The influence of age and multimorbidity on the pharmacokinetics and metabolism of spironolactone

The pharmacokinetics of the metabolites of spironolactone (canrenone and fluorigenic metabolites) were investigated in 10 geriatric female patients with multimorbidity after a multiple daily oral administration of 100 mg spironolactone under steady state conditions. The concentration determinations were carried out simultaneously with a specific HPLC method and a less specific fluorimetric method. On comparison of the pharmacokinetic parameters with the respective values of a control group of younger healthy female subjects, the serum concentrations in the elderly patients were found to be twice as high. In addition, a statistically significant positive correlation with age was found in the patients for the kinetic parameters investigated. A positive correlation existed between erythrocyte count and the pharmacokinetic parameters of canrenone, especially with the area under the concentration/time curve. No such association was detectable, however, for the total fraction of fluorigenic metabolites (including canrenone). The results of our investigation indicate that, in addition to the known high binding of canrenone to plasma proteins, there is also possibly a (restrictive) binding to erythrocytes.