THEOPHYLLINE
Although
it has been largely replaced by inhaled β agonists, theo-phylline continues
to be used for the treatment of bronchospasm by some patients with asthma and
bronchitis . A dose of 20–30 tablets can cause serious or fatal poisoning.
Chronic or subacute theophylline poisoning can also occur as a result of
accidental overmedication or use of a drug that interferes with theophylline
metabolism (eg, cimetidine, ciprofloxacin, erythro-mycin;).
In addition to sinus
tachycardia and tremor, vomiting is com-mon after overdose. Hypotension,
tachycardia, hypokalemia, and hyperglycemia may occur, probably owing to β2-adrenergic
activa-tion. The cause of this activation is not fully understood, but the effects
can be ameliorated by β blockers . Cardiac arrhythmias include atrial
tachycardias, premature ventricular contractions, and ventricular tachycardia.
In severe poisoning (eg, acute overdose with serum level > 100 mg/L),
seizures often occur and are usually resistant to common anticonvulsants.
Toxicity may be delayed in onset for many hours after ingestion of
sustained-release tablet formulations.
General supportive
care should be provided. Aggressive gut decontamination should be carried out
using repeated doses of activated charcoal and whole bowel irrigation.
Propranolol or other β blockers (eg, esmolol) are useful antidotes
for β-mediated
hypotension and tachycardia. Phenobarbital is preferred over phenytoin for
convulsions; most anticonvulsants are ineffective. Hemodialysis is indicated
for serum concentrations greater than 100 mg/L and for intractable seizures in
patients with lower levels.
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