General Approach and Management of Poisoned Patients Module 6 – Antidotes and Specific Treatments

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Module 6 – Antidotes and Specific Treatments

Learning Objectives

Understand the mechanisms of action, dosing, and monitoring of key antidotes
Apply evidence-based guidelines for antidote use in common toxin exposures
Consider special dosing or contraindications for antidotes in pregnancy and other populations

Key Antidotes

N-Acetylcysteine (NAC): acetaminophen poisoning

– Dose is 150 mg/kg IV x 1, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours

– Oral dose is 140 mg/kg x 1, then 70 mg/kg every 4 hours

– Works by providing glutathione precursor and antioxidant effects

Flumazenil: reverses benzodiazepines

– 0.2 mg IV over 30 seconds with repeat doses q 1 minute as needed

– Maximum 1 mg in benzodiazepine-naive patients or 3 mg if chronic benzodiazepine use

Physostigmine: antidote for anticholinergic syndrome

– Dose 0.5-2 mg IV in adults, 0.02 mg/kg in children

– Contraindicated in tricyclic antidepressant poisoning (risk of seizures)

Antivenom: indicated for black widow spider, scorpion, coral snake, pit viper envenomation

– Dosing depends on type of antivenom – consult poison control

– Use caution in pregnancy due to risk of allergic reaction

Naloxone: reverses opioid overdose

– Initial dose 0.4-2 mg IV – start low to avoid precipitating withdrawal

– May require redosing every 2-3 hours for long-acting opioids

Digoxin immune fab: binds free digoxin to reverse cardiotoxic effects

– Dose is 10-20 vials IV based on level and severity of toxicity

Cyanide antidote kit: combines sodium nitrite, sodium thiosulfate, +/- hydroxocobalamin

– Follow standard dosing for cyanide toxicity

– Obtain IV access above site of cyanide exposure if possible

Antidotes for Toxin-Induced Seizures

– Benzodiazepines (lorazepam, diazepam, midazolam) are first-line for toxin-related seizures

– Phenobarbital or propofol are second-line for refractory status epilepticus

– Avoid phenytoin in cardioactive steroid toxicity (digoxin, oleander) due to potential interaction

– For isoniazid overdose, give IV pyridoxine 5 grams

– For ethylene glycol poisoning, administer fomepizole or ethanol plus thiamine and pyridoxine

Antidotes for Cardiotoxicity

– For calcium channel blocker overdose, give calcium chloride, glucagon, high-dose insulin

– For beta-blocker poisoning, glucagon and high-dose insulin are preferred

– In digoxin toxicity, digoxin immune fab is definitive therapy

– For cyclic antidepressant OD, give 1-2 mEq/kg sodium bicarbonate IV bolus

Antidotes for Methemoglobinemia

– For methemoglobin levels <20%, give 1-2 mg/kg methylene blue IV

– With levels 20-50%, give methylene blue 1-2 mg/kg IV over 5 minutes

– For levels >50%, consider exchange transfusion along with IV methylene blue

Antidotes in Pregnancy

– Naloxone is Category B – carefully titrate to avoid precipitating withdrawal

– Digoxin fab, calcium, and insulin are Category B and appear safe in pregnancy

– Avoid sodium bicarbonate in pregnancy given risk of hypokalemia and uterine tetany

– Thiamine, naloxone, and dextrose are safe and recommended in pregnant patients

In summary, antidotes can be lifesaving when properly matched to the toxicity syndrome. Use appropriate dosing and monitor for adverse effects. Consult poison control experts for guidance.

General Approach and Management of Poisoned Patients

Quizzes

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