Clinical features should manifest within 2 – 4 hours and may last 48 hours (coma usually lasts 24 – 48 hours).
Delayed extrapyramidal effects can occur in children days later.
Children: the toxic dose is unclear but symptoms are likely to develop when >0.5 mg/kg have been ingested.
Can be managed with benzodiazepines (varying doses in the textbooks, easy method is 0.1mg/kg IV for lorazepam (max 4mg) / midazolam (max 10mg) / diazepam (max 10mg).
Check the patient is not in a dysrhythmia.
Seizures (rare)/agitation: IV benzodiazepines incrementally dosed every 5 minutes to effect.
Hypotension: Give 10 – 20 ml/kg of IV crystalloid, if response is not adequate start noradrenaline ( adrenaline is contraindicated due to paradoxical hypotension from beta 2 mediated vasodilatation). Noradrenaline dose: 0.15mg/kg in 50ml D5W at 1-10ml/hr (0.05 – 0.5 mcg/kg/min).
Reduced GCS: Prompt intubation and ventilation.
Hepatic metabolism to inactive water-soluble metabolites.
Large volume of distribution 10-20 L/kg.
This causes an anticholinergic effect (muscarinic receptors) in overdose and drowsiness (histamine receptor blockade). Olanzapine antagonises the mesolimbic dopamine (D2), serotonin, histamine the muscarninic M1 and peripheral alpha 1 receptors. Olanzapine like queitiapine has a predictable dose-dependent CNS depression. Widely used in Australasia and therefore a fairly common presentation to the emergency department. Olanzapine is a second generation atypical antipsychotic.
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