Chlorpropamide metabolism

Metabolic-Hydroxy and Carboxy Functionalization of Alkyl Moieties in Drug Molecules: Prediction of Structure Influence and Pharmacologic Activity

Alkyl moieties-open chain or cyclic, linear, or branched-are common in drug molecules. The hydrophobicity of alkyl moieties in drug molecules is modified by metabolic hydroxy functionalization via free-radical intermediates to give primary, secondary, or tertiary alcohols depending on the class of the substrate carbon. The hydroxymethyl groups resulting from the functionalization of methyl groups are mostly oxidized further to carboxyl groups to give carboxy metabolites. As observed from the surveyed cases in this review, hydroxy functionalization leads to loss, attenuation, or retention of pharmacologic activity with respect to the parent drug. On the other hand, carboxy functionalization leads to a loss of activity with the exception of only a few cases in which activity is retained. The exceptions are those groups in which the carboxy functionalization occurs at a position distant from a well-defined primary pharmacophore. Some hydroxy metabolites, which are equiactive with their parent drugs, have been developed into ester prodrugs while carboxy metabolites, which are equiactive to their parent drugs, have been developed into drugs as per se. In this review, we present and discuss the above state of affairs for a variety of drug classes, using selected drug members to show the effect on pharmacologic activity as well as dependence of the metabolic change on drug molecular structure. The review provides a basis for informed predictions of (i) structural features required for metabolic hydroxy and carboxy functionalization of alkyl moieties in existing or planned small drug molecules, and (ii) pharmacologic activity of the metabolites resulting from hydroxy and/or carboxy functionalization of alkyl moieties.

Pharmacokinetics of chlorpropamide in epileptic patients: effects of enzyme induction and urine pH on chlorpropamide elimination

The effects of liver enzyme induction and of urine pH on the pharmacokinetics of chlorpropamide have been studied. A single oral dose of chlorpropamide 250 mg was administered to 8 patients on antiepileptic drugs (phenytoin, carbamazepine) and to 8 healthy volunteers. The half-life of chlorpropamide was significantly shorter in the patients (34.4 h) than in the healthy volunteers (50.2 h), but the difference between the groups in the half-life of antipyrine was even more pronounced (5.1 vs 11.4 h). The clearance and volume of distribution of total chlorpropamide were significantly higher in the patients (2.99 ml X h-1 X kg-1 and 126 ml X kg-1) than in the healthy volunteers (1.60 ml X h-1 X kg-1 and 106 ml X kg-1). The unbound fraction of chlorpropamide in serum was also higher in the patients (5.7%) than in the healthy subjects (4.4%). Neither the volume of distribution nor the clearance of the free fraction of chlorpropamide differed significantly between the groups. There was a significant correlation between the half-lives of chlorpropamide and antipyrine, and the half-life of chlorpropamide also had at least as good an inverse correlation with the urinary excretion of unchanged chlorpropamide. The renal clearance of chlorpropamide correlated well with urine pH and was almost 100-fold higher at pH 7 than at pH 5. Both the metabolic and renal clearances of chlorpropamide are important in its elimination. At urine pH higher than 6.5-7, the renal clearance of chlorpropamide represents more than half its total clearance regardless the degree of induction of liver enzymes.