Abstract

Following the administration of different oral (20, 40, 60 mg) and intravenous (11.6 mg) doses of riboflavin to healthy humans and female patients with liver cirrhosis (oral 40-mg dose), 7 alpha-hydroxyriboflavin (7-hydroxymethylriboflavin) was identified in blood plasma by fluorescence after high-performance liquid and thin-layer chromatographies, and by its absorbance spectrum. The apparent first-order absorption rate constant of 7 alpha-hydroxyriboflavin was 1.2 per hour in healthy subjects. Plasma peak concentrations of 40 nmol/l in males and 20 nmol/l in females (p < 0.01) were achieved within two hours. Peak concentrations and areas under the plasma curves (smaller in females, p < 0.01) of 7 alpha-hydroxyriboflavin were 5 to 16% of those observed for riboflavin. Healthy females showed an approximately 2.5-fold faster disposition of 7 alpha-hydroxyriboflavin from plasma than males (p < 0.01). Correction of peak concentrations and areas under the plasma curves by the rate constants of disposition led to the finding of approximately equal amounts of 7 alpha-hydroxyriboflavin released into plasma by both sexes (p > 0.05). No significant influence of different oral riboflavin doses on 7 alpha-hydroxyriboflavin kinetics was found (p > 0.05). Liver cirrhosis had no significant effect on the amount of 7 alpha-hydroxyriboflavin released into blood plasma (p > 0.05). However, the failure to detect this metabolite following intravenous riboflavin administration indicates a substantial influence of gastrointestinal- or liver-passage.