Effects of drugs on aminophylline elimination in rats.

Effects of phenobarbital, phenytoin, carbamazepine, cimetidine, erythromycin, combination of sulfamethoxazole + trimethoprim (5:1), and rifampicin (rifampin) on the elimination of aminophylline were examined in female rats. Aminophylline was administered i.p. in a dose of 13.33 mg/kg. Blood samples were collected 0.5, 2, 4 and 7 h after the administration of the injection; one measurement was performed from one blood sample. Plasma aminophylline levels were measured by a modified HPLC method. The elimination half-life of the untreated control group (n = 27) was 4.62 h. The pretreatments with drugs examined were carried out by a gastric tube. The half-life of aminophylline after phenobarbital (10 mg/kg, 7 days, n = 29) was 2.09 h; after phenytoin (10 mg/kg, 7 days, n = 29), 2.47 h; after carbamazepine (400 mg/d, 7 days, n = 25), 2.19 h; after cimetidine (in cimetidine-treated group the blood samples were collected 0.5, 4 and 7 h after the aminophylline injection) (40 mg/kg, 7 days, n = 13), 1.77 h; after erythromycin (800 mg/d, 7 days, n = 28), 2.51 h; after the combination of sulfamethoxazole + trimethoprim in ratio of 5:1 (50 mg/kg, 7 days, n = 23), 2.85 h; and after rifampicin (300 mg/kg, 21 days, n = 23), 2.74 h. Sulfamethoxazole presumably interfered with the HPLC examination of aminophylline.(ABSTRACT TRUNCATED AT 250 WORDS)