Drug-Drug

• Additive CV and CNS side effects with adrenergics (sympathomimetic) .

• May ↓ the therapeutic effect of lithium and phenytoin .

• Smoking, barbiturates , carbamazepine , phenytoin , nevirapine and rifampin may ↑ metabolism and may decrease effectiveness.

• Erythromycin , beta blockers , clarithromycin , calcium channel blockerscimetidine , hormonal contraceptives , disulfiram , doxycycline , estrogens , fluvoxamine , isoniazid , ketoconazole , mexiletine , nefazodone , protease inhibitors , quinidine , some fluoroquinolones , and large doses of allopurinol ↓ metabolism and may lead to toxicity.

Drug-Natural Products

• Caffeine-containing herbs ( cola nut , guarana , mate , tea, coffee) may ↑ serum levels and risk of CNS and CV side effects.

• ↓ serum levels and effectiveness with St. John's wort .

Drug-Food
Excessive regular intake of charcoal-broiled foods may ↓ effectiveness.