Relationship between vitamin B-6 status and elevated pyridoxal kinase levels induced by theophylline therapy in humans

J Nutr. 1990 Nov;120(11):1352-9. doi: 10.1093/jn/120.11.1352.


Theophylline administration to seven healthy male volunteers resulted in a rapid and significant decline in both plasma and erythrocyte pyridoxal-5'-phosphate levels. Total erythrocyte pyridoxal kinase levels increased during 15 wk of theophylline treatment from a mean initial activity of 19.23 +/- 5.03 (mean +/- SD) to 62.64 +/- 11.59 nmol pyridoxal-5'-phosphate formed/(g hemoglobin.h). Although plasma pyridoxal levels remained normal, the threefold increase in total erythrocyte pyridoxal kinase activity levels did not normalize plasma and erythrocyte pyridoxal-5'-phosphate levels. Pyridoxal-5'-phosphate hydrolysis was not affected by theophylline therapy. Increased pyridoxal oxidation was confirmed by elevated urinary 4-pyridoxic acid excretion after 15 wk of theophylline treatment. Mean erythrocyte alanine aminotransferase activity declined by 70%, and aspartate aminotransferase activity declined by 50%, indicating that decreased availability of pyridoxal-5'-phosphate can have widespread metabolic consequences. We conclude that the effect of theophylline on vitamin B-6 metabolism is not transitory and cannot be overcome by elevated intracellular levels of pyridoxal kinase. However, pyridoxine supplementation (10 mg/d for 1 wk) normalized indices of vitamin B-6 status and reversed the downward trend in both alanine aminotransferase and aspartate aminotransferase activity levels.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Homeostasis
  • Humans
  • Male
  • Nutritional Status
  • Pyridoxal Kinase / blood
  • Pyridoxal Kinase / metabolism*
  • Pyridoxal Phosphate / blood*
  • Pyridoxine / metabolism*
  • Theophylline / blood
  • Theophylline / therapeutic use*


  • Pyridoxal Phosphate
  • Theophylline
  • Pyridoxal Kinase
  • Pyridoxine