How to give pralidoxime injection in OP poisoning?
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pralidoxime injection dose administration OP organophosphate poisoning protocol
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I now have comprehensive information from the textbooks and clinical sources. Here is a complete answer:
Pralidoxime (2-PAM) in Organophosphate (OP) Poisoning
Mechanism
Pralidoxime is an oxime that displaces the organophosphate molecule from the active site of acetylcholinesterase (AChE), reactivating the enzyme. It acts at both nicotinic and muscarinic receptors (and CNS), and is the only drug that reverses muscle paralysis in OP poisoning. It is always used alongside atropine (which covers muscarinic effects only).
Critical timing: Pralidoxime must be given as early as possible, before "aging" - the irreversible phosphorylation of AChE. However, it is still recommended up to 24-48 hours after exposure, and in severe poisoning some evidence supports multiple doses over several days.
Dosing - Adults
WHO-recommended regimen (Tintinalli's EM):
- Loading dose: 30 mg/kg IV bolus (up to 1-2 g), mixed in normal saline, infused over 5-10 minutes (or over 15-30 min if pulmonary edema is present)
- Maintenance: Continuous infusion of 8 mg/kg/hour for 24-48 hours
Alternative (Medscape/Protopam label):
- 1-2 g IV (10-20 mg/mL solution) over 15-30 minutes
- Repeat after 1 hour if muscle weakness persists
- Then every 8-12 hours as needed
If IV access is not possible:
- IM or SC route can be used: 30 mg/kg IM/SC
If rapid IV infusion is required (e.g., pulmonary edema):
- 50 mg/mL solution over 5 minutes (slower preferred to avoid adverse effects)
Dosing - Pediatric (up to 16 years)
- Loading dose: 20-50 mg/kg IV (max 2000 mg/dose) as a 10-20 mg/mL solution over 15-30 minutes
- Maintenance: Continuous infusion of 10-20 mg/kg/hour
- OR: Repeat dose after 1 hour if needed, then every 10-12 hours
Nerve Agent Poisoning (IM auto-injector use)
- 600 mg IM x3 doses (each 15 minutes apart) for mild symptoms; rapid succession for severe
- Max initial total dose: 1800 mg
- May repeat the 3-dose series 1 hour after the last injection if symptoms persist
Duration
- Continue pralidoxime for 24-48 hours while monitoring AChE levels
- End point: absence of signs and symptoms on withholding the drug
- Fat-soluble organophosphates (e.g., some nerve agents) may require weeks of therapy while awaiting new enzyme synthesis
Key Points and Cautions
| Point | Detail |
|---|---|
| Give ASAP | Before AChE "aging" renders reactivation impossible |
| Always combine with atropine | Atropine covers muscarinic signs; 2-PAM covers nicotinic + muscarinic + CNS |
| Do NOT give too fast | Rapid IV bolus can cause tachycardia, laryngospasm, muscle rigidity, hypertension |
| Carbamates | Generally avoid pralidoxime in carbaryl (carbamate) poisoning - it may potentiate toxicity. However, use it in mixed or unknown exposures |
| Asymptomatic patients | Not recommended |
| Renal impairment | Reduce dose (drug is renally excreted) |
| Myasthenia gravis | Use with great caution - may precipitate myasthenic crisis |
Preparation
Pralidoxime chloride 1 g powder for injection is reconstituted in 20-100 mL of normal saline to give a 10-20 mg/mL concentration for IV infusion. For emergency IM use, it can be given as a more concentrated solution (50 mg/mL).
Sources: Tintinalli's Emergency Medicine: A Comprehensive Study Guide (Table 201-3); Medscape Pralidoxime Dosing; FDA Protopam Label
If weight is 70 kg how much should be given and how?
Based on the dosing regimens already established, here is the calculated dose for a 70 kg adult:
Pralidoxime for a 70 kg Patient
Loading Dose
WHO regimen: 30 mg/kg × 70 kg = 2100 mg → round down to 2 g (2000 mg)
(2 g is the standard maximum loading dose)
Preparation:
- Take 2 vials of pralidoxime chloride (1 g each)
- Dissolve each in 20 mL normal saline (NS) → 40 mL total → concentration = 50 mg/mL
- Dilute further into 100 mL NS → final concentration = ~20 mg/mL
- Infuse IV over 15-30 minutes (never as a rapid IV push)
Maintenance Infusion
8 mg/kg/hour × 70 kg = 560 mg/hour ≈ 500-600 mg/hour
Preparation:
- Add 6 g pralidoxime (6 vials) to 500 mL NS
- Concentration = 12 mg/mL
- Run at 42-50 mL/hour to deliver ~500-600 mg/hour
- Continue for 24-48 hours
Step-by-Step Administration
| Step | Action |
|---|---|
| 1 | Ensure IV access is established (large bore) |
| 2 | Give atropine first (or simultaneously) - atropine takes priority for muscarinic symptoms |
| 3 | Reconstitute 2 g pralidoxime in 100 mL NS |
| 4 | Infuse loading dose over 15-30 min via infusion pump or drip |
| 5 | Monitor for adverse effects during infusion (tachycardia, hypertension, laryngospasm) |
| 6 | Start maintenance infusion immediately after loading dose |
| 7 | Reassess muscle strength 10-40 min after loading dose |
| 8 | Continue for 24-48 h; stop when symptoms resolve on withholding |
If No IV Access (Emergency)
- Give 2 g IM (as 50 mg/mL solution = 40 mL, split across multiple sites) or use auto-injector if available
- Establish IV access as soon as possible and switch to infusion
Red Flags During Infusion - Slow Down or Stop If:
- Sudden hypertension
- Tachycardia worsening (not due to OP)
- Laryngospasm or muscle rigidity
- These resolve when infusion rate is reduced
Bottom line for a 70 kg patient: Load with 2 g IV over 15-30 min, then run 500-600 mg/hour as a continuous infusion for 24-48 hours, always alongside adequate atropinization.
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