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Emergency And Acute Medicine – Poisoning, Antidotes
Antidote therapy is used in specific toxicologic emergencies and should be administered in conjunction with supportive care and consultation with a poison control center or medical toxicologist when appropriate.
N-acetylcysteine (NAC) is indicated for acetaminophen overdose. It is most effective when given within the first 8 hours after ingestion. Common adverse effects include unpleasant odor, nausea, and vomiting. Oral dosing consists of 140 mg/kg followed by 70 mg/kg every 4 hours for 17 doses. Intravenous dosing includes 150 mg/kg in 200 mL D5W over 60 minutes, then 50 mg/kg in 500 mL D5W over 4 hours, followed by 100 mg/kg in 1,000 mL D5W over 16 hours. In pediatric patients, IV fluid volumes must be reduced to avoid fluid overload and hyponatremia.
Atropine is used for bradycardia due to drugs and for organophosphate insecticide poisoning. Caution is advised in myasthenia gravis, narrow-angle glaucoma, hypertension, coronary ischemia, and urinary obstruction. Adult dose is 1–2 mg IV. Pediatric dose is 0.02 mg/kg IV (minimum 0.1 mg). Large repeated doses may be required in organophosphate poisoning.
Benztropine (Cogentin) is indicated for acute dystonic reactions. It should be used cautiously in carbamate exposure, myasthenia gravis, narrow-angle glaucoma, hypertension, coronary ischemia, and urinary obstruction. Adult dosing is 1–2 mg IV for acute reactions or orally for prevention. Pediatric dose is 0.02 mg/kg IV or PO.
Benzodiazepines are indicated for agitation, stimulant toxicity, and seizures. Respiratory and CNS depression are potential adverse effects. Midazolam dosing is 1 mg IV or IM every 2–3 minutes as needed in adults, and 0.1 mg/kg IV or IM in children. Diazepam dosing is 2–5 mg IV or IM in adults (repeat in 10–15 minutes) and 0.1 mg/kg IV or IM in pediatrics.
Sodium bicarbonate is used for tricyclic antidepressant poisoning, metabolic acidosis, and urinary alkalinization. Adverse effects include congestive heart failure, excessive alkalosis, and hypokalemia. For serum alkalinization, give 1 mEq/kg IV push. For urine alkalinization, administer 100–150 mEq in 1 L D5W at 2–3 mL/kg/hour IV with a urine pH goal of 7–8.
Black widow spider antivenin (Latrodectus mactans) is indicated for severe hypertension and muscle spasms not relieved by analgesics and muscle relaxants, and may be considered in young children, elderly patients, and pregnant women with threatened abortion. It is equine-derived and may cause immediate hypersensitivity or delayed serum sickness. Dose is 1–2 vials IM or slow IV over 15–30 minutes; dilute one vial in 50 mL saline for IV use.
Botulinum antitoxin (trivalent A, B, E) is indicated in clinical botulism before onset of paralysis. It binds only free toxin and is not used for infant botulism. It is equine-derived with risk of hypersensitivity. Administer 1–2 vials IV every 4 hours for 4–5 doses after reconstitution.
Calcium is indicated for hyperkalemia with cardiac toxicity, hydrofluoric acid burns, calcium channel blocker overdose, and citrate, oxalate, or phosphate poisoning. Avoid in digoxin toxicity and hypercalcemia. Adult dose is 5–10 mL of 10% calcium chloride or 10–20 mL of 10% calcium gluconate IV. Pediatric dose is 0.1–0.2 mL/kg of 10% calcium chloride or 0.2–0.3 mL/kg of 10% calcium gluconate IV.
Calcium EDTA is used for lead and certain heavy metal toxicities. It may cause nephrotoxicity and other adverse effects. Dose is 1 g/m²/day IV over 8–12 hours for 5 days, with repeat cycles guided by blood lead levels.
Cyanide poisoning can be treated with a cyanide antidote kit or hydroxocobalamin. The cyanide kit includes amyl nitrite (inhaled until IV access is established), sodium nitrite (300 mg IV in adults; 0.3 mL/kg of 3% solution in children), and sodium thiosulfate (12.5 g IV in adults; 50 mg/kg in children). Hydroxocobalamin is given as 5 g IV over 15 minutes in adults, repeatable once; suggested pediatric dose is 70 mg/kg IV.
Dantrolene is indicated for malignant hyperthermia, neuroleptic malignant syndrome, serotonin syndrome, and severe muscle rigidity. Dose is 1–2 mg/kg IV bolus, repeated every 10–15 minutes as needed, maximum 10 mg/kg.
Deferoxamine treats iron toxicity. It should not be used for more than 24 hours due to risk of delayed ARDS. Dose is 10–15 mg/kg/hour IV, increased in severe cases.
Digoxin-specific antibody fragments (Digibind) are used in digoxin or digitoxin toxicity. One vial (40 mg) binds 0.6 mg digoxin. Dose estimation is based on serum level and patient weight, with typical dosing of 10–20 vials in acute overdose and 4–6 vials in chronic toxicity.
Dimercaprol (BAL) is indicated for arsenic, gold, mercury, and severe lead toxicity with encephalopathy. Dose is 3 mg/kg IM every 4 hours for 2 days, then every 12 hours for 7 days.
Flumazenil reverses benzodiazepine effects but is contraindicated in tricyclic antidepressant overdose and may precipitate seizures or withdrawal. Adult dose is 0.2 mg IV slow push, repeated every 2–3 minutes up to 1 mg. Pediatric dose is 0.01–0.05 mg/kg IV.
Fomepizole is used for methanol and ethylene glycol toxicity. Dose is 15 mg/kg IV loading, then 10 mg/kg every 12 hours for four doses, then 15 mg/kg every 12 hours thereafter.
Glucagon is used for β-blocker or calcium channel blocker overdose with bradycardia or hypotension. Adult dose is 5–10 mg IV over 1 minute; pediatric dose is 0.15 mg/kg IV.
High-dose insulin with glucose is used in severe calcium channel blocker overdose or hyperkalemia refractory to other therapy. Close glucose monitoring is required.
Naloxone (Narcan) reverses opioid toxicity. Adult dose is 0.4–2 mg IV or IM, repeat up to 10 mg. Pediatric dose is 0.1 mg/kg IV or IM. Acute withdrawal and agitation may occur.
Octreotide treats sulfonylurea-induced hypoglycemia. Adult dose is 50 micrograms subcutaneously every 6 hours. Pediatric dose is 4–5 micrograms/kg/day divided every 6 hours.
Pralidoxime (2-PAM) is used in organophosphate toxicity in conjunction with atropine. Adult dose is 1–2 g IV over 15 minutes, repeat as needed. Pediatric dose is 25–50 mg/kg over 15 minutes.
Protamine reverses heparin anticoagulation. Dose is 1 mg per 100 IU of heparin administered, given slowly IV.
Pyridoxine (vitamin B6) is used for isoniazid-induced seizures. If ingestion amount is unknown, give 5 g IV in adults or 1 g in children.
Vitamin K (phytonadione) reverses warfarin anticoagulation. Dose ranges from 2–10 mg PO or slow IV, repeat as needed based on INR.
Hyperbaric oxygen is indicated for severe carbon monoxide poisoning.
Many antivenins, including those for coral snake and rattlesnake envenomation, are animal-derived and carry risk of hypersensitivity and serum sickness. Premedication and close monitoring are required.
Antidote therapy should always accompany appropriate supportive care, monitoring, and consultation with poison control.
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