Generic immunosuppressants.

Immunosuppressive drugs for solid organ transplantation are critical dose drugs with a narrow therapeutic index. Many of the most commonly used innovator drugs are off patent and have been replicated by generic counterparts, often at substantial cost-savings to the patient. However, serious adverse events caused by the transition from innovator to generic medications, specifically in pediatric solid organ transplant recipients, have questioned these autosubstitutions. The purpose of this review is to summarize the criteria set forth by the regulatory bodies, and to examine how major immunosuppressive drugs conform to these recommendations. Regulatory bodies have established inconsistent criteria to demonstrate bioequivalence between innovator and generic medications, causing approved generic variations to have varying levels of equivalence with the innovator drugs. In order to minimize the risk for under-immunosuppression, the following recommendations have been concluded. Brand prescribing of cyclosporine and tacrolimus are recommended due to evidence of adverse events after conversion to generic formulations and differences in dissolution parameters. Mycophenolate mofetil (MMF) shows better bioequivalence between innovator and generic formulations, however caution should be advised when switching between formulations. The institution of 'innovator only' policies may be appropriate at this time in order to minimize the risk of under-immunosuppressing patients until the evidence of more stringent bioequivalence has been established.

Stability of tacrolimus injection diluted in 0.9% sodium chloride injection and stored in Excel bags.

PURPOSE: The chemical stability and physical compatibility of tacrolimus i.v. infusion solutions prepared in Excel bags and stored at 23 or 4 °C for up to nine days were studied. METHODS: Tacrolimus admixtures (2, 4, and 8 µg/mL) were prepared in Excel bags using 0.9% sodium chloride injection and stored at 23 °C without protection from light or at 4 °C in the dark. Test samples were withdrawn from triplicate bag solutions immediately after preparation and at predetermined time intervals (1, 3, 5, 7, and 9 days). Chemical stability was assessed by measuring tacrolimus concentrations using a validated stability-indicating high-performance liquid chromatography assay. The physical stability of the admixtures was assessed by visual examination and by measuring turbidity, particle size, and drug content. RESULTS: All test solutions stored at 23 or 4 °C had a no greater than 6% loss of the initial tacrolimus concentration throughout the nine-day study period. All test samples of tacrolimus admixtures, under both storage conditions, were without precipitation and remained clear initially and throughout the nine-day observation period. Changes in turbidities were minor; measured particulates remained few in number in all samples throughout the study. CONCLUSION: Extemporaneously prepared infusion solutions of tacrolimus 2, 4, and 8 µg/mL in 0.9% sodium chloride injection in Excel bags were chemically and physically stable for at least nine days when stored at room temperature (23 °C) without protection from light and when stored in a refrigerator (4 °C) in the dark.

Favorable outcomes of tacrolimus compared with cyclosporine A for GVHD prophylaxis in HSCT for standard-risk hematological diseases.

Although calcineurin inhibitors (CNIs) with short-term methotrexate (stMTX) constitute standard prophylaxis for graft-versus-host diseases (GVHD) in hematopoietic stem cell transplantations (HSCT), comparative efficacy of cyclosporine A (CsA) and tacrolimus (Tac) still remains unclear. We have altered GVHD prophylaxis for standard-risk hematological malignancies from CsA (target trough level, 500 ng/mL) to Tac (15 ng/mL) both with stMTX in May 2008, enabling us to compare the efficacy of CNIs with little selection biases. The cumulative incidence of acute and chronic GVHD was comparable for CsA and Tac. Among the GVHD low-risk patients who received stem cells from matched sibling donors or cord blood, the Tac arm had a trend for favorable control of grade III-IV acute GVHD (6.7 vs. 30.0 %, p = 0.2), which may contribute to the significantly better overall survival (p = 0.048) and relapse-free survival (p = 0.043) in that group. Inadequate concentration of CNIs in early phase of HSCT affected the cumulative incidence of acute GVHD in the CsA but not in the Tac arm. There were no differences in the GVHD incidence and survival outcomes between CsA and Tac in the GVHD high-risk subgroup. This study underlies the significance of maintaining adequate CsA concentration in standard-risk HSCT.

Analyses of marketplace tacrolimus drug product quality: bioactivity, NMR and LC-MS.

Tacrolimus (FK506) is a potent, narrow therapeutic index, immunosuppressive drug used to avoid organ rejection in patients that have undergone organ transplantation. Recent clinical reports suggested a significant reduction in the tacrolimus concentration/dose ratio in the plasma of liver and kidney recipients when the reference listed drug was substituted with a generic drug. In response to these concerns about switching between tacrolimus from different approved manufacturers during treatment, the FDA initiated purity, potency and quality studies of the innovator and generic tacrolimus products available in the US marketplace. A combination of analytical methods, including mass spectrometry (LC-MS), nuclear magnetic resonance (NMR) and bioactivity assay were developed and validated to assess the quality of tacrolimus. These tests measured the identity, impurities and activity of tacrolimus from active pharmaceutical ingredient (API) sources and with formulated drug product from five different approved manufactures. In addition, some testing was performed on tacrolimus capsules obtained from a non US approved Indian source. The data obtained showed no discernible difference in the impurity profiles and potency between the generic and innovator tacrolimus products.

Standardization of LC-MS for therapeutic drug monitoring of tacrolimus.

BACKGROUND: LC-MS is increasingly used for therapeutic drug monitoring of tacrolimus. A recent summary from an international proficiency-testing scheme demonstrated that the mass spectrometry respondents were the largest method group. However, these methods lack standardization, which may explain the relatively poor interlaboratory agreement for such methods. This study aimed to provide one path toward the standardization of tacrolimus quantification by use of LC-MS. METHODS: A 40-member whole blood tacrolimus proficiency panel was circulated to 7 laboratories, 4 in the US and 3 in Europe, offering routine LC-MS-based quantification of tacrolimus. All laboratories used a common LC-MS platform and followed the manufacturer's instructions that accompanied an LC-MS reagent kit intended for tacrolimus quantification in whole blood samples. Four patient pools were prepared that had sufficient volume to allow comparison with a tacrolimus reference measurement procedure. RESULTS: For the 40-member panel, the standardized MassTrak LC-MS assay demonstrated excellent agreement with a validated LC-MS method used by Analytical Services International (y = 1.02x - 0.02; r = 0.99). The CVs for the pooled patient samples ranged from 2.0% to 5.4%. The mean difference from the reference measurement procedure ranged from 0.4% to 4.4%. CONCLUSIONS: Tacrolimus assay standardization, which must include all facets of the analysis, is necessary to compare patient results between laboratories and to interpret consensus guidelines. LC-MS can provide accurate and precise measurement of tacrolimus between laboratories.

Correlation of thermal analysis and pyrolysis coupled to GC-MS in the characterization of tacrolimus.

In recent years, thermal analysis has assumed major role in the pharmaceutical industry because it can be used to evaluate the stability both in the control of raw materials and the finished product, having employment potential in the development and characterization of new products and assessment processes. Tacrolimus (TCR) is a macrolide lactone with potent immunosuppressive activity. The purpose of this study was to characterize tacrolimus raw material using Thermal analysis and Pyrolysis coupled to Gas chromatography-Mass spectrometry (Pyr-GC-MS). It was analyzed four samples of tacrolimus named TCR A, B, C and D. Thermal analysis experiments was performed in Shimadzu equipment, under nitrogen and synthetic air atmosphere in different heating rate. Pyrolysis analysis was conducted in isothermal conditions of 300°C and 400°C coupled to GC-MS, in which the mass spectrometer was operated in scan mode to detect ions in the range of mass of m/z 25-900. The thermal studies by DSC, DTA and DSC-Photovisual showed desolvation process for all tacrolimus raw materials and TG-dynamical demonstrated two pseudo-polymorphic forms (monohydrate and sesquihydrate) of tacrolimus. It was observed good correlation between the stoichiometric mass losses of the TG-dynamical and identification of product ion in Pyr-GC/MS technique. It was possible to correlate the five pyrolytic product ions with the Ozawa kinetic analysis from the thermal decomposition of TG-dynamical. The thermal studies (DSC, DSC-Photovisual, DTA and TG-dynamical) were applied in the thermal characterization of the raw materials of tacrolimus which showed pseudo-polymorphic forms, which must be monitored by pharmaceutical industry, avoiding future problems in pharmaceutical process, chemical stability and bioavailability of the tacrolimus product.

Evaluation, synthesis and characterization of tacrolimus impurities.

Tacrolimus is an immunosuppressant macrolactam of fermentative origin. By means of HPLC, LC-MS and NMR analyses, coupled with the reference standard synthesis, the main impurities of tacrolimus bulk drug samples were identified and their chemical-physical properties reported. Known ascomycin and tautomers I and II were detected. The correct relative retention time HPLC value of 39,40-dihydro tacrolimus was established. The not described 23,24-anhydro derivative was detected and completely characterized. A full characterization of ascomycin and 39,40-dihydro tacrolimus was also reported.

The need for standardization of tacrolimus assays.

BACKGROUND: Owing to the lack of an internationally recognized tacrolimus reference material and reference method, current LC-MS and immunoassay test methods used to monitor tacrolimus concentrations in whole blood are not standardized. The aim of this study was to assess the need for tacrolimus assay standardization. METHODS: We sent a blinded 40-member whole-blood tacrolimus proficiency panel (0-30 µg/L) to 22 clinical laboratories in 14 countries to be tested by the following assays: Abbott ARCHITECT (n = 17), LC-MS (n = 9), and Siemens Dade Dimension (n = 5). Selected LC-MS laboratories (n = 4) also received a common calibrator set. We compared test results to a validated LC-MS method. Four samples from the proficiency panel were assigned reference values by using exact-matching isotope-dilution mass spectrometr at LGC. RESULTS: The range of CVs observed with the tacrolimus proficiency panel was as follows: LC-MS 11.4%-18.7%, ARCHITECT 3.9%-9.5%, and Siemens Dade 5.0%-48.1%. The range of historical within-site QC CVs obtained with the use of 3 control concentrations were as follows: LC-MS low 3.8%-10.7%, medium 2.0%-9.3%, high 2.3%-9.0%; ARCHITECT low 2.5%-9.5%, medium 2.5%-8.6%, high 2.9%-18.6%; and Siemens/Dade Dimension low 8.7%-23.0%, medium 7.6%-13.2%, high 4.4%-10.4%. Assay bias observed between the 4 LC-MS sites was not corrected by implementation of a common calibrator set. CONCLUSIONS: Tacrolimus assay standardization will be necessary to compare patient results between clinical laboratories. Improved assay accuracy is required to provide optimized drug dosing and consistent care across transplant centers globally.

Physiochemical properties of generic formulations of tacrolimus in Mexico.

Tacrolimus is an important immunosuppressive agent used to prevent allograft rejection after transplantation. Tacrolimus has a narrow therapeutic index; therefore, it is essential that the physicochemical properties of generic formulations be identical to the brand-name formulation, Prograf. In this study, the physicochemical properties of generic tacrolimus formulations were compared with Prograf. The drug dissolution profiles of generic formulations of tacrolimus were different from that of Prograf. Tacrobell and T-Inmun exhibited faster dissolution than Prograf, and Tenacrine, Framebin, and Talgraf showed slower and incomplete drug dissolution, releasing 24% to 51% of tacrolimus within 2 hours. Generic formulations of tacrolimus demonstrated decreased solubility compared with Prograf. The solubility of Prograf was 35.7 microg/mL at 2 hours and 29.5 microg/mL at 24 hours. The solubility of Tenacrine, Framebin, and Talgraf at 2 hours was 5.5, 12.6, and 7.8 microg/mL, respectively, and the solubility decreased to 0.5, 2.3, and 2.1 microg/mL, respectively, at 24 hours. Whereas Prograf demonstrated content uniformity, the content of the generic tacrolimus formulations varied widely. The standard deviation of content for Tenacrine, Tacrobell, and T-Inmun were high at 29.3, 6.9, and 5.6, respectively. Furthermore, the mean percentage of labeled amount of T-Inmun was 84.2% with a relative standard deviation of 6.7% (minimum value; 72.7%; maximum value; 100.7%). These results indicate that generic formulations of tacrolimus tested in this study are not bioequivalent to Prograf, which suggests that their use may be of potential risk to transplant patients.

An HPLC/MS/MS assay for tacrolimus in patient blood samples. Correlation with results of an ELISA assay.

An HPLC/MS/MS assay for tacrolimus in whole blood using FR900520 as an internal standard was validated over the standard curve range of 0.100-10.040 ng ml-1. The calibration curve for tacrolimus in human blood gave a slope of 0.2481, an intercept of 0.007, and a correlation coefficient (r) of 0.9996, with no interference noted from human blood, analyte, or internal standard stock solutions. Use of EDTA or heparin as the preservative in blood resulted in no significant differences. Samples were stable for at least the time required to assay the maximum number of samples that could be placed in the automated system. The limit of sensitivity of the assay was set at the concentration of the lowest nonzero standard tested, i.e., 0.100 ng ml-1. However, validation of the assay to a limit of 0.010 ng ml-1 is currently underway. The within-run and between-run precision and accuracy of the method were determined for four quality control samples. The highest CV was seen at 0.1 ng ml-1 (17.6% within-run and 15.9% between-run), with other CV < 5%. The recovery ranged 79.6-81.3% for tacrolimus over the range 0.3-8.0 ng ml-1 and was 63.10 +/- 1.37% for FR900520. There was a linear correlation (r2 = 0.963) between assay results by HPLC/MS/MS and ELISA in whole blood from atopic dermatitis patients treated with topical tacrolimus ointment. The difference between the means +/- S.D. determined by HPLC/MS/MS (1.22 +/- 1.46 ng ml-1) and ELISA (1.12 +/- 1.29 ng ml-1) was significant by a paired t-test (P < 0.001) Similarly, there was a linear correlation (r2 = 0.841) between assay results by HPLC/MS/MS and IMx in whole blood from solid organ transplant patients treated with tacrolimus. The difference between the means was significantly higher (P < 0.001) for the IMx (15.80 +/- 8.37 ng ml-1) than the HPLC/MS/MS (13.42 +/- 6.87 ng ml-1).

The enhanced immunosuppressive efficacy of newly developed liposomal FK506 in canine liver transplantation.

Local delivery of immunosuppressants to the graft and lymphatic tissue is a potential appraoch to enhance the immunosuppressive efficacy and to alleviate systemic adverse effects simultaneously. By taking advantage of this method, we developed liposomal FK506. Previous pharmacokinetic study of liposomal FK506 indicated increased FK506 levels in the liver and spleen. Because the liver is the site of the allograft in liver transplantation and the spleen is a major lymphoid tissue, we hypothesized that liposomal FK506 would increase immunosuppressive efficacy in liver transplantation. We evaluated this hypothesis in a canine model. Orthotopic liver transplantation was performed using beagle dogs, and the recipients were divided into the following groups: group I, no immunosuppression (n = 5); group II, 0.05 mg/kg/day of FK506 i.v. in a commercially available i.v. formulation for 14 days (n = 5); and group III, 0.05 mg/kg/day of FK506 i.v. in a liposomal formulation for 14 days (n = 5). All recipients in group I died within 2 weeks. Recipients in group II died within 33 days. In contrast, three recipients in group III survived for more than 200 days (P < 0.05 versus group I or group II). In DNA analysis, splenocyte proliferation activity in group III was significantly suppressed in comparison with group II. These results suggest that liposomal FK506 markedly increase the immunosuppressive efficacy of FK506 in liver transplantation. A local immunosuppressive effect in the grafted liver and significant suppression of splenocyte proliferation might contribute to enhancement of the immunosuppressive efficacy of liposomal FK506.

FK506 conversion therapy in pediatric liver transplantation.

The safety and efficacy of conversion to FK506 after failing immunosuppression with cyclosporine was prospectively evaluated in 31 pediatric liver transplant recipients between April 1991 and March 1993. The patients, who ranged in age from 40 days to 14 years, accounted for 28 primary transplantations and 3 retransplantations. The initial immunosuppression regimen consisted of cyclosporine in combination with prednisone. The indications for conversion were acute or chronic rejection refractory to OKT3, Minnesota antilymphocyte globulin, or steroids (13 patients); hypertension (8 patients); inability to reach a therapeutic level of cyclosporine (6 patients); hirsutism (3 patients); and growth retardation (1 patient). After an average follow-up of 10 months (range, 2 to 25 months), 27 (87%) of the patients are alive and have functioning grafts. Of the 13 patients who were converted for refractory rejection, 9 are alive. Six of these 9 patients experienced a complete biochemical reversal of the rejection process within 3 months of conversion; 2 had a partial response to conversion, and 1 patient failed but underwent successful retransplantation. Three of the 4 patients who died did so without showing any improvement. The remaining 18 patients who were converted for various other reasons are alive and have functioning grafts. Of the 8 patients who developed hypertension on cyclosporine and prednisone, 6 experienced a resolution of this problem within 3 months of conversion. Three of the 18 children who underwent rescue therapy for reasons other than refractory rejection experienced rejection episodes after conversion to FK506. Two of these 3 children achieved resolution with either steroid therapy or an increased dosage of FK506, while the third child developed chronic rejection. The side effects of FK506 were generally minor and resolved by lowering the dose. Lymphoproliferative disease developed in 2 patients (6%). The present study suggests that FK506 is a relatively safe and effective rescue therapy for pediatric liver transplant recipients who have failed immunosuppression with cyclosporine. Longer follow-up is needed to assess the effect of FK506 on growth.