Toxicology Flashcards
Paracetamol - massive ingestion
> 30g
Phenytoin toxicity features
Neurological signs and symptoms predominate
- cerebellar dysfunction
- ataxia
- tremor
- involuntary movements
Cardiovascular effects are not associated with overdose at any dose of phenytoin.
Hypotension and arrythmia may be features of rapid administration of IV loading of phenytoin in status epilepticus.
Hunter Toxicity Criteria Decision Rule
Ingestion of serotonergic agent plus at least one of:
- spontaneous clonus
- inducible clonus AND (agitation or diaphoresis)
- ocular clonus AND (agitation or diaphoresis)
- tremor AND hyperreflexia
- hypertonia AND temp > 38dC AND (ocular clonus or inducible clonus)
Serotonin syndrome treatment
- Diazepam 0.1 - 0.3mg/kg for gentle sedation
ANTIDOTE
cyproheptadine 8mg PO
alternatives
olanzapine, chlorpromazine
Neuroleptic malignant syndrome Features
- neuromuscular rigidity
- altered mental status
- autonomic instability
- -> IN A PATIENT TAKING NEUROLEPTIC MEDS
CK elevation prominent
CNS
- confusion, delirium, stupor, coma
ANS
- hyperthermia, tachycardia, HTN, resp irregularities, cardiac dysrhythmias
Neuromuscular
- lead pipe rigidity, bradykinesia/akinesia, mutism, staring, abnormal involuntary movements
Neuroleptic malignant syndrome treatment
Bromocriptine (dopamine agonist)
Dantrolene
ECT
Anticholinergic syndrome treatment
Benzos for agitation
Avoid anticholinergic drugs eg olanzapine, droperidol
Antidote = physostigmine
Isoniazid
> 1.5g = symptoms
3g = seizures
10g = fatal
FEATURES
- photophobia
- mydriasis, ataxia
- hyperreflexia
- N&V
- confusion
- status seizures
INVESTIGATIONS
- severe HAGMA, pH 6.8 - 7.3
- high lactate
MANAGEMENT
- aggressive supportive care
ANTIDOTE
- Pyridoxine 5g if coma or seizures
NAC infusion
- 150mg/kg in 200mL over 15 mins
- 50mg/kg in 500mL over 4 hours
- 100mg/kg in 1000mL over 16 hours
(Dextrose 5%)
Salicylate toxic ingestion levels
< 150mg/kg = asymptomatic
> 300mg/kg = severe
> 500mg/kg = potentially lethal
Urinary alkalinisation
1-2mmol/kg NaHCO3 bolus, then IV infusion
target urine pH > 7.5
**Monitor serum K+ for hypokalaemia
Indications for DigiFab
- cardiac arrest
- life-threatening cardiac dysrhythmia
- ingestion > 10mg adult or > 4mg child
- serum level > 15nmol/ml
- serum K > 5mmol/L
HOW MUCH?
- 2 if chronic toxicity (observe response)
- acute and stable = 5
- acute and unstable = 10
- cardiac arrest = 20
Treatment of lead toxicity
Chelation therapy
Sodium calcium edetate (EDTA)
Succimer - oral chelator
Iron - toxic ingestion levels
60-120mg/kg = systemic toxicity
> 120mg/kg = lethal
Iron toxicity - features
0-6 hours = GI upset, hypovolaemia
6-12 hours = pretty ok
12-48 hours = vasodilatory shock, HAGMA, hepatorenal failure
2-5 days = acute hepatic failure
2-6 weeks = cirrhotic liver disease, fibrosis
Iron toxicity - treatment
Early priority = restore circulating volume
Decontamination
- Whole bowel irrigation if:
1. > 60mg/kg ingested
2. confirmed on XR - surgical or endoscopic retrieval if above indicated but impractical
Antidote
- desferrioxamine chelation therapy
Indications for desferrioxamine chelation
- systemic toxicity (shock, HAGMA, etc)
- level > 90micromol/L at 4-6 hours
DOSE = 15mg/kg/hr
What is Fluorosis?
Systemic toxicity from hydrofluoric acid exposure
- hypocalcaemia and hypomagnesaemia –> tetany and prolonged QT
- ventricular dysrhythmias and arrest
ECG prognostication in TCA overdose
QRS > 100 –> seizures
QRS > 160 –> VT
Treatment in TCA overdose
- intubation and HYPERVENTILATION (pH 7.5 - 7.55)
- NaHCO3- 100mmol (2mmol/kg) IV every 1-2 mins until perfusing rhythm restored
- lignocaine 1-1.5mg/kg when pH >7.5 if ongoing ventricular dysrhythmia
- fluids and vasopressors for hypotension
NB - procainamide, amiodarone, B blockers contraindicated
Na channel toxicity: ECG features
tachycardia
prolonged/wide QRS interval
large terminal R in aVR and V1
increased R/S ratio > 0.7 in aVR
QT prolongation secondary to K+ blockade
right axis
Treatment of local anaesthetic toxicity
Intravenous lipid emulsion
1-1.5ml/kg bolus, repeat 2-3x
0.25ml/kg/min IVI max 8ml/kg/min
Treatment of methaemoglobinaemia
Methylene Blue
- if MetHb > 20% and symptomatic
1-2ml/kg slow push
usually a single dose
Associated with benzocaine, lignocaine, prilocaine. More likely in kids. Not dose-related.
Cyanide antidote
Hydroxocobalamin (B12)
2.5g (1 ampuole) over 15 mins
