ANTIHISTAMINESToxic dose Promethazine: >100mg (any ingestion <2yrs, otherwise >2mg/kg)

Loratadine: >40mgToxic Mechanism

Kinda like antipsychotics – they block everythingSedating (1st generation): Competitive inhibition of H1 and M1 Antagonist of α-adrenergic and 5-HT receptors Cardiac Na + K blockade Ca channel blocking, LA effect Cross CNSNon-sedating (2nd generation): Selective competitive reversible inhibitors of peripheral H1 receptor Cardiac K channel blockade Don’t cross CNS

Pharmcology Good PO; sedating more lipid solubleHalf Life Variable; 6-18hrs in sedatingPeak Level 1-3hrs in non-sedating; 2-3hrs in sedatingSymptoms Sedating: CNS and CV SE (may be paradoxical CNS excitation in children)

anticholinergic symptoms – hyperthermia, rhabdo Na blockade possible decr BP / conduction abnormalities, arrhythmias, incr QRS, long QTc Decr seizure threshold (but seizures rare), dystoniaNon-sedating: usually benign; Onset 4-6hrs, offset 12-24hrs; mild sedation, N, ataxia; mild anticholinergic effects; long QTc

Investigations ECG Q4hrlyTreatment Resus: may require inotropic support (if HR <100, isoprenaline 1-10mcg/min or overdrive pace to 100-120)

Low BP responds to IVF, α1 agonist (eg. NAD) If wide QRS / VF/VT: NaHCO3 IV bolus If QT prolongation and TdP: MgSO4 10mmol (0.5mmol/kg) IV over 15minsSupportive: may need physostigmine for anticholinergic SE’s

Decontamination Charcoal OKElimination NoAntidote NoDisposition If asymptomatic and normal ECG at 6hrs (8hrs for 3rd gen ie. Loratadine) home

If symptomatic, cardiac monitor for 12hrsAdmit ICU if: seizures, psychosis, arrhythmias