[Serum concentrations of the pyridoxal and pyridoxal-5'-phosphate in children during sustained-release theophylline therapy].

This study was undertaken to investigate the effect of sustained-release theophylline preparations on circulating vitamin B6 concentrations in children with asthma. Twenty-six children with asthma were treated with sustained-release theophylline preparations. Serum concentrations of theophylline and vitamin B6 [pyridoxal (PL) and pyridoxal-5'-phosphate (PLP)] were evaluated. The results obtained from this study were as follows: 1) The serum PL was significantly correlated with the duration of theophylline administration (r = -0.42). 2) The serum PL and PLP concentrations were significantly correlated with serum theophylline concentrations (r = -0.47, r = -0.59, respectively). 3) Serum PL and PLP concentrations in children treated for more than 5 weeks were significantly lower than those treated for less than 4 weeks (p < 0.01, p < 0.05, respectively). 4) Serum PL and PLP concentrations in children within theophylline therapeutic ranges (5-15 micrograms/ ml) were significantly lower than those with less than 5 micrograms/ml (p < 0.01, p < 0.01, respectively). These findings suggest that long-term theophylline therapy or serum theophylline concentration within the therapeutic ranges (5-15 micrograms/ml) can depress serum vitamin B6 concentration in children with asthma. Theophylline-induced seizure may be caused by decrease in gamma-aminobutyric acid concentration in the brain result from decrease in vitamin B6 concentration, even if the serum theophylline concentration is within the therapeutic ranges.