AbstractAimsPotent immunosuppressive effect of tacrolimus has encouraged its topical application for achieving local anti‐inflammatory effect. However, its poor aqueous solubility presents challenges in formulating biocompatible instillations to justify the investigation of liposomes as vehicle for tacrolimus.MethodsAdult female Sprague‐Dawley rats (N = 52) divided into 4 groups were injected with cyclophosphamide (CYP) (200 mg/kg, ip) except for sham (saline injection, ip). Other three groups were instilled with either saline (1 cc, retained for 1 hr), liposome (LP‐ 1 cc) or liposomal encapsulated tacrolimus (LFK‐ 0.2 mg tacrolimus/1 ml LP). Baseline cystometrogram was performed on day 1 and day 3 prior to bladder harvest for histological staining (N = 24) in all groups except sham. In addition, 4‐hr baseline urine on day 1 and day 3 was collected from all groups for urine PGE2 assay and bladder harvested for PGE2 and IL2 assay on day 3 (N = 28). ResultsRats treated with LFK demonstrated suppression of CYP induced inflammatory reaction with reduced EP4 staining and bladder overactivity (intercontraction interval 61.0% decrease in untreated animals) as well as normalized the several fold elevation of IL 2 and PGE2 levels in tissue and urine. CYP induced effects were not suppressed in rats left untreated with tacrolimus.ConclusionsThis is the first report of immunesuppression in bladder by intravesical delivery of tacrolimus using liposomes. LFK significantly inhibited CYP induced inflammatory cystitis through the modulation of IL2, PGE2, and EP4 function. These findings support investigation of local tacrolimus in cases of inflammatory cystitis refractory to conventional therapy. Neurourol. Urodynam. 30:421–427, 2011. © 2010 Wiley‐Liss, Inc.