The identification and kinetics of 7α-hydroxyriboflavin (7- hydroxymethylriboflavin) in blood plasma from humans following oral administration of riboflavin supplements

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). 7α- hydroxyriboflavin (7- hydroxymethyl-riboflavin) 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 7α-hydroxyriboflavin was 1.2 per hour in healthy subjects. Plasma peak concentrations of 40nmol/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 7α-hydroxyriboflavin were 5 to 16% of those observed for riboflavin. Healthy females showed an approximately 2.5-fold faster disposition of 7α-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 7α-hydroxyriboflavin released into plasma by both sexes (p > 0.05). No significant influence of different oral riboflavin doses on 7α-hydroxyriboflavin kinetics was found (p > 0.05). Liver cirrhosis had no significant effect on the amount of 7α-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.