BackgroundPer-oral(PO) administration of Tacrolimus(TAC) results in inadequate trough levels in early post-operative period in liver-transplant(LT) recipients who undergo Roux-en-Y hepaticojejunostomy for biliary reconstruction. Sublingual administration(SL) of tacrolimus provides an alternative route in such patients. ObjectiveTo assess feasibility and safety of SL tacrolimus in adult LT-recipients in early post-operative period and to compare therapeutic efficacy of SL administration of tacrolimus vs.PO route. Patients and MethodSingle-centre, retrospective, observational study carried out in adult living donor liver transplant(LDLT) recipients between January 2022 till December 2022. Recipients who underwent Roux-en-Y hepaticojejunostomy for biliary reconstruction, received tacrolimus through SL route till post-operative day(POD)5 as they were kept nil per oral constituted the study group while recipients who underwent duct-to-duct(D-D) anastomosis for biliary reconstruction were allowed orally from POD1 and received PO-tacrolimus were chosen as controls. Feasibility and safety of SL-Tacrolimus was assessed in terms of patient acceptance, need to discontinue SL-Tacrolimus, incidence of local adverse effects and systemic adverse events like neurotoxicity and nephrotoxicity. Therapeutic efficacy was evaluated by comparing median trough levels(TAC level) achieved and incidence of graft rejection between two groups. Results212 patients underwent LT during the study period of which 125 were included(58 in SL-group and 67 in PO-group). Both groups had comparable baseline characteristics. In SL-group, all patients tolerated SL-Tacrolimus well and no local adverse events were observed. Patients with SL-Tacrolimus administration achieved higher median TAC level(ng/ml) vs.PO route(5.85 vs 5(p=0.06)) despite similar median cumulative tacrolimus dose before assessing TAC-level. 50% patients achieved TAC level ≥6ng/ml in SL-group vs. 35.8% in PO-group(p=0.14). Incidence of neurotoxicity, nephrotoxicity and graft rejection during hospital stay were similar in both the groups(p=0.56,0.82 and 0.28 respectively). ConclusionSL-tacrolimus is safe and provides similar trough levels to PO-tacrolimus and may be considered as viable alternative whenever inadequate TAC-levels are anticipated through per-oral route.