FM13.17 | Therapeutic Drug Overdose: Antipyretics, Anti-infectives & Neuropsychotropics — Summary & Reflection

KEY TAKEAWAYS

Therapeutic drug overdose (FM13.17) spans three major toxidrome groups:

Antipyretics:
- Paracetamol: NAPQI hepatotoxicity (Phase 1 = silent; Phase 3 = fulminant hepatic failure). Antidote: NAC within 8 h (still useful to 24 h); Rumack-Matthew nomogram guides treatment.
- Salicylates: biphasic acid-base; urinary alkalinisation + HD.

Sedative-hypnotics and anticonvulsants:
- Barbiturates: direct Cl⁻ channel opening → fatal respiratory depression; no antidote; ventilatory support.
- Benzodiazepines: GABA-A modulation (ceiling effect); antidote = flumazenil; rarely fatal alone.
- Phenytoin: cerebellar signs + cardiac conduction defects at toxic levels.
- Lithium: narrow TI; tremor → seizures → irreversible cerebellar damage; HD for toxicity.

Neuropsychotropics:
- TCAs: Na⁺ block (QRS widening) + anticholinergic toxidrome; antidote = IV NaHCO₃; lipid emulsion rescue.
- Antipsychotics/haloperidol: QTc prolongation; NMS; magnesium for torsades; dantrolene/bromocriptine for NMS.
- INH overdose: refractory seizures; antidote = IV pyridoxine.

Forensic principle: asymptomatic presentation does NOT exclude significant toxicity (paracetamol, TCA — both can kill while appearing well in early hours).

REFLECT

The 22-year-old woman from the hook scenario is assessed 10 hours after ingestion. Her serum paracetamol plots above the treatment line. She tells you she 'didn't really want to die — just wanted to show how upset she was'. Is this information medically relevant to your decision to start NAC? Is it legally relevant to how the case is documented? How does the Mental Healthcare Act 2017's decriminalisation of attempted suicide change the way you should approach the interaction with this patient and the police officer who brought her in?