[Simultaneous determination of exogenous phosphocreatine and its metabolite creatine in rabbit plasma using ion-pair...

A method for simultaneous determination of exogenous phosphocreatine (PCr) and its metabolite creatine (Cr) in rabbit plasma was developed by using an ion-pair reversed-phase high performance liquid chromatography (IP-RP-HPLC). The pharmacokinetics (PK) of PCr was also investigated. In the IP-RP-HPLC method, a Kromasil C,8 column was used with methanol and phosphate buffer containing tetrabutylammonium hydrogen sulfate (TBA, ion-pair reagent) as the mobile phases in a gradient elution mode, while changing detection wavelength and flow rate. The internal standard method was used to quantify PCr and Cr, and the baseline subtraction method was applied. The calibration curves showed good linearity ranged from 10 to 7 500 mg/L for PCr and from 10 to 1 500 mg/L for Cr, and the correlation coefficients (r) were greater than 0. 999. The methodology validation showed high specificity, precision and recovery with the intra-day and inter-day relative standard deviations (RSDs) of not more than 6. 2%, accuracies of 96. 5% - 102. 4%, and extraction recoveries of more than 92%. After intravenous injection of PCr, the concentration-time profile can be best described by two-compartment model with elimination half time of (20.4 +/- 2.7) min, apparent volume of distribution of (0.179 +/- 0.037) L/kg and clearance rate of (0.019 +/- 0. 002) L/(kg x min). The Cr appeared rapidly with time to maximal concentration of 30 min, elimination half time of (43.7 +/- 4. 5) min. The results of practical application showed that this bio-analytical method can completely meet the requirements for PK study of PCr in rabbit plasma.