Abstract
Plasma concentration, urinary excretion of theophylline and sodium excretion were investigated in 4 healthy adult volunteers after a single oral dose of 300mg theophylline in a solution form and in sustained-release tablets (Theodur). On the average plasma level curve for Theodur tablets, the peak level was reduced from 10μg/ml to 7μg/ml compared with that of an oral solution, but the prolonged effect for plasma level was observed and the absorption from dosage form was reliable.The renal clearance of theophylline increased initially after a single dose due to its urine flow rate dependence and after a single dose in a solution form the increase in urine flow rate was higher, thereby the initial increase in renal clearance became larger compared with those of sustained-release tablets.Furthermore, the urinary sodium excretion rate after a single dose increased as sigmoidshaped relationship with increasing the renal clearance of theophylline. And the natriuretic effect for oral solution was relatively potent, whereas that for sustained-release tablets appeared to be very weak.
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