*Purpose: Extended release tacrolimus (LCP-Tac) is a novel once daily formulation with improved pharmacokinetic parameters compared to immediate release tacrolimus (IR-Tac). LCP-Tac use in renal transplant is associated with reduced tremor and decreased dose requirements; minimal data in heart and lung transplant exist. We sought to assess the outcomes of conversion from IR-Tac to LCP-Tac in a cohort of cardiothoracic transplant recipients (CTRs).

*Methods: All CTRs converted from IR-Tac to LCP-Tac from 10/2018-9/2019 were evaluated. Patient demographics, reason for and dose at time of conversion, conversion dose, and dose needed to achieve goal levels were recorded. Tac variability was calculated using coefficient of variability (CV). To normalize dose requirements across LTRs with variable goals, tac level to dose ratios were calculated.

*Results: Conversion occurred in 25 CTRs with a median of 198 days of follow-up. CTRs converted were 61±16 years old, 68% male, and 60% African-American at a median of 184 (IQR 120-1000) days post-transplant. Twelve (48%) were converted due to tremor, 8 (32%) for high dose requirements and 5 (20%) for adherence. Of those converted for tremor, 10/12 (83.3%) reported improvement in baseline tremor. No change in tac CV was seen in the overall cohort, however in those converted for adherence CV numerically decreased post-conversion (37.5% vs. 28.3%, p=0.16). As expected, overall tac dose requirements were decreased by 18.2%, however 4 CTRs required dose increases to maintain adequate troughs. Dose reductions were less pronounced in those converted for high dose requirements (15.4%, IQR 5.5-32.6). Four CTRs were on concurrent systemic azole therapy. No rejection occurred because of conversion.

*Conclusions: Conversion from IR-Tac to LCP-Tac in CTRs was successful in this limited series. Most CTRs converted for tremor saw improvement. Decreases in dose requirements and stable tacrolimus CV were observed in the overall cohort, with potentially less tac variability (CV) in those converted for adherence. Further research is needed to determine the long-term clinical impact of conversion.

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