Glucose Metabolism in the First 3 Years after Renal Transplantation in Patients Receiving Tacrolimus versus Cyclosporine-Based Immunosuppression

Patients

Patients were eligible to participate in the study if they met the following criteria: age 18 yr or older, recipient of a cadaveric renal allograft, and no known history of clinical diabetes mellitus. All patients gave written informed consent to participate in the study.

Twenty-three white patients were included in the study. Before surgery, they were randomized to a study group by opening a sealed envelope assigning them to the tacrolimus (n = 11) or cyclosporine (n = 12) groups. At the time of transplantation, both groups were comparable in gender, age, transplantation number, body-mass index (BMI), and primary renal disease (Table 1). During the study, their BMI, renal function (Cockcroft-Gault formula), and the use of drugs that might interfere with glucose metabolism (e.g., antihypertensive drugs, oral contraceptives, phenytoin, pentamidine) were monitored.

Immunosuppression

The tacrolimus dosage was 0.3 mg/kg per day orally in 2 doses starting on day 0. The target trough level was initially 10 to 15 ng/ml, and after month 3, the trough level was lowered to 7 to 10 ng/ml. The cyclosporine dosage was 8 mg/kg per day orally in 2 doses starting on day 0. Initially, the target trough level was 100 to 200 ng/ml; after month 3, it was changed to 100 to 150 ng/ml. Both groups received 1 to 2 mg/kg per day azathioprine until month 3, together with 500 mg methylprednisolone on day 0 and 125 mg methylprednisolone on day 1 after transplantation. Thereafter, they were given 20 mg prednisolone, which was tapered to 15 mg at week 2, to 10 mg at week 4, and to 5 mg from week 6 onward. Cyclosporine (Enzyme Multiplied Immune Technique, Dade Behring, Leusden, the Netherlands) and tacrolimus (IMx, Abbott, Hoofddorp, the Netherlands) whole-blood 12-h trough levels were determined. Cumulative doses of tacrolimus or cyclosporine, and of steroids were calculated at every IVGTT.

Rejection was treated with intravenous steroid pulse therapy (0.5 to 1.0 g methylprednisolone on 3 alternate days) and, in the case of steroid resistance, with antithymocyte globulin for 10 d. During antithymocyte globulin administration, daily orally administered prednisolone was continued. At the time of the first dose of antithymocyte globulin, an additional bolus of 25 mg prednisolone was prescribed.

Glucose Metabolism

Glucose metabolism was studied via IVGTT. The tests were performed in the morning after an overnight fast, at week 3, at months 3 and 6, and at years 1, 2, and 3 after renal transplantation. None of the tests was performed during or within 3 wk after rejection treatment. Glucose (0.5 g/kg) was administered intravenously for 2 to 3 min. Blood samples for measurement of whole-blood glucose, C-peptide, and insulin were taken from the opposite arm at t = −15, 0, 5, 10, 15, 20, 30, 40, 50, and 60 min. Insulin sensitivity index (glucose disappearance rate = k_G) was calculated by linear regression from the log-transformed glucose values of t = 10 to 30 min. A k_G value less than 0.8 mmol/L per minute was considered to be abnormal, between 0.8 and 1.2 mmol/L per minute to be indeterminate, and greater than 1.2 mmol/L per minute to be normal (18,19). C-peptide and insulin secretion—both the increment (the secretion response to a glucose load) and the total secretion (basal + increment)—were calculated as area under the curve by use of a linear trapezoidal technique from the serum value at each time point. With the increment, this was done after subtracting the t = 0 value. Insulin resistance was calculated by use of the insulin/glucose ratio and the homeostasis model assessment (HOMA-R; fasting glucose [mmol/L] × fasting insulin [mU/L]/22.5) (20,21).

During hospitalization, urine was examined daily for glucosuria, and at the outpatient clinic, it was examined during every visit. When glucosuria was detected, whole-blood glucose was examined. When no glucosuria was detected, whole-blood glucose was measured initially at least once every week and later at least every 3 mo. When glucose values were abnormal (more than 6.1 mmol/L in the fasting state or more than 7.8 mmol/L in the nonfasting state) for 2 or more different samples and there was no known explanation, such as additional high-dose steroids or infection, PTDM was diagnosed.

A dipstick method was used for the detection of glucosuria. For the measurement of glucose in whole blood, the CX 7 (Beckman Instruments, Palo Alto, CA) was used, and for C-peptide and insulin, the Autodelfia (Wallac, Turku, Finland) was used. In patients who developed PTDM, fasting glucose levels and fructosamine levels were monitored (Unimate 5 FRUC, ABX, Eindhoven, the Netherlands). Normal reference values from our laboratory were 3.1 to 6.1 mmol/L for fasting glucose, 1.0 to 25.0 mU/L for fasting insulin, 0.12 to 1.20 nmol/L for fasting C-peptide levels, and 0.62 to 1.22 mmol/L for fructosamine.

Statistical Analyses

For statistical analysis, SPSS version 9.0 for Windows (SPSS, Inc., Chicago, IL) was used. For analysis of basic characteristics, the appropriate parametric and nonparametric tests were used. Changes in time and differences between patients who received tacrolimus and cyclosporine were evaluated by ANOVA for repeated measures in 2 separate periods: an early period, from week 3 to month 6 (when patients were still recovering from the operation, when catabolism and immobility gradually improved, and when steroid dose and trough levels gradually decreased) and in a more stable later period, from month 6 to year 3. When Mauchly’s sphericity test was statistically significant, results for univariate tests were given after applying the Greenhouse-Geisser epsilon correction. For correlations between parameters, the Spearman rho rank correlation coefficient was used. Correlations between trough level and parameters of glucose metabolism were evaluated for month 6 to year 3 because only in this period would tacrolimus trough levels correlate adequately with the free levels that are responsible for its actions. P < 0.05 was considered statistically significant.

Patients

At week 28, 1 patient in the cyclosporine group was diagnosed as having PTDM. He was therefore excluded from further investigations. In the tacrolimus group, 2 patients with marginal renal function after transplantation because of preexisting abnormalities in their kidney grafts returned to dialysis at month 10 and month 27, respectively; they were therefore unable to complete the study. Two other patients in the tacrolimus group were treated for acute rejection with courses of solumedrol at day 6 and month 3, respectively. Two patients in the cyclosporine group were treated twice for rejection: 1 patient with 2 courses of solumedrol at day 2 and day 12, and the other with a course of solumedrol at day 18 and antithymocyte globulin at day 25.

Table 2 shows BMI and renal function up to the third year after transplantation. There were no significant differences in BMI and renal function between patients who received tacrolimus and patients who received cyclosporine at any time. From week 3 to month 6, BMI increased gradually in patients who received cyclosporine, whereas there was an initial decrease of BMI in patients who received tacrolimus, with a gradual increase thereafter. In both groups, creatinine clearance improved gradually during the first 6 to 12 mo. Table 3 shows the antihypertensive drugs (from which at least β-blockers and diuretics might interfere with glucose metabolism) used at the time of the IVGTT. No one was treated with other drugs known to interfere with glucose metabolism.

Immunosuppression

Table 2 shows trough levels and cumulative doses of steroids and of the calcineurin inhibitor up to the third year after transplantation. Cyclosporine levels gradually decreased from approximately 180 to 120 ng/ml and tacrolimus trough levels from approximately 13 to 8 ng/ml. Median steroid dose was not significantly different for patients who received tacrolimus compared with patients who received cyclosporine at any time. One patient who received cyclosporine needed a very large amount of additional steroids because of rejection, and by mistake, another patient who received cyclosporine received a much smaller dose of steroids than intended at the time of the transplantation.

Hyperglycemia or PTDM

In the first 24 h after transplantation, all patients had hyperglycemia while receiving high doses of steroids (median glucose, 17.8 mmol/L; range, 7.5 to 28.8 mmol/L). After this period, 2 patients who received tacrolimus and 1 who received cyclosporine had hyperglycemia for 7 to 14 d during steroid pulse therapy for acute rejection (maximum glucose 9.7, 21.6, and 22.5 mmol/L, respectively). One of the 2 patients who received tacrolimus also had an abnormal glucose level of 12.9 mmol/L during additional steroid administration because of surgical intervention. Two patients who received cyclosporine also had an abnormal glucose level of 10.1 and 9.0 mmol/L, respectively, during additional steroid administration because of surgical intervention.

One patient who received cyclosporine had 2 abnormal fasting glucose levels of maximum 7.8 mmol/L 28 wk after transplantation. Because there was no obvious cause for his hyperglycemia, PTDM was diagnosed. His treatment consisted only of changes in diet. Thereafter, fasting glucoses ranged from 7.1 to 9.5 mmol/L, with normal fructosamine levels of 1.04 and 1.11 mmol/L up to graft failure at month 18.

All other patients had fasting glucose levels less than 6.1 mmol/L and nonfasting glucose levels less than 7.8 mmol/L.

Glucose Metabolism

Tables 4 and 5 show the median levels and range of basal and stimulated parameters of glucose metabolism. Table 6 shows changes in time, as well as differences between patients who received tacrolimus and those who received cyclosporine.

Correlations between Trough Level and Parameters of Glucose Metabolism

A weak but statistically significant correlation was found between cyclosporine trough level and both total insulin secretion and increment of insulin secretion (r = 0.312, P = 0.039). Otherwise, tacrolimus and cyclosporine trough levels did not correlate significantly with any of the parameters of glucose metabolism investigated.