Patients w/ HTN, heart disease, hypoxemia, hyperthyroidism, chronic right ventricular failure, CHF, liver disease, renal disease, history of peptic ulcer & in the elderly. t
1/2 may be prolonged in patients w/ liver disease, CHF, chronic obstructive lung disease, concomitant infections or in those taking certain other drugs (erythromycin, troleandomycin, lincomycin & other antibiotics of the same group, allopurinol, cimetidine, propranolol & anti-flu vaccine). Clearance may be increased w/ phenytoin, other anticonvulsants & smoking. Perform lab monitoring of plasma conc in all situations. Pregnancy.