THE HALF-LIFE OF XANTHINE DERIVATIVES IS INFLUENCED BY A NUMBER OF KNOWN VARIABLES. IT MAY BE PROLONGED IN PATIENTS WITH LIVER DISEASE, IN PATIENTS WITH CONGESTIVE HEART FAILURE, IN THOSE AFFECTED WITH CHRONIC OBSTRUCTIVE LUNG DISEASE OR CONCOMITANT INFECTIONS, AND IN THOSE PATIENTS TAKING CERTAIN OTHER DRUGS (ERYTHROMYCIN, TROLEANDOMYCIN, LINCOMYCIN AND OTHER ANTIBIOTICS OF THE SAME GROUP, ALLOPURINOL, CIMETIDINE, PROPANOLOL, AND ANTIFLU VACCINE). IN THESE CASES, A LOWER DOSE OF DOXOFYLLINE MAY BE NEEDED.
PHENYTOIN, OTHER ANTICONVULSANTS AND SMOKING MAY CAUSE AN INCREASE IN CLEARANCE WITH A SHORTER MEAN HALF-LIFE: IN THESE CASES HIGHER DOSES OF DOXOFYLLINE MAY BE NEEDED.