Formulation and evaluation of analgesic activity of polysorbate 80-coated loperamide liposomes in mice

Purpose: To deliver loperamide (Lp) into mice brain using polysorbate 80 (PS80)-coated liposomes that inhibits P-glycoprotein (P-gp) efflux.Method: Lp loaded liposomes were prepared by reverse phase evaporation technique using lecithin (Lec) and cholesterol (Ch). The efficacy of PS80-coated Lp liposomes (PLs) in mice was evaluated using central analgesic models (Eddy’s hot plate method and tail immersion test) and peripheral analgesic model (acetic acid-induced writhing).Results: PLs showed maximum possible response (MPR) of 58.33 % at 60 min in Eddy’s hot plate study. In the tail immersion test, PLs showed MPR of 67.64 and 69.24 % at 60 and 90 min, respectively, relative to control group. This confirms the potential of PLs to deliver Lp to the brain by inhibiting P-gp efflux. Dose response study using tail flick method confirmed the minimum Lp dose (25 μg/kg, i.v) required to achieve central analgesic activity using PLs.Conclusion: PS80-coated Lp loaded liposomes (PLs) possess a good potential to inhibit P-gp efflux of Lp from brain, and also exhibit both central and peripheral analgesic activity.Keywords: Loperamide, Polysorbate 80, P-glycoprotein (P-gp), Analgesic activity