Examples of medications that can elevate theophylline blood levels include ephedrine, allopurinol (Zyloprim), cimetidine (Tagamet), ciprofloxacin (Cipro), clarithromycin (Biaxin), itraconazole (Sporanox), ketoconazole, erythromycin, oral contraceptives, fluvoxamine (Luvox), and propranolol (Inderal).
Theophylline toxicity can cause nausea, vomiting, insomnia, seizures, agitation and life- threatening heart rhythm abnormalities. St. John's Wort, rifampin, and carbamazepine decrease levels of theophylline and potentially its effect by increasing its elimination. Theophylline may decrease levels and the effect of carbamazepine by increasing its elimination. Theophylline is metabolized mainly by the liver and dosages should be reduced in patients with liver dysfunction. On the other hand, theophylline is generally metabolized more rapidly in smokers (both tobacco and marijuana) and higher dosages may be required.
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