Captopril methylation in human liver and kidney: Interindividual variability

1. The methylation of captopril was studied in the microsomal fraction obtained from 87 specimens of human liver and 70 specimens of human renal cortex. 2. The rate of captopril methylation ranged over one order of magnitude in the liver and kidney. In the human liver, the mean (+/-SD) rate of captopril methylation (pmol/min/mg) was significantly (p < 0.001) greater in women (199+/-97) than in men (126+/-88), whereas in the kidney no sex-difference was observed, and the mean (+/-SD) of all cases was 47+/-23 pmol/min/mg. 3. In the kidney, the statistical analysis revealed the presence of two subgroups in the rate of captopril methylation and their mean (+/-SD) estimates were 42.5+/-13.9 and 90.3+/-12.0 pmol/min/mg (p < 0.05). Of the population, 84% fell in the former and the remaining 16% in the latter subgroup. 4. Captopril is mainly eliminated by metabolism and its bioavailability is 65%. Methylation is one of the metabolic routes of captopril and its variability may contribute, to some extent, to modulate the intracellular concentration of this drug.