Paediatrics: Poisoning: antidotes and substrates

Poisoning: antidotes and substrates

Antidotes and substrates are useful in only a minority of poisonings. Poison centres will provide exact advice.

Antidotes and substrates

Paracetamol (acetaminophen)

·  Children taking >150mg/kg need assessment

·  Take blood 4hr after ingestion and use nomogram. Give N-acetylcysteine if criteria are met. Check liver function tests (LFTs) and International normalized ratio (INR)

·  N-acetylcysteine: PO or NG loading 140mg/kg, then 70mg/kg/ dose qds for 17 doses. IV used if GI bleeding. Repeat blood level at 24hr

Anticholinergics, antihistamines (diphenhydramine), plants (deadly nightshade, jimson weed, henbane), anti-Parkinsonian drugs, dilating eye drops, skeletal muscle relaxants

·  Benzodiazepines: used for agitation and seizures (avoid phenytoin)

·  Physostigmine: useful for anticholinergic syndrome. It reverses central effects of agitation and seizures. Not for tricyclic antidepressant overdose, asthmatics, GI obstruction, genitourinary (GU) obstruction. Give slow IV 20micrograms/kg/dose (up to 500micrograms) over 5min. Repeat every 5min, but maximum cumulative dose should be below 2mg. Have atropine available for cholinergic symptoms (0.5mg for every mg of physostigmine). Response is rapid

Benzodiazepines: chlodiazepoxide, clonazepam, diazepam, temazepam

·  If ABCs are stable there is little need to do more than observe

·  Flumazenil. Reverses lethargy and coma. Not for tricyclic antidepressant or chloral hydrate overdose, or child with seizure disorder on benzodiazepines. Give 10micrograms/kg over 1min (maximum 500micrograms/dose, or 1mg overall). Response is rapid, but resedation may occur. May induce seizures

β-adrenergic antagonists: atenolol, esmolol, labetalol, propranolol

·  Glucagon is useful for reversing bradycardia and hypotension. Give 0.05–0.1mg/kg bolus, followed by 0.1mg/kg/h infusion

·  Atropine, isoprenaline, and amiodarone can be used if bradycardia or hypotension persist after glucagon

Cardiac pacing may be needed. If cardiac arrest occurs, massive doses of adrenaline (epinephrine) may be required

Calcium channel blockers: diltiazem, nifedipine, nimodipine, verapamil

·  Use glucagon, amrinone, isoprenaline, atropine, and dopamine for hypotension unresponsive to fluids and calcium

·Give calcium chloride (20mg/kg of 10% solution) or calcium gluconate (100mg/kg of 10% solution) for hypotension and bradyarrhythmias

·Consider cardiac pacing

Carbon monoxide (CO) fire; exhaust from fuel engines, furnaces, or burners; paint remover with methylene chloride

·Ensure ABCs and give 100% oxygen

·Check COHb level

·Consider hyperbaric oxygen if COHb >40%, or if symptoms persist after 4h despite 100% oxygen

·Also consider cyanide toxicity if smoke inhalation

Cyanide

·There are special kits for rescue that will be in Pharmacy

·Sodium nitrate 3%: dose depends on Hb level, but do not give if CO poisoning as well

·Sodium thiosulphate 25%: dose depends on Hb level

Digoxin

·Measure serum drug level. Toxicity occurs with level >2ng/mL

·Check electrolytes, magnesium, thyroxine, and calcium

·Correct hypokalaemia (IV 0.5–1mmol/kg/dose as infusion 0.5mmol/kg/h over 2hr)

·If hyperkalaemic (>5mmol/L) give insulin, dextrose, sodium bicarbonate, and Kayexalate^®. Do not give calcium chloride or calcium gluconate because these potentiate ventricular arrhythmias

·Digoxin-specific antibody (FAB fragments). Give for ventricular dysrhythmias, or supraventricular bradyarrhythmias (if resistant to IV atropine 10–20micrograms/kg), hyperkalaemia, hypotension, heart block, and ingestion >4mg. Phenytoin may be used to improve AV conduction. Avoid quinidine, procainamide, isoprenaline, or disopyramide if AV block present

Ethylene glycol, methanol

·Fomepizole (loading 15mg/kg, then 10mg/kg bd for 4 doses, then 15mg/kg bd until levels 20mg/dL): antidote for methanol and ethylene glycol. Indications: level 20mg/dL, or high anion gap metabolic acidosis

·If not available, use ethanol (loading dose 0.6g/kg; load over 1hr followed by infusion 100mg/kg/hr)

·Other agent: pyridoxine 2mg/kg and thiamine 500micrograms/kg. In the case of methanol, also give folate (50–100mg over 6hr)

Iron

·Measure serum concentration 2–6hr after ingestion. A level >350micrograms/dL is frequently associated with systemic toxicity. If ingestion <20mg/kg no treatment needed

·Desferrioxamine: IV infusion 5–15mg/kg/hr in all cases of serious poisoning (i.e. based on symptoms, AXR, serum level >500micrograms/dL). Continue until symptoms have resolved

Isoniazid

For stopping seizure use pyridoxine (vitamin B₆) 3–5g

Lead

·  Immediate intervention for blood level  70micrograms/dL

·  Oral chelation with dimercaptosuccinic acid (DMSA): first 5 days 30mg/ kg/day divided every 8hr; next 14 days 20mg/kg/day divided every 12hr

·  Parenteral chelation with British antilewisite (BAL): initial dose 75mg/ m² deep IM; then 4hr later start CaNa₂EDTA (1500mg/m²/day via continuous IV infusion for 48hr). If there is risk of cerebral oedema, then give IM. BAL is continued simultaneously at 75mg/m²/dose IM 4-hourly for 48hr

·  BAL is suspended in peanut oil, and may cause haemolysis in patients with G6PD deficiency

Methaemoglobinaemia: sulphonamides, quinines, phenacetin, nitrates, aniline dyes, naphthalene

·  Measure level and if >30% start treatment

·  Methylene blue 1%: 1–2mg/kg (0.1–0.2mL/kg) IV over 5min. May repeat dose (maximum total 7mg/kg) if symptoms present after 1hr

·  Beware of methylene blue in G6PD deficiency

·  Consider hyperbaric oxygen or exchange transfusion if no response

Narcotics: codeine, dextromethorphan, propoxyphene, pentazocine, butorphanol, methadone

·  Naloxone useful for reversing coma caused by opiates. Give IV, IM, or via ETT 2mg (10micrograms/kg, if < 12yrs) inc to 100micrograms/ kg. Response is rapid and repeat doses or infusion can be used.

Organophosphates: pesticides

·  Atropine: initial dose 20micrograms/kg (max 2mg) IV; then additional doses if bronchorrhoea

·  Pralidoxime: 25–50mg/kg/dose (up to 1g) IV; consider 10–15mg/kg/hr infusion for severe cases

Phenothiazine

·  For extrapyramidal syndrome, diphenhydramine: 1mg/kg/dose slow IV over 5min.

·  Also if life-threatening, IV benzatropine 20–50micrograms/kg/dose (1–2 doses per day in children >3yrs)