Debrisoquine oxidation in a Finnish population: the effect of oral contraceptives on the metabolic ratio.

1. The debrisoquine hydroxylation phenotype was assessed in 211 healthy subjects of Finnish Caucasian origin. 2. A bimodal distribution was observed in the urinary debrisoquine/4-hydroxydebrisoquin ratio. Eleven subjects (about 5%) were poor metabolizers of debrisoquine, when a ratio of 12.6 was used as the cut-off point. 3. The mean metabolic ratio of 35 extensive metabolizers taking oral contraceptives was slightly lower than that of extensive metabolizers not taking contraceptives. This indicates that oral contraceptives may change the phenotyping near the metabolic ratio of 12.6. 4. The metabolic ratios were determined in eight subjects using both 4 h and 6 h urine collection times. The metabolic ratios corresponded well with each other indicating the usefulness of the shorter 4 h collection time.