Division of Blood and Marrow Transplantation, Markey Cancer Center, University of Kentucky, Lexington, KY, USA

Correspondence to: Dr G A Hale, St Jude Children's Research Hospital, Department of Hematology-Oncology, 332 North Lauderdale, Memphis, TN 38015, USA

Microangiopathic hemolytic anemia (MAHA) is a well-described complication of stem cell transplantation. Plasmapheresis is one modality utilized as therapy for patients who develop this complication. However, plasmapheresis may alter whole blood levels of certain medications and its effect on tacrolimus in bone marrow transplant patients is unknown. Because tacrolimus has a narrow therapeutic range, the effect of plasmapheresis on whole blood concentrations would be important to know. We report three allogeneic BMT patients who were receiving tacrolimus as acute GVHD therapy while undergoing plasmapheresis for MAHA. Tacrolimus levels seemed unaffected by plasmapheresis in these patients. Bone Marrow Transplantation (2000) 25, 449-451.

tacrolimus; plasmapheresis; pharmacokinetics; GVHD; BMT; microangiopathic hemolytic anemia

Tacrolimus (FK506) has been studied as a prophylactic and therapeutic agent for acute and chronic graft-versus-host disease (GVHD) following hematopoietic stem cell transplantation.^1,2,3 Tacrolimus has a narrow therapeutic range. Sub-therapeutic levels can lead to inadequate therapy for GVHD while elevated levels can cause unacceptable organ toxicity.⁴ Therefore, it is important to be able to anticipate the effect of various interventions so that blood tacrolimus concentrations can be maintained in a therapeutic range. We describe three allogeneic BMT patients who were simultaneously receiving tacrolimus GVHD therapy and plasmapheresis for microangiopathic hemolytic anemia (MAHA) whose tacrolimus levels were unaffected by plasmapheresis.

Materials and methods

MAHA was defined according to published criteria,⁵ and therapy, including plasmapheresis, was instituted. Acute GVHD, proven by tissue biopsies, was staged and graded according to published criteria.⁶ Once the diagnosis of GVHD was established, patients were treated with methylprednisolone 2 mg/kg/day. If unresponsive to steroids, or signs of cyclosporine toxicity developed, cyclosporine was discontinued, and tacrolimus was substituted. We took care to ensure that cyclosporine levels were less than 100 mg/dl prior to initiating tacrolimus therapy at 0.03 mg/kg/day by continuous intravenous infusion. Tacrolimus levels were assayed using a whole blood automated IMx assay (IMx analyzer; Abbot Laboratories, Abbot Park, IL, USA), with a goal of obtaining levels between 6 mg/dl and 12 mg/dl. Tacrolimus infusions were discontinued during the pheresis procedure. Patients were transfused with irradiated, leukocyte-filtered packed red blood cells to maintain hemoglobin greater than 8 gm/dl or hematocrit greater than 24%. Plasmapheresis was performed via a central venous access device using a COBE Spectra machine (Cobe, Lakewood, CO, USA) to exchange two blood volumes, replacing patient plasma with cryo-poor fresh frozen plasma. The three patients are described below and the pertinent laboratory data are listed in Table 1.

Case reports

Patient 1, a 41-year-old white female with recurrent non-Hodgkin's lymphoma, received a T cell-undepleted marrow graft from an HLA-identical sibling. Despite the use of cyclosporine and methotrexate, she developed grade II acute GVHD of the skin and liver on day +20. Due to the development of severe cyclosporine neurotoxicity, tacrolimus therapy was started on day +34 with slow resolution of the neurotoxicity. On day +34, hemodialysis was initiated for acute renal failure and continued every 48 to 72 h until day +59. Plasmapheresis for MAHA was performed on days +35, 37, 40, 44 and 47. Plasmapheresis and hemodialysis were scheduled so that they were not given on the same day. Tacrolimus was discontinued for 96 h starting on day +37 due to excessively high levels. During plasmapheresis, fluconazole and ciprofloxacin were given. Although the MAHA resolved with therapy, the patient died on day +61 of a presumed CNS infection, characterized by mental status deterioration with ring-enhancing lesions of cerebral cortex. Permission for necropsy was denied.

Patient 2, a 36-year-old white female, developed ALL after being treated for breast cancer 1 year earlier. She was transplanted in first remission with a marrow graft from a matched unrelated donor. GVHD prophylaxis included cyclosporine and T lymphocyte depletion of the graft using the murine monoclonal antibody T10 B9 with complement.⁷ She developed grade III acute GVHD of the skin and gastrointestinal tract on day +12. Due to presumed cyclosporine neurotoxicity, tacrolimus was substituted for cyclosporine on day +19. Plasmapheresis for MAHA was performed daily from days +28 to +31 and +42 to +45. During plasmapheresis, diltiazem and phenytoin were administered. The neurotoxicity subsequently resolved. Plasmapheresis was interrupted so that the patient would receive an investigational monoclonal antibody as treatment for refractory GVHD. On day +28, a pre-plasmapheresis tacrolimus level was 14.8 mg/dl and a post-plasmapheresis level was 15 mg/dl. The tacrolimus infusion was discontinued during a plasmapheresis. During her first pheresis course, her tacrolimus blood concentrations and drug dosage remained unchanged. During her second course, her blood tacrolimus levels generally rose to 9.3 ng/ml during daily plasmapheresis while her dosage had been decreased on the first day of pheresis. She eventually died from refractory liver GVHD.

Patient 3, a 7-month-old white female with acute lymphoblastic leukemia (ALL) with t(4;11) involving the 11q23 chromosomal region, was transplanted in first remission. She received a T cell-undepleted marrow graft from a mismatched unrelated donor (5/6) following conditioning with total body irradiation, cytosine arabinoside and cyclophosphamide. Despite cyclosporine GVHD prophylaxis, she developed grade IV acute GVHD of the skin, gastrointestinal tract, and liver on day +16. Because the GVHD was refractory to cyclosporine and high-dose methylprednisolone, cyclosporine was discontinued. Tacrolimus therapy was initiated on day +29. On day +43, plasmapheresis was initiated for MAHA and continued daily until day +51. Hemodialysis was started on day +44 and continued daily until day +58. Beginning on the first day of plasmapheresis, cisapride and amlodipine were administered. During this interval, the patient developed hepatic insufficiency due to worsening liver GVHD with total bilirubin peaking at 16.3 mg/dl. Tacrolimus was not administered from day +45 to day +52; however, stable tacrolimus levels were noted for the initial 48 h, followed by a gradual decline. After 4 days of plasmapheresis, the tacrolimus levels were unchanged despite receiving no new drug for 48 h. The blood levels dropped gradually, and were still therapeutic on the last day of plasmapheresis. The gradual decline was consistent with hepatic elimination in a patient whose tacrolimus had been discontinued. Although the MAHA responded to therapy, she eventually developed respiratory failure requiring intubation. The patient died on day +59 of multi-system organ failure.

Discussion

The pharmacokinetics of tacrolimus has been previously reported in healthy volunteers, and in recipients of solid organ and bone marrow transplants.^8,9,10,11 Tacrolimus is a large molecule that is highly bound to proteins and to erythrocytes. It is extensively metabolized in the liver primarily through the cytochrome P-450 system. Whole blood levels have been used to guide therapy to optimize therapy and minimize toxicity.^12,13,14

Due to its large molecular size, large volume of distribution, and high degree of protein binding, tacrolimus is not efficiently removed by hemodialysis. However, the effect of other manipulations such as plasmapheresis is not well described. Przepiorka et al¹⁵ describe two patients undergoing allogeneic BMT who were receiving tacrolimus by continuous intravenous infusion as GVHD prophylaxis while undergoing plasmapheresis. One patient underwent plasmapheresis with immunoabsorption of plasma on a protein A column. The other patient underwent plasmapheresis, which replaced 1.5 times the plasma volume with colloid and crystalloid. Both patients received tacrolimus by continuous intravenous infusion during the pheresis procedure with no significant change in the mean whole blood tacrolimus concentrations. Similar to the other report, whole blood tacrolimus concentrations were unaffected by plasmapheresis. The three patients in our series were seriously ill with acute GVHD and MAHA; two required hemodialysis. In addition, in our patients who had impaired hepatic function, interruption of the continuous tacrolimus infusion during the plasmapheresis procedure did not affect tacrolimus levels.

The fact that whole blood concentrations of tacrolimus were unaffected by plasmapheresis may be explained by several factors. The tacrolimus molecule is large and highly protein bound, both characteristics that would make it unlikely to be removed by this procedure. Alternatively, tacrolimus may only be present in low plasma concentrations, being concentrated in other compartments of the blood, such as red blood cells.¹⁶

This report demonstrates that whole blood tacrolimus levels are unaffected in BMT patients with acute GVHD who are receiving tacrolimus by continuous intravenous infusion while undergoing plasmapheresis.

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10 Mekki Q, Lee C, Aweeka F et al. Pharmacokinetics of tacrolimus (FK506) in kidney transplant patients. Clin Pharmacol Ther 1995; 53: 238 (Abstr.),

11 Boswell GW, Bekersky I, Fay J et al. Tacrolimus pharmacokinetics in BMT patients. Bone Marrow Transplant 1998; 21: 23-28, MEDLINE

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14 McMaster P, Mirza DI, Ismail T et al. Therapeutic drug monitoring of tacrolimus in clinical transplantation. Ther Drug Monit 1995; 17: 602-605, MEDLINE

15 Przepiorka D, Suzuki J, Ippoliti C et al. Blood tacrolimus concentration unchanged by plasmapheresis. Am J Hosp Pharm 1994; 51: 1708, MEDLINE

16 Jusko WJ, D'Ambrosio R. Monitoring tacrolimus concentrations in plasma and whole blood. Trans Proc 1991; 23: 2732-2735,

Table 1  Patient data: laboratory values for allogeneic BMT patients undergoing plasmapheresis