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Specificity of Therapeutic Drug Monitoring of Tacrolimus in Kidney Transplant Patients
Specificity of Therapeutic Drug Monitoring of Tacrolimus in Kidney Transplant Patients S. Sato, S. Fuchinoue, T. Tojimbara, S. Fujita, I. Nakajima, T. Agishi, T. Hayashi, Y. Teramura, E. Fujita, and K. Iwasaki
T
ACROLIMUS (FK 506) is a potent immunosuppressive agent prescribed for the control of rejection in transplant patients. The monitoring of FK 506 levels is one of the important factors for the effective and safe use of FK 506. During therapeutic drug monitoring of the immunosuppressants, blood levels measured should reflect the levels of unchanged drug for the proper evaluation of the levels.1 Therefore, it should be essential to estimate whether the levels during the monitoring would reflect unchanged FK 506 (specific or not) because some metabolites showed immunoreactivity against the monoclonal antibody.2 The goal of this study was to estimate the specificity of values determined by the enzyme immunoassays during therapeutic drug monitoring of FK 506. Fig 2. Concentration of FK 506 between LC/MS and IMx.
MATERIALS AND METHODS Whole blood samples (n 5 30) were collected from 18 kidney transplant patients with dosing postoperative period ranging from 3 days to 19 weeks. Two patients received 24-hour continuous intravenous infusion of FK 506 and the rest of the patients were given oral FK 506. Specific assay for unchanged FK 506 was established by liquid chromatography/electrospray tandem mass spectrometry (LC/MS) (S. Sato, et al, in press). Reagents for LC/MS were obtained from domestic suppliers. The whole blood levels of FK 506 were measured by nonspecific enzyme immunoassays including enzyme-linked immunosorbent assay (ELISA) and microparticle enzyme immunoassay (MEIA, IMx) and compared with those determined by specific high performance LC/MS. Reagents for
Fig 1. Concentration of FK 506 levels between LC/MS and ELISA.
ELISA were obtained as described previously,3 and those for MEIA were purchased from Dainabot Co., Ltd (Tokyo, Japan).
RESULTS AND DISCUSSION
Correlation of FK 506 levels determined by these methods were as follows (Figs 1 and 2): ELISA 5 0.998 LC/MS 2 0.229 (r2 5 0.985); IMx 5 1.135 LC/MS 1 0.978 (r2 5 0.985). The values determined by the nonspecific enzyme immunoassays were almost the same to unchanged FK 506 levels measured by LC/MS and very good correlation of the values between the specific and nonspecific assays were observed. The slopes of two regression lines were close to one and the lines passed through almost the origin of the coordinate. Three of eight metabolites isolated in an in vitro system exhibited equipotent immunoreactivity to unchanged FK 506 against the monoclonal antibody using the enzyme immunoassay.2 The levels of these immunoreactive metabolites were very low or negligible in the whole blood of kidney transplant patients because levels determined by From the Department of of Surgery III, and Clinical Laboratory, Tokyo Women’s Medical College, Tokyo, Japan and Biopharmaceutical and Pharmacokinetic Research Laboratories, Fujisawa Pharmaceutical Co., Ltd., Tokyo, Japan. Address reprint requests to S. Sato, MD, Department of Third Surgery, Tokyo Women’s Medical College, 8-1, Kawada-cho, Shinjuku-ku, Tokyo 162, Japan.
0041-1345/98/$19.00 PII S0041-1345(98)00239-5
© 1998 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
1274
Transplantation Proceedings, 30, 1274–1275 (1998)
SPECIFICITY OF THERAPEUTIC DRUG MONITORING
enzyme immunoassays were very close to those by LC/MS. These results indicate that tacrolimus concentrations determined by the nonspecific enzyme immunoassays (ELISA and IMx) reflect the levels of unchanged FK 506 measured by the specific LC/MS during therapeutic drug monitoring. The concentrations determined by ELISA and IMx are equivalent to those measured by LC/MS.
1275
REFERENCES 1. Tsunoda SM, Aweeka FT: Clin Pharmacokinet 30:107, 1996 2. Iwasaki K, Shirago T, Matsuda H, et al: Drug Metab Disposition 23:28, 1995 3. Iwasaki K. Matsuda H, Shirago T, et al: Xenobiotic Metab Disposition 10:837, 1995
T
ACROLIMUS (FK 506) is a potent immunosuppressive agent prescribed for the control of rejection in transplant patients. The monitoring of FK 506 levels is one of the important factors for the effective and safe use of FK 506. During therapeutic drug monitoring of the immunosuppressants, blood levels measured should reflect the levels of unchanged drug for the proper evaluation of the levels.1 Therefore, it should be essential to estimate whether the levels during the monitoring would reflect unchanged FK 506 (specific or not) because some metabolites showed immunoreactivity against the monoclonal antibody.2 The goal of this study was to estimate the specificity of values determined by the enzyme immunoassays during therapeutic drug monitoring of FK 506. Fig 2. Concentration of FK 506 between LC/MS and IMx.
MATERIALS AND METHODS Whole blood samples (n 5 30) were collected from 18 kidney transplant patients with dosing postoperative period ranging from 3 days to 19 weeks. Two patients received 24-hour continuous intravenous infusion of FK 506 and the rest of the patients were given oral FK 506. Specific assay for unchanged FK 506 was established by liquid chromatography/electrospray tandem mass spectrometry (LC/MS) (S. Sato, et al, in press). Reagents for LC/MS were obtained from domestic suppliers. The whole blood levels of FK 506 were measured by nonspecific enzyme immunoassays including enzyme-linked immunosorbent assay (ELISA) and microparticle enzyme immunoassay (MEIA, IMx) and compared with those determined by specific high performance LC/MS. Reagents for
Fig 1. Concentration of FK 506 levels between LC/MS and ELISA.
ELISA were obtained as described previously,3 and those for MEIA were purchased from Dainabot Co., Ltd (Tokyo, Japan).
RESULTS AND DISCUSSION
Correlation of FK 506 levels determined by these methods were as follows (Figs 1 and 2): ELISA 5 0.998 LC/MS 2 0.229 (r2 5 0.985); IMx 5 1.135 LC/MS 1 0.978 (r2 5 0.985). The values determined by the nonspecific enzyme immunoassays were almost the same to unchanged FK 506 levels measured by LC/MS and very good correlation of the values between the specific and nonspecific assays were observed. The slopes of two regression lines were close to one and the lines passed through almost the origin of the coordinate. Three of eight metabolites isolated in an in vitro system exhibited equipotent immunoreactivity to unchanged FK 506 against the monoclonal antibody using the enzyme immunoassay.2 The levels of these immunoreactive metabolites were very low or negligible in the whole blood of kidney transplant patients because levels determined by From the Department of of Surgery III, and Clinical Laboratory, Tokyo Women’s Medical College, Tokyo, Japan and Biopharmaceutical and Pharmacokinetic Research Laboratories, Fujisawa Pharmaceutical Co., Ltd., Tokyo, Japan. Address reprint requests to S. Sato, MD, Department of Third Surgery, Tokyo Women’s Medical College, 8-1, Kawada-cho, Shinjuku-ku, Tokyo 162, Japan.
0041-1345/98/$19.00 PII S0041-1345(98)00239-5
© 1998 by Elsevier Science Inc. 655 Avenue of the Americas, New York, NY 10010
1274
Transplantation Proceedings, 30, 1274–1275 (1998)
SPECIFICITY OF THERAPEUTIC DRUG MONITORING
enzyme immunoassays were very close to those by LC/MS. These results indicate that tacrolimus concentrations determined by the nonspecific enzyme immunoassays (ELISA and IMx) reflect the levels of unchanged FK 506 measured by the specific LC/MS during therapeutic drug monitoring. The concentrations determined by ELISA and IMx are equivalent to those measured by LC/MS.
1275
REFERENCES 1. Tsunoda SM, Aweeka FT: Clin Pharmacokinet 30:107, 1996 2. Iwasaki K, Shirago T, Matsuda H, et al: Drug Metab Disposition 23:28, 1995 3. Iwasaki K. Matsuda H, Shirago T, et al: Xenobiotic Metab Disposition 10:837, 1995