Inverse targeting of drugs to reticuloendothelial system-rich organs by lipid microemulsion emulsified with poloxamer 338

Lipid microemulsions (LM) consisting of soybean oil and lecithin have been studied as a parenteral drug delivery system for site-specific delivery of non-water-soluble drugs. A major obstacle to targeting to non-RES organs or maintaining high concentrations of LM in vasculature is their rapid and extensive uptake by the RES in the liver and spleen. By replacing lecithin with hydrophilic poloxamer 338, it has been possible to avoid the normal deposition of LM in the liver and spleen (inverse targeting). Poloxamer 338-modified LM (PLM) containing ibuprofen octyl ester was intravenously administered to rats. Ibuprofen concentrations in the plasma and various organs were measured to elucidate the effect of inverse targeting to RES and targeting to other tissues in terms of the incorporated drug rather than the drug carrier. It was suggested that PLM can be exploited to direct lipophilic drugs in LM away from RES in the liver and spleen to other targeting tissues such as inflammatory tissues.