Therapeutic drug monitoring of eculizumab: Rationale for an individualized dosing schedule.

The annual cost of eculizumab maintenance therapy in paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic-uremic syndrome (aHUS) exceeds $300,000 per patient. A better understanding of eculizumab pharmacokinetics and subsequent individual dose adjustment could reduce this cost. We measured the trough eculizumab concentration in 9 patients with maintenance therapy (aHUS, n = 7; PNH, n = 2) and determined: 1) the intra- and inter-individual variability; 2) the influence of weight on eculizumab pharmacokinetics; and 3) the rate of elimination of eculizumab following discontinuation. A one-compartment model was developed to describe the pharmacokinetics of eculizumab and predicted complement activity by body weight. Trough eculizumab concentrations were >50 µg/mL in 9/9, >100 µg/mL in 8/9, and >300 µg/mL in 5/9 of patients. Intra-individual variability was low but eculizumab concentrations, closely correlated with patient weight (R(2) = 0.66, p = 0.034), varied broadly (55 ± 12 to 733 ± 164 µg/mL). Pharmacokinetic modeling showed that the elimination half-life varied greatly, with an increase from 7.8 d in a patient weighing 100 kg to 19.5 d in a 40 kg patient. We predicted that infusions of 1200 mg could be spaced every 4 or 6 weeks in patients weighing <90 and <70 kg, respectively. In this pilot study, the current recommended use of a fixed eculizumab dose for maintenance therapy is associated with excessively high trough concentrations in many patients. Further prospective larger studies are now required to support an individualized schedule adjusted for patient weight and based on the observed trough serum eculizumab concentration.

An enzyme-linked immunosorbent assay to study bevacizumab pharmacokinetics.

INTRODUCTION: Bevacizumab is an antivascular endothelial growth factor humanized monoclonal antibody used to inhibit angiogenesis in cancer. It displays an important interindividual pharmacokinetic variability, which could explain part of the interindividual differences in clinical response. Therefore, an assay to measure bevacizumab serum concentrations is needed. METHODS: An enzyme-linked immunosorbent assay was developed using microtiter plates sensitised with vascular endothelial growth factor 165, a recombinant form of vascular endothelial growth factor. Lower and upper limits of quantitation as well as limit of detection were determined. Eight calibrators and three quality controls, with concentrations of 5 mg/L, 30 mg/L, and 75 mg/L, were tested on five occasions initially and on five subsequent occasions. Trough and peak serum concentrations of bevacizumab were measured in patients with metastatic colorectal cancer. Bevacizumab concentrations were described using a two-compartment population pharmacokinetic model with first-order constants. RESULTS: Imprecision and accuracy of calibrators and quality controls were 20% or less, except for the zero calibrator. The limit of detection was 0.033 mg/L. Lower and upper limits of quantitation were 5 and 75 mg/L, respectively. A total of 175 blood samples was available for analysis from 16 patients. Median (range) trough and peak concentrations during the treatment were 47.2 (9.6-106.9) mg/L and 159.3 (33.0-327.3) mg/L, respectively. CONCLUSION: This method is rapid, accurate, reproducible, and may be useful for pharmacokinetic and pharmacokinetic-pharmacodynamic studies as well as in therapeutic drug monitoring of bevacizumab.

An enzyme-linked immunosorbent assay for therapeutic drug monitoring of cetuximab.

Cetuximab is an anti-epidermal growth factor receptor monoclonal antibody used in the treatment of colorectal and head and neck cancers. Part of the interindividual differences in response may be explained by interindividual variability in pharmacokinetics. An assay measuring cetuximab serum concentrations is therefore needed. An enzyme-linked immunosorbent assay was developed using microtiter plates sensitized with a recombinant human epidermal growth factor receptor extracellular domain. Lower and upper limits of quantitation and limit of detection were determined. Eight standard calibrators (SCs) and 3 quality controls (QCs), that is, 0.75, 7.5, and 15 mg/L, were tested on 5 occasions on 1 day and on 5 occasions on different days. Trough and peak serum concentrations of cetuximab were measured in 15 patients with metastatic colorectal cancer and 1 patient with undetermined neoplasia undergoing cetuximab-based chemotherapy. Cetuximab concentrations were described using a 2-compartment population pharmacokinetic model. Imprecision and accuracy of SC and QC were < or = 20%, except for the 0 and 0.1 mg/L SC concentrations (< or = 20%). The limit of detection was 0.012 mg/L. Lower and upper limits of quantitation were 0.75 and 15 mg/L, respectively. A total number of 198 blood samples were available from the 16 patients. Median (range) trough and peak concentrations during the treatment were 49.6 (5.8-105.4) and 177.2 (97.5-235) mg/L, respectively. This method is rapid, accurate, and reproducible and may be useful for pharmacokinetic and pharmacokinetic-pharmacodynamic studies, as well as in therapeutic drug monitoring of cetuximab.

Influence of trough serum levels and immunogenicity on long-term outcome of adalimumab therapy in Crohn's disease.

BACKGROUND & AIMS: Adalimumab is an efficacious therapy for active Crohn's disease, but long-term data are scarce. We conducted an observational study to assess the long-term clinical benefit of adalimumab in patients who failed to respond to infliximab, specifically focusing on the influence of trough serum concentration and antibodies against adalimumab on clinical outcome. METHODS: A total of 168 patients with Crohn's disease treated with adalimumab in a tertiary center were included in a prospective follow-up program. Trough serum concentration and antibodies against adalimumab were measured at predefined time points using enzyme-linked immunosorbent assays. RESULTS: A total of 71% and 67% of patients responded by weeks 4 and 12, respectively; among them, 61.5% demonstrated sustained clinical benefit until the end of follow-up (median [interquartile range], 20.4 [11.7-30.0] months). Of the 156 patients receiving maintenance therapy, 102 (65.4%) had to step up to 40 mg weekly and 60 (38.5%) eventually stopped adalimumab therapy mainly due to loss of response. Significantly lower adalimumab trough serum concentrations were measured throughout the follow-up period in patients who discontinued therapy as compared with patients who stayed on adalimumab. Antibodies against adalimumab were present in 9.2% of the patients and affected trough serum concentration. Serious adverse events occurred in 12% of the patients. CONCLUSIONS: Introduction of adalimumab after failure of infliximab therapy resulted in a sustained clinical benefit in two thirds of patients during a median follow-up period of almost 2 years. Discontinuation was directly related to low adalimumab trough serum concentration, which was observed more frequently in patients who developed antibodies against adalimumab.

IgG1 heavy chain-coding gene polymorphism (G1m allotypes) and development of antibodies-to-infliximab.

OBJECTIVE: The chimeric anti-tumor necrosis factor-alpha antibody infliximab is known to induce antibodies-to-infliximab (ATI) in some treated patients. Immunogenicity in murine variable domains is expected; however, constant domains of its human heavy gamma1 chain may also be implicated as it expresses G1m1 and G1m17 allotypes. This allelic form may be immunogenic in patients that are homozygous for the G1m3 allotype commonly expressed in Caucasoid populations. METHODS: As G1m allotypic divergence may explain the presence of ATI or may influence their concentration, a genotyping method was developed and validated to determine antithetical (i.e. mutually exclusive) G1m3 and G1m17 allotypes (amino acid 120 of CH1 according to the international ImMunoGeneTics information system unique numbering) at the IGHG1 gene level (CH1 359g/a nucleotide polymorphism). Two hundred forty-five blood donors and 118 previously described patients suffering from Crohn's disease, treated with infliximab, and having developed ATI in 73 of them, were genotyped. RESULTS: The IGHG1 CH1 359g/a polymorphism does not depart from the Hardy-Weinberg equilibrium in the control population, and allele frequencies were similar in controls and patients. No association was found between the patient G1m allotypes and the presence of ATI or their concentration. It remains possible that anti-Gm1 antibodies are not well detected by the enzyme-linked immunosorbent assays used for ATI detection and/or that the G1m allotypes are minor antigens on IgG1. CONCLUSION: The IGHG1 polymorphism does not seem to play a major role in the induction of ATI. Further analyses will be required to determine whether it is also the case for humanized or fully human antibodies bearing the same G1m allotypes.

Infliximab pharmacokinetics in inflammatory bowel disease patients.

Infliximab, a chimeric monoclonal antibody, has profoundly modified the treatment of several inflammatory diseases, but no satisfactory description of its pharmacokinetics is available. The objective of this study is to describe the pharmacokinetics of infliximab and to explore the sources of its interindividual variability. Thirty-three chronic inflammatory bowel disease patients were studied. Infliximab serum concentrations, obtained during therapeutic drug monitoring, were analyzed using a population approach. Influence of sex, weight, age, concomitant immunosuppressive treatment, and development of antibodies toward infliximab (ATI) on pharmacokinetic parameters was investigated. A two-compartment model with first-order distribution and elimination constants allowed a satisfactory description of infliximab serum concentrations. Mean population distribution and elimination half-lives were 4.3 and 18.5 days, respectively. Weight and sex were found to significantly influence volume of distribution of the central compartment, which increased with weight and was higher in men. Clearance was 2.7 times higher, and elimination half-life was 34% lower in the presence of ATI. In two patients, an increase in infliximab dose or a decrease in dosing interval lead to a decrease in infliximab clearance toward its value in patients without ATI. Infliximab pharmacokinetics are similar to those of other monoclonal antibodies, notably with an elimination half-life of approximately 3 weeks. Both body weight and sex were found to influence infliximab pharmacokinetics, and its clearance increased thrice in the presence of ATI.

An enzyme-linked immunosorbent assay for therapeutic drug monitoring of infliximab.

An enzyme-linked immunosorbent assay (ELISA) measuring serum infliximab concentrations in treated patients was developed. Microtiter plates were sensitized with tumor necrosis factor alpha (TNF-alpha) and saturated with phosphate-buffered saline (PBS) containing 1% bovine serum albumin (BSA). Samples diluted 1:100 in PBS-1% BSA were added and bound infliximab was detected using peroxidase-conjugated goat anti-human immunoglobulin G specific for Fc fragment (HRP-anti hIgG). Reading was performed using an ELISA plate reader. The limit of detection, calculated by assaying 10 replicates of a drug-free serum sample or blank sample and defined as the lowest concentration distinguishable from zero at 2 standard deviations, was 0.014 microg/mL. Each quality control sample was tested on 7 occasions on 1 day and on 5 separate days. The intraday precision indices of the method were (percent coefficients of variation, CV%) 11.7%, 6.2%, and 6.9% for 0.04 microg/mL, 2 microg/mL, and 4.5 microg/mL, respectively. The corresponding bias measures (percent deviation) were -5.5%, -1.9%, and -7.9%, respectively. The between-days precision was 9.8%, 5.3%, and 5.3% for 0.04 microg/mL, 2 microg/mL, and 4.5 microg/mL, respectively. The corresponding bias were +0.3%, -0.3%, and -7.8%, respectively. Lower limit of quantitation and upper limit of quantitation were 0.04 microg/mL and 4.5 microg/mL, respectively. Trough serum concentrations of infliximab were measured in 6 adult patients with various diseases and in 5 pediatric patients with Crohn's disease. For the latter group, samples drawn 1 hour after the end of the infusion and repeated measurements also were available. Data were described using a 1-compartment population pharmacokinetic model. Terminal elimination half-life was 10.9 days. This method is rapid, accurate, and reproducible, and may be useful in therapeutic drug monitoring of infliximab.

Relationship between occupational risk factors and severity markers of systemic sclerosis.

OBJECTIVE: To investigate a potential association between occupational risk factors and severity markers of systemic sclerosis (SSc) defined by diffuse cutaneous extent, pulmonary involvement, and immunologic profile, i.e., presence of antitopoisomerase I antibody (anti-topo I). METHODS: Occupational exposures were assessed in 105 patients with SSc from 1998 to 2002. Exposures to silica dust, welding fumes, solvents, and epoxy resins were investigated. A group of 39 exposed SSc patients and a group of 66 unexposed ones were identified and compared according to severity markers of SSc. The stage of cutaneous extent was defined according to the classification of Leroy, as limited scleroderma (lSSc) or diffuse scleroderma (dSSc). Respiratory status was defined by pulmonary function tests and high resolution computed tomography. Immunological profile was determined by the presence of anti-topo I or anticentromere antibodies (ACA). Statistical relationships between occupational exposures and severity markers of SSc were evaluated using a multiple correspondence analysis and Fisher's exact test. RESULTS: Diffuse scleroderma affected mainly patients exposed during their occupational life to toxic agents. There were significant or close to significant associations between toxic exposure and dSSc (p = 0.06), pulmonary involvement (p = 0.10), and negative ACA (p = 0.03). The most incriminated products seemed to be epoxy resins (p = 0.06), white spirit (p = 0.07), aromatic solvents (p = 0.07), and silica coupled to welding fumes (p = 0.10). CONCLUSION: Our results indicate that occupational toxic factors have an influence on the severity of SSc.