Use of sublingual tacrolimus in adults undergoing hematopoietic cell transplant: A pilot study

Introduction: Orally administered tacrolimus is widely used in hematopoietic cell transplant patients, but multiple clinical situations may arise rendering oral administration infeasible. The undesirable sequelae of intravenous administration, including toxicity, challenges with administration and cost call for innovative solutions to conserve existing supply and optimize safety and efficacy of medication delivery. We sought to demonstrate feasibility of sublingual tacrolimus use and estimate a sublingual-to-oral (SL:PO) conversion ratio in the hematopoietic cell transplant setting. Methods: Ten adults undergoing allogeneic hematopoietic cell transplant received tacrolimus 0.04 mg/kg/dose twice daily. Initial doses were given via sublingual route and a steady state trough level was collected after 4 consecutive doses. Participants were then switched to oral tacrolimus, the dose adjusted for a goal trough 8-12ng/mL, and another steady state trough was drawn. Total daily dose was divided by trough concentration for each route to determine the dosing ratio of SL:PO. Results: Median trough level following sublingual administration was 11.3 ng/mL. Three of these were within goal, 3 were low (4.7–6.4 ng/mL) and 4 were elevated (15.9–18.6 ng/mL). Median SL:PO ratio was 1.02. In 5 participants the SL:PO ratio was <1 (range 0.57–0.94) and in 5 the ratio was ≥1 (range 1.10–1.92). No significant barriers or intolerance to sublingual tacrolimus use were noted. Conclusions: Results demonstrate reliable absorption with sublingual tacrolimus use in patients undergoing hematopoietic cell transplant. Sublingual administration may allow for avoidance of the undesirable complications of IV tacrolimus, such as increased toxicities, required hospitalization for continuous infusion, risk of dose conversion and dilution errors and increased cost. Trial Registry name: Use of Sublingual Tacrolimus in Adult Blood and Marrow Transplant Patients, NCT04041219 https://clinicaltrials.gov/ct2/show/NCT04041219?term=NCT04041219&draw=2&rank=1