Measurement of clofibric acid (CPIB) metabolites in plasma of patients on clofibrate therapy.

1. The metabolites of clofibric acid [CPIB;2-(chlorophenoxy)-2-methylpropionic acid] are present in the plasma of patients on clofibrate therapy. The highest plasma concentrations of CPIB in metabolite form (up to 51 micrograms/ml) were generally found in patients with renal disease. Negligible concentrations (less than or equal to 2 micrograms/ml) were found in only seven patients out of thirty-six studied. 2. The two conjugates of CPIB found in urine were present in plasma. 3. When measuring conjugated CPIB in plasma it is essential to take care in the handling and storage of specimens, and to select an assay method known to be specific for unmetabolized CPIB.