Abstract
Creatine is a naturally occurring guanidino compound. It is found in all types of muscle tissues, most of which are present in skeletal muscle and brain. Creatine in its free or phosphrylated forms plays an important role in the regulation and homeostasis of muscle energy metabolism. It appears to increase lean body mass, high-intensity power output and strength in healthy human. Therefore, there has been great interest among both athletes and the scientific community regarding the therapeutic application of creatine and its benefits as a dietary supplement. However, despite such interest, a little attempt has been made to determine solid-state properties and the oral bioavailability of creatine. Currently, creatine is available as a monohydrate or di-creatine citrate salt form.|The aim of this study was to develop a simple and sensitive LC method for the determination of creatine in aqueous solution as wel) as in rat plasma and characterize the solid-state properties of this compound.|Various HPLC methods have been reported for the analysis of creatine. In most cases, reversed-phase ion-pairing HPLC with UV- photometric detection was utilized. However, not a single study was utilized electrochemical detection tor the determination of creatine in aqueous and biological samples. Electrochemical detection not only offers superior sensitivity and limits of detection for non-aromatic compounds when compared to UV detection, but potentially can be canned out with a minimum of sample preparation. Therefore, a simple and sensitive LC method with pulsed electrochemical detection was developed and validated for the quantitation of creatine in aqueous solution as well as in rat plasma. This method was further utilized to study the solid-state properties, the saturated solubility, and vitro dissolution characteristics of various creatine salts.|In order to detennine solid-state properties of creatine monohydrate, samples were subjected to thermal Analyses, Karl-Fisher titrimetry (KFT), scanning electron microscopy (SEM) and variable temperature X-ray powder difffactonietry (VTXRD). The results of this study suggested that commercially available creatine monohydrate dehydrates at about 97-125°C. A phase transition after dehydration was confirmed by X-ray diffraction. This dehydrated phase at a temperature above 230°C undergoes intramolecular cyclization with a loss of an additional mole of water to form creatinine. Creatinine finally melts with decomposition at about 290°C. VTXRD, confirmed that the above solid- state thermal transfonnation was kinetically driven, and occurred within a narrow temperature range. Mass spectrometric (MS) studies further indicated a possible dimerization of creatinine formed during the solid- state transformation. The future direction of this work is to evaluate the oral bioavailability of different creatine salts in an animal model.