THE IDENTIFICATION AND KINETICS OF 7-ALPHA-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 int ravenous (11.6 mg) doses of riboflavin to healthy humans and female pa tients with liver cirrhosis (oral 40-mg dose), 7 alpha-hydroxyriboflav in (7-hydroxymethyl-riboflavin) was identified in blood plasma by fluo rescence 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 nmo l/l in females (p<0.01) were achieved within two hours. Peak concentra tions and areas under the plasma curves (smaller in females, p<0.01) o f 7 alpha-hydroxyriboflavin were 5 to 16% of those observed for ribofl avin. Healthy females showed an approximately 2.5-fold faster disposit ion of 7 alpha-hydroxyriboflavin from plasma than males (p<0.01). Corr ection of peak concentrations and areas under the plasma curves by the rate constants of disposition led to the finding of approximately equ al amounts of 7 alpha-hydroxyriboflavin released into plasma by both s exes (p>0.05). No significant influence of different oral riboflavin d oses on 7 alpha-hydroxyriboflavin kinetics was found (p>0.05). Liver c irrhosis had no significant effect on the amount of 7 alpha-hydroxyrib oflavin released into blood plasma (p>0.05). However, the failure to d etect this metabolite following intravenous riboflavin administration indicates a substantial influence of gastrointestinal- or liver-passag e.