Seizures are an uncommon manifestation of poisoning even with poisoning with drugs known to be proconvulsant. The most common poisonings leading to seizures (in Australia) are:
In addition, there are a number of other drugs and poisons that often cause seizures:
Cardiotixic effects may also be seen in severe poisonings with the following drugs:
There are also large numbers of other drugs that may lead to seizures as an agonal event by reducing cerebral blood flow. These will not be discussed here.
Features that may help to differentiate between these drugs are:
|Selected Causes of Seizures||Treatment/Comments|
|Tricyclic antidepressants||Usually associated with prolongation of the QRS interval on the ECG. Treat seizures with benzodiazepines; add phenobarbital if needed. Check for hyperthermia in patients with multiple or prolonged seizures.|
|Newer antidepressants||Bupropion and venlafaxine most commonly associated with seizures but all newer drugs have been reported to cause seizures in overdose. Treat with benzodiazepines; add phenobarbital if needed. Check for hyperthermia/serotonin syndrome in patients with multiple or prolonged seizures.|
|Amphetamines/cocaine||Seizures usually accompanied by other manifestations of sympathetic system overstimulation (e.g., hypertension, tachycardia). Check for hyperthermia in patients with multiple or prolonged seizures. Consider possibility of intracranial hemorrhage or ischemic stroke.|
|Isoniazid (INH)||Patients with INH overdose often have lactic acidosis out of proportion to the number and duration of seizures. Treat with benzodiazepines initially; if pyridoxine (vitamin B-6) is available, give at least 5 gm intravenously, and if the dose ingested is known, give a gram equivalent dose of pyridoxine.|
|Carbamazepine||Seizures may occur as a result of overdose (usually only with high blood levels) or may be breakthrough seizures in a patient with underlying epilepsy who has stopped taking a second antiepileptic medication. Consider hemodialysis if seizures are recurrent or the serum level exceeds 40 mg/L.|
|Theophylline||Seizures after acute overdose common if serum levels exceed 90-100 mg/L; may be seen in patients with chronic intoxication at lower levels (e.g., 20-70 mg/L). Acute overdose with level over 90-100 mg/L should be referred for urgent hemodialysis.|
|Organophosphates/carbamates||Typical cholinergic excess (pinpoint pupils, hypersalivation, bronchorrhea, vomiting and diarrhea)|
|Withdrawal from alcohol||Tremor, anxiety, tachycardia, autonomic instability, hallucinations|
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