Predictions of stability in pharmaceutical preparations XIX: Stability evaluation and bioanalysis of clofibric acid esters by high-pressure liquid chromatography.
Specific, sensitive, reversed-phase high-pressure liquid chromatographic assays of clofibric acid esters, clofibrate and etofibrate, and their hydrolysis products, clofibric acid and its monoglycolate and nicotinic acid and its monoglycolate, have been developed in aqueous solution and in biological fluids. Sensitivities of 100 ng/ml of injected mobile phase, a 10-fold increase over existing methods, are reported. Plasma concentrations as low as 200 ng/ml can be analyzed easily in the miscible phase after acetonitrile denaturation. The compounds and their products can be extracted with haloalkane solvents. The extracts were evaporated, reconstituted, and assayed in minimal amounts of mobile phase, resulting in sensitivities of 10 ng/ml of plasma. Conditions are presented that minimize interferences with plasma components. The assay was used to determine the stability of the clofibric acid esters in aqueous solutions, to establish log k-pH profiles at various temperatures, and to evaluate Arrhenius parameters. Hydrolysis was by specific acid-base catalysis. The initial product of etofibrate solvolysis at pH greater than 6 is the monoglycol ester of clofibric acid; at pH less than 3, it is the monoglycol ester of nicotinic acid. Clofibric acid esters are highly unstable to mild alkali (1-3 hr at pH 10 and 30 degrees); even in the estimated pH range of maximum stability, they have half-lives of 100-200 days at 30 degrees. They have half-lives of 4-7 min at 37.5 degrees in fresh dog plasma, and data presented indicate that clofibric acid monoglycolate is an initial product of etofibrate solvolysis.
D000818:Animals; D002021:Buffers; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D002994:Clofibrate / Q000031:analogs & derivatives* / Q000097:blood; D002995:Clofibric Acid / Q000031:analogs & derivatives* / Q000032:analysis / Q000097:blood; D004285:Dogs; D004355:Drug Stability; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D066298:In Vitro Techniques; D007700:Kinetics; D008956:Models, Chemical
D002021:Buffers; C009746:etofibrate; D002995:Clofibric Acid; D002994:Clofibrate