[A comparative study between urinary metabolites of sustained-release theophylline and theophylline clearance in...

The relationships between changes in urinary metabolites and theophylline clearance were studied in 40 asthmatic children for each steady state phase. Urinary excretion of 1MU, DMU, 3MX increased with age. There were direct correlations between urinary metabolites, while urinary unchanged theophylline decreased and there was an inverse correlation between urinary metabolites. There was a significant correlation between the excretion of unchanged theophylline and 3MX (r = 0.597, p < 0.0001). The values of renal clearance and hepatic clearance also decreased with age. The changes in hepatic clearance were greater than those of renal clearance and showed a low correlation with unchanged theophylline (r = 0.247, p < 0.002), while the changes in renal clearance were high correlation with those of unchanged theophylline in urine. These changes were significant (r = 0.833, p < 0.0001). The changes in theophylline metabolites and its clearance are clinically important because the effective therapeutic range is narrow. Therefore, we concluded that it would be useful to determine the appropriate administration schedule of theophylline considering changes in renal clearance and urinary unchanged theophylline in different age groups.