Introduction:
Use of Tacrolimus has improved post transplant outcomes by bounds and leaps but one of the main challenges that remains is to achieve target tacrolimus levels post kidney transplant. It widely fluctuates inter individually. Tacrolimus is metabolized by the cytochrome CYP3A enzyme. Individuals Carrying CYP3A5*1 generate functional gene and are called fast metabolizers. Patients carrying CYP3A5*3 are non expressors and are called slow metabolizers. Tacrolimus Genotyping is now an easily available commercial test. Tacrolimus genotype 1*/1* and 1*/3* are fast metabolizers . They are frequently associate with low tacrolimus levels post transplant which can increase kidney rejection rate. The most common solution to improve Tacrolimus level is to increase the tacrolimus dose, but that leads to increase chances of side effects including acute kidney injury and also increases the cost of therapy. Fluconazole inhibits CYP3A enzyme. It has been used clinically to help increase tacrolimus levels in patients who have sub therapeutic tacrolimus levels post surgery. Armed with this knowledge and experience we created a protocol of using Tacrolimus genotyping pre-operatively to identify fast metabolizers and used fluconazole regularly pre operatively to help reach therapeutic Tacrolimus levels in blood post kidney transplant.
Methods:
Tacrolimus genotyping was done pre-operatively in all patients who underwent kidney transplant at our center from Jan 2023 to June 2024 .Patients who did not have results of tacrolimus genotype (June 2022 to January 2023) were included in the comparison arm. Patients were classified as fast metabolizers (Tacrolimus genotype 1*/1* and 1*/3*) and slow metabolizers (tacrolimus genotype 3*/3*). Fast metabolizers were started on tab tacrolimus 0.1mg/kg/day and Tab fluconazole 100mg per day on preop day -3.Slow metabolizers were started on tab tacrolimus at 0.1mg/kg/day on day -3. All patients in standard arm had received Tab tacrolimus at 0.1mg/kg/day started at preop day -3. All patients were given mycophenolate mofetil and steroids. Induction was given as Rabbit thymoglobulin (3mg/kg) as per patient's immunological status. Post operatively patient's tacrolimus levels were measured on POD 0 , POD 3 and POD6.The results were used to adjust tacrolimus doses to target a level of 8-12ng/ml. Kidney function test was measured daily. Patients with slow graft function underwent kidney biopsy.
Results:
Total of 62 patients were transplanted at our Centre from June 2022 to June 2024. Tacrolimus genotype was done for all patients who were transplanted between January 2023 to June 2024 (n=46). Fast metabolizers (Tacrolimus Genotype 1*/1* and 1*/3*) were 21 (45.7%) and slow metabolizers (genotype 3*/3*) were 25( 54.3%). 16 patients were transplanted between June to December 2022, and no genotype reports were available for them. They were used as standard arm against which comparative analysis was done.
Of the 62 patients, Male were 56.5% and females were 43.5%. Patients more than 40 year were 60% with mean age of group was 44.79years(18 – 70yrs). A Positive blood group was present in 29% of recipients, B positive in 24%, 0 positive in 34% and AB positive in 13% patients. Hypertension was the most common comorbidity, seen in 96.8% followed by diabetes Mellitus which was seen in 37%. Coronary Artery Disease was seen in 11.5% recipients. 2 (3.6%) patients were hepatitis B positive and 2 (3.6%)patients were positive for hepatitis c virus .
All patients received Tacrolimus, mycophenolate mofetil and steroid as maintenance immunosuppression. Rabbit thymoglobulin (1.5 to 3 mg/kg ) induction was used in 96% patients. Tacrolimus was started on day minus 3 from operative day at a dose of 0.1mg/kg/day along with mycophenolate mofetil. In fast metabolizers (genotype 1*/*1 and 1*/3*) additionally fluconazole was added on day minus 3 at standard dose of 100mg/day. Tacrolimus levels were noted on the morning of transplant surgery (POD 0) and then again at Post operative day 3( POD 3) and post operative day 6 (POD 6). The dose of tacrolimus was adjusted as per Tacrolimus level reports. The average Tacrolimus levels on POD 0 was 11.8±3 6.4ng/ml; on POD 3 was 14.4 ±6.8ng/ml and POD 6 was 12.62 ±4.8ng/ml .
The standard arm (n=16) were patients without tacrolimus genotype report. On POD 0 , 25% patients reached target tacrolimus level which improved to 31.25% on POD 3.Among Slow metabolizers, 32% patients had achieved target Tacrolimus levels on POD 0 and POD 3. Fast metabolizers, all of whom were given fluconazole, 19 % patients had achieved target tacrolimus dose of 8 to 12ng/ml on POD 0 which increased to 52% on POD 3. (P<0.05) . In slow metabolizers, the average dose of tacrolimus required to reach target levels was 0.095mg/kg. Comparatively with the use of fluconazole , the dose required in fast metabolizers was only 0.12mg/kg/day. Studies in literature have shown fast metabolizers to need 1.5 to 2 times the dose of slow metabolizers. This is especially significant in countries where patients bear the cost of treatment out of pocket.
Compared to standard arm, fast metabolizers who were given fluconazole had lesser number of patients on POD3 with suboptimal tacrolimus levels (<8ng/ml). Standard arm vs fast metabolizers was 14% vs 25%.Use of fluconazole was not associate with Tacrolimus toxicity(>12ng/ml). The percentage of patients with serum tacrolimus levels more than 12ng/ml in standard arm vs fast metabolizer vs slow metabolizer was significantly different at 43% vs 33% vs 60%. (p <0.05)
There was no difference in mean serum creatinine or rejection rate between the three groups. The mean serum creatinine on discharge (7th day) in standard arm vs fast metabolizer vs slow metabolizer was 0.88± 0.19mg/dl vs 0.86 ±0.2mg/dl vs 0.87±0.27 mg/dl (p =0.865). Only 1 patient in the fast metabolizer group developed acute Antibody mediated rejection requiring plasmapheresis. There was no increase in infection rate including fungal infection between the three groups (p=0.372).
Conclusions:
Doing Tacrolimus genotype testing pre kidney transplant surgery can significantly improve transplant immunosuppression planning as fast metabolizers account for 45.7% patients in our region .Use of low dose fluconazole (100mg/day ) is an effective method in achieving therapeutic tacrolimus levels in early post operative period without increasing risk of tacrolimus toxicity.
I have no potential conflict of interest to disclose.
I did not use generative AI and AI-assisted technologies in the writing process.