Disposition of plasma creatinine in non-azotaemic and moderately azotaemic cats

The objectives of this study were to compare assay methods for plasma creatinine (Pl-creat) in cats and to describe the disposition of creatinine and iohexol in 12 healthy and moderately azotaemic cats. Exogenous creatinine and iohexol were injected simultaneously by intravenous bolus, and repeated blood samples were taken to determine the pharmacokinetic parameters of each marker. Pl-creat was assayed by high-performance liquid chromatography (HPLC), Jaffé and enzymatic methods. The enzymatic method was shown to be more reliable than the Jaffé method. Two stereoisomers, exo- and endo-iohexol were identified. The plasma clearance of creatinine (2.3 ± 0.66 ml/min/kg) was significantly higher (P < 0.001) than that of exo-iohexol (1.7 ± 0.40 ml/min/kg). The volume of distribution (447 ± 97 ml/kg) and elimination half-life (181 ± 77 min) of creatinine were also higher (P < 0.001) than those of exo- and endo-iohexol. The estimated daily endogenous production of creatinine was 65 ± 23 mg/kg. None of the pharmacokinetic parameters was changed by the azotaemic status of the animals.