Impact of chlorpromazine self-association on its apparent binding constants with cyclodextrins: Effect of SBE7-beta-CD on the disposition of chlorpromazine in the rat

Chlorpromazine is an antipsychotic agent with poor aqueous solubility. Complexation with SBE7-beta-CD can aid intravenous delivery through increasing the apparent solubility of chlorpromazine. However, chlorpromazine has also been known to self-associate. This self-association can influence its capacity to interact with other chemical species, such as cyclodextrins. This study aimed to characterise the self-association and cyclodextrin binding properties of chlorpromazine, and the effect on pharmacokinetic parameters in rats when dosed with a SBE7-Beta-CD containing formulation. Pharmacokinetic studies of chlorpromazine in the presence and absence of SBE7-beta-CD were undertaken in rats. The binding constant of SBE7-beta-CD and chlorpromazine was studied by fluorescence and UV-visible spectrophotometry. Urinary excretion of intact chlorpromazine is highly concentration dependent and the variation can be attributed to the self-association of chlorpromezine. The apparent binding constant of chlorpromazine is highest at pharmacologically relevant concentrations, providing an explanation for the significant increase in renal chlorpromazine excretion observed in rats.