylated enzyme «ages» into a permanent bond; after that it can no longer be reactivated.

## Why is atropine still needed with pralidoxime?

Pralidoxime acts mainly at nicotinic sites outside the brain; atropine blocks the muscarinic effects such as bronchorrhoea and bradycardia.

## In which pesticide poisoning are oximes generally avoided?

Carbamates: they inhibit the enzyme reversibly and oximes may worsen some of them.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Guía para el Manejo de Emergencias Toxicológicas](https://minsalud.gov.co/sites/rid/Lists/BibliotecaDigital/RIDE/DE/GT/guias-manejo-emergencias-toxicologicas-outpout.pdf) (Ministerio de Salud y Protección Social; Organización Panamericana de la Salud, 2017); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=V03AB04) (WHO Collaborating Centre for Drug Statistics Methodology, 2026); [RCSB PDB - 5HFA: Crystal structure of human acetylcholinesterase in complex with paraoxon and 2-PAM](https://www.rcsb.org/structure/5HFA) (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.

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