Theophylline attenuates circulating vitamin B6 levels in children with asthma.

This study was undertaken to investigate the effect of theophylline on circulating vitamin B6 levels in children with asthma. Twenty-six asthmatic children, including 20 patients who were treated with slow-release theophylline and 6 patients not receiving any type of theophylline preparation, were enrolled in this study. Steady state serum theophylline and vitamin B6 [pyridoxal 5'-phosphate (PLP) and pyridoxal (PL)] levels were evaluated in these patients. A depression of serum PLP levels existed in asthmatic children treated with theophylline compared to those not receiving theophylline (5.3 +/- 0.5 vs. 9.0 +/- 1.4 ng/ml, mean +/- SEM; p < 0.05). A significant negative correlation between the serum levels of PLP and theophylline was demonstrated in the subjects of this study (rs = -0.609, p < 0.001). Oral administration of 200 mg of theophylline (TheoDur) to 5 children with asthma significantly depressed serum PLP levels 4 h after the drug intake (p < 0.05), whereas theophylline did not affect serum PL levels. From these results, we conclude that theophylline induces a depression of circulating PLP levels in asthmatic children.