Sparteine oxidation is practically abolished in quinidine-treated patients

Extensive metabolizers of debrisoquine become poor metabolizers during quinidine treatment

Seven male patients (age 55-75 years) were debrisoquine-tested immediately before and after one week of treatment with quinidine sulphate (200 mg X 3-4 day-1). Before quinidine all patients were classified as extensive metabolizers (metabolic ratio 0.1-3.6). During quinidine the formation of 4-OH-debrisoquine was practically abolished and the phenotype of the patients was altered to PM (metabolic ratio 15-51). This is probably due to an inhibition of debrisoquine hydroxylation by quinidine. Inhibition of 4-OH-debrisoquine formation was associated with a disproportionate increase in debrisoquine excretion.

Sparteine oxidation polymorphism in Greenlanders living in Denmark

Sparteine oxidation appeared to be polymorphic in 185 healthy Greenlanders living in Denmark. Six subjects (3.2%) were phenotyped as poor metabolizers (PM) and 179 subjects as extensive metabolizers (EM). The metabolic ratio (MR) between sparteine and 2- + 5-dehydrosparteine in a 12 h urine sample ranged from 0.06-3.12 in EM and from 30-480 in PM. The excretion of dehydrosparteines accounted for less than 2.2% of the dose in PM and ranged from 5.6%-63% in EM. The urinary recovery (% of dose) of sparteine, 2-dehydrosparteine and total sparteine + dehydrosparteines was lower in Greenlander EM than in Danish EM (Brøsen et al., 1985). Incomplete urine collection in a substantial proportion of the Greenlanders could explain these discrepancies.