Toxic seizures

Introduction

• Usually generalised and self-limiting
• Any focal seizure activity warrants searching for alternative cause
• Usually easily controlled with benzodiazepines
• Most common toxic causes in Australia
  • Venlafaxine
  • Bupropion
  • Tramadol
  • Amphetamines
  • Often delayed onset as a result of extended release formulations of above
• Also prominent in alcohol and benzo withdrawal

Herald severe intoxication and a grave prognosis

• Chloroquine
• Propranolol
• Salicylates
• Theophylline
• TCA

Complications

• Prolonged seizure activity can lead to irreversible CNS injury
• Secondary hypoxia – CNS injury and susceptibility to dysrhythmias
• Secondary acidosis – Susceptible to dysrhythmias
• Secondary hyperpyrexia – CNS injury
• Secondary rhabdomyolysis – Dehydration, hyperkalaemia and renal failure

Toxicological causes

• Anticonvulsants – Carbamazepine, topiramate
• Antidepressants – Bupropion, citalopram, escitalopram, desvenlafaxine, venlafaxine, TCA
• Antidysrhythmics – Quinine
• Antipsychotics – Atypicals, olanzapine, phenothiazines, quetiapine
• Baclofen
• Isoniazid
• Hypoglycaemic agents– Insulin, sulfonylureas
• Local anaesthetics

Toxicological causes

• Nicotine
• NSAID’s – Mefenamic acid
• Opioids – Dextropropoxyfene, pethidine, propranolol, tramadol
• Salicylates
• Sympathomimetics/amphetamines
• Theophylline
• Withdrawal – Alcohol, benzodiazepines, barbiturates, zopiclone, zolpidem

Management

• Phenytoin contraindicated
• ABC
• Check cardiac rhythm and output
• Bedside BSL
• IV midazolam 5mg
• Consider barbiturates as second-line (thiopentone 3-5mg/kg if intubated)
• Pyridoxine is third-line agent if suspected isoniazid or hydrazide OD
  • Gram for gram to match isoniazid dose or 5g IV (70mg/kg in children up to 5g)

Last Updated on October 13, 2020 by Andrew Crofton