The pharmacokinetics of water‐in‐oil‐in‐water‐type multiple emulsion of a new tacrolimus formulation

We developed a water‐in‐oil‐in‐water (W/O/W)‐type multiple emulsion of a new tacrolimus formulation. A potential approach to avoid the complications of systemic immunosuppression and simultaneously enhance immunosuppressive efficacy is to deliver immunosuppressive agents locally to the site of the target organs. The W/O/W emulsion is dispersed oil drops containing smaller water droplets that allow the delivery of drugs preferentially to the reticuloendothelial system (RES). Since the liver and the spleen are primary components of the RES, and the brain and the kidney have a poor RES, we hypothesized that a W/O/W emulsion of tacrolimus would prossess the pharmacokinetic benefits of local immunosuppression. We evaluated this hypothesis in a rat model. The tacrolimus levels of whole blood, the liver, spleen, brain, and kidney in rats given intravenous emulsions of tacrolimus (W/O/W group) were compared with a group administered tacrolimus alone (T group). There were no significant differences between the pharmacokinetic parameters of W/O/W group and T group based on whole blood data. However, the W/O/W group had significantly decreased tacrolimus levels in the brain and kidney, and significantly increased levels in the liver and spleen compared with the T group. These data suggest that the W/O/W emulsion is applicable as an intravenous drug carrier for local immunosuppression.