Role of the Lipid Emulsion on an Injectable Formulation of Lipophilic KW-3902, a Newly Synthesized Adenosine A1-Receptor Antagonist

KW-3902 (a newly synthesized adenosine A1-receptor antagonist) has potent diuretic and renal protective activities. We investigated the influence of the emulsion formulation on the pharmacokinetics of KW-3902 and its metabolite (M1) in rats using three different formulations, i.e., a lipid emulsion about 130 nm in diameter composed of egg yolk lecithin: soybean oil: oleic acid=1 : 1 : 0.048, a liposome about 100 nm in diameter composed of egg yolk lecithin, and a saline solution containing 1% (v/v) each of dimethyl sulfoxide and 1 n NaOH. There was no significant difference in the pharmacokinetic parameters of KW-3902 (elimination half-life (T1/2), area under the plasma concentration–time curves (AUC0—∞), total body clearance (CL), mean residence time (MRT) and volume of distribution at steady-state (Vdss)) and M1 (Cmax, T1/2, AUC0—∞ and MRT) after injection of these three dosage forms. Moreover, we investigated in vitro the binding of KW-3902 to blood components using these three formulations. KW-3902 was completely partitioned into the blood components regardless of its dosage form. These findings suggested that KW-3902 dissociated rapidly from the lipid emulsion or liposome in blood after injection and showed intrinsic pharmacokinetics of KW-3902 at doses of 0.1 and 1 mg/kg. Thus, the lipid emulsion formulation of KW-3902 was defined as a solvent, which was a vehicle for dissolving the drugs to prepare the injection, at its expected effective doses.