Poisoning antidotes and toxicology pharmacology — branching viva

My first moves are ABCDE resuscitation before any antidote. I would secure and protect his airway, support his breathing with bag-valve-mask ventilation because his respiratory rate of eight is inadequate, establish intravenous access, and give a fluid bolus if he is shocked. I would check a bedside glucose immediately because hypoglycaemia mimics poisoning and is instantly reversible. His pin-point pupils and slow breathing are an opioid toxidrome, so I would give naloxone 10 microgram per kilogram intravenously — about 160 microgram — repeated every two to three minutes, titrated to his respiratory rate. I would also take a focused history of what and how much was taken and when, and call the regional poison information centre. [3] [4]

Because the ingestion is staggered and timed-unknown, I would start N-acetylcysteine regardless of a level — the Rumack-Matthew nomogram cannot be applied when timing is uncertain, so the default is to treat. The mechanism is that paracetamol overdose saturates conjugation, shunts metabolism through CYP2E1 to the toxic NAPQI, depletes glutathione, and NAPQI binds hepatocytes; N-acetylcysteine replenishes glutathione. The intravenous regimen for a 16-kilogram child is 150 mg per kilogram over one hour (about 2.4 g), then 50 mg per kilogram over four hours (about 0.8 g), then 100 mg per kilogram over sixteen hours (about 1.6 g) — a 21-hour course. If a reliable level at four hours or later plots on or above the treatment line, that also triggers the course. [1] [2]

No. This is an anaphylactoid reaction that is rate-related, not a true IgE allergy, and it is the commonest adverse effect of N-acetylcysteine. I would pause or slow the infusion, treat the symptoms with an antihistamine, and resume the N-acetylcysteine at a slower rate, because it is rarely a reason to abandon a life-saving course. In a small child I would also watch the diluent volume to avoid fluid overload. [1]

The antidote is deferoxamine, a chelator that binds free ferric iron to form the water-soluble ferrioxamine excreted in the urine. Because he has vomiting, a metabolic acidosis, and an iron exposure, that is significant toxicity, so I would start deferoxamine 15 mg per kilogram per hour intravenously now, titrated to avoid hypotension, and continue it until he is stable, the acidosis resolves, and the urine clears from its vin-rose tint. I would not be reassured by any quiescent phase — iron poisoning has a deceptive interval before shock. A serum iron at three to five hours confirms the burden, but toxicity itself is the trigger to chelate. [8]

For lead, the chelator depends on severity. Oral succimer is used for moderate poisoning, intravenous calcium-disodium EDTA for severe poisoning, and intramuscular dimercaprol is added for lead encephalopathy. The crucial caveat is the TLC trial, which showed that succimer lowered blood lead levels but did not improve neuropsychological outcome at low-to-moderate exposure — so chelation is reserved for higher levels or symptomatic disease, and environmental abatement is emphasised alongside it. The mechanism differs from iron because the chelator and the metal are different. [10]

No, I would not give flumazenil. If this child has taken benzodiazepines and is benzodiazepine-dependent, flumazenil — a competitive benzodiazepine-receptor antagonist — can precipitate refractory seizures, which is why it is not a routine reversal agent. Flumazenil is reserved for the rare, carefully selected reversal of a known pure benzodiazepine overdose in a non-dependent child, and even then with caution. The lesson is that an antidote is not generic — the wrong antidote can be more dangerous than the toxin. [3]

He has renarcotised because naloxone has a short half-life of about 30 to 80 minutes — shorter than most opioids — so it wears off while the opioid persists. I would repeat the naloxone dose titrated to his respiratory rate, and if he re-sedates again or the opioid is long-acting, I would start a naloxone infusion at two-thirds of the effective bolus dose per hour, and observe him in a monitored bed. The principle is titration to respiratory rate, never to full consciousness, to avoid precipitating acute withdrawal. [4]

Three things. First, resuscitation precedes every antidote, and a bedside glucose is never omitted. Second, an antidote is matched to its mechanism and dosed by weight — naloxone for the opioid receptor, N-acetylcysteine for the glutathione substrate, deferoxamine for the iron atom — and the wrong antidote, like flumazenil here, can be more dangerous than the toxin. Third, timing and titration govern safety: default to N-acetylcysteine when paracetamol timing is uncertain, titrate naloxone to respiratory rate and watch for renarcotisation, and start deferoxamine before the iron distributes. With these habits — resuscitate, match the mechanism, dose by weight, and anticipate the mismatch — the poisoned child gets the right reversal at the right moment. [1] [3]