INTERINDIVIDUAL VARIABILITY OF COUMARIN 7-HYDROXYLATION IN A TURKISH POPULATION

One hundred healthy Turkish Volunteers (70 male, 30 female) aged from 19 to 56 years were given 5 mg coumarin p.o. after an overnight fast. Urine samples were collected before and 2, 4 and 8 h after drug admini stration. The extent and rate of formation of 7-OH-coumarin (7OHC) was determined by the urinary excretion of the metabolite as measured wit h the fluorometric method. On average, 80 % of 7OHC formed was excrete d in 2 h. The total amount of 7OHC formed was 59.8 % (21.5 %) (mean an d SD, n = 100, range 17-100 %) of the given dose. The percentage of 7O HC excreted during the first 2 h compared with the 7OHC excretion at 8 h was a constant and stable individual characteristic for the rate of the formation of 7OHC ('2 h coumarin test'). Although four individual s had relatively slow coumarin test values (34-40 %), no clear-cut pol ymorphism in the rate of 7OHC formation was found. However, 7OHC forma tion was lower in males and in cigarette smokers.