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PHARMACOKINETICS |
From Amgen Inc, Thousand Oaks, California.
Address for reprints: John T. Sullivan, MBChB, Amgen Inc, One Amgen Center Drive, Mailstop 38-4-C, Thousand Oaks, CA, 91320; e-mail: jtsulliv{at}amgen.com.
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Key Words: Arthritis • rheumatoid • receptors • tumor necrosis factor • bioequivalence • pharmacokinetics • etanercept
) is approximately 3 to 4 days.4 The absolute bioavailability of subcutaneous etanercept is reported as 58%.3 Etanercept is currently approved for reducing signs and symptoms, inhibiting the progression of structural damage, and improving physical function in patients with rheumatoid arthritis. It is also approved for reducing the signs and symptoms and inhibiting the progression of structural damage in patients with psoriatic arthritis and for reducing the signs and symptoms of active ankylosing spondylitis, juvenile rheumatoid arthritis, and psoriasis. The recommended dose for adult patients with rheumatoid arthritis, ankylosing spondylitis, and psoriatic arthritis is 50 mg once weekly. It is recommended that adult patients with psoriasis initiate treatment with 50 mg twice weekly for 3 months, followed by a reduction to a maintenance dose of 50 mg once weekly. In patients with rheumatoid arthritis, the safety and efficacy of a 50-mg dose of etanercept (administered subcutaneously once weekly as two 25-mg injections) were found to be comparable to the safety and efficacy of separate 25-mg injections administered 3 to 4 days apart.5 Etanercept was initially approved for rheumatoid arthritis at a dose of 25 mg given twice weekly, but it is now more commonly given as a once-weekly dose of 50 mg.
Etanercept was originally introduced commercially in vials containing 25 mg lyophilized powder requiring reconstitution, and to date most patients have received the reconstituted formulation. A 50-mg/mL liquid formulation supplied in a prefilled syringe was approved recently for commercial use. In this report, we present the results of a study in healthy volunteers comparing the pharmacokinetics of the liquid etanercept formulation with that of the reconstituted formulation.
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Subjects
All subjects gave written, informed consent before any study-related screening procedures were performed. Male and nonpregnant, nonlactating female subjects had to be between the ages of 19 and 55 years and had to have a body mass index between 18 and 31 kg/m2 at the time of screening. Subjects had to be free of any significant and active disease requiring a physician's care and had to test negative for human immunodeficiency virus antibody, hepatitis B surface antigen, and hepatitis C antibody.
Subjects were excluded from the study for any of the following reasons: clinically significant abnormalities in serum chemistry, hematology, or urinalysis values; active infection; history of tuberculosis; hypersensitivity to etanercept or any excipients; use of any prescription or over-the-counter medication within 8 days before the start of the study (except vitamins, topical medications, herbal products, contraceptives, or hormonal replacement therapy) or an investigational agent within 30 days before screening; alcohol consumption within 48 hours before dosing; or history of drug or alcohol abuse within 1 year before screening. Subjects who donated blood products within 12 weeks or a total blood volume of 1500 mL within 1 year before the study and subjects who smoked more than 10 cigarettes per day within 12 months before the study were also excluded.
Treatment
Lyophilized etanercept was supplied as a sterile, preservative-free powder and was administered after reconstitution with 1.0 mL bacteriostatic water for injection (BWFI), United States Pharmacopeia, containing 0.9% benzyl alcohol. The reconstituted solution contained 25 mg etanercept (25 mg/mL). Liquid etanercept was supplied in 1-mL prefilled glass syringes as a sterile protein solution containing 50 mg/mL etanercept, 25 mM sodium phosphate, 25-mM L-arginine, 1% sucrose, and 100 mM sodium chloride at a pH of 6.3. Both formulations were administered subcutaneously. The syringes were equipped with 27-gauge, -inch stake needles.
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Study Design
The institutional review board of MDS Pharma Services approved the protocol for this phase 1, single-center (MDS Pharma Services, Lincoln, Neb), open-label pharmacokinetic study. A balanced 2-treatment, 2-period, crossover design was used (Figure 1). This crossover design, which is commonly used to assess bioequivalence between drug formulations, allows each subject to act as his or her own control and decreases the variability for the comparison of the pharmacokinetic parameters of the 2 formulations (in comparison with a parallel design).
Subjects were randomly assigned in a 1:1 ratio to receive each treatment according to 1 of 2 treatment sequences: (1) a single injection of 50 mg/mL liquid etanercept, followed by 2 injections of 25 mg/mL reconstituted etanercept, or (2) 2 injections of 25 mg/mL reconstituted etanercept, followed by a single injection of 50 mg/mL liquid etanercept. Study treatments were separated by 28 days (washout period). All subcutaneous injections were administered in the right upper quadrant of the abdomen. The two 25-mg/mL injections were separated by no more than 1 minute; they were administered approximately 2 cm apart.
Subjects remained in the study facility for 72 hours after dosing and returned to the facility at predetermined time points throughout the study for collection of blood samples for laboratory, pharmacokinetic, and seroreactivity testing.
Pharmacokinetic End Points
The primary pharmacokinetic end point was the ratio of the geometric means of the area under the serum drug concentration-time curve from time zero to the time of the final quantifiable sample (AUC0-t) of a single 50-mg/mL subcutaneous injection of liquid etanercept compared with two 25-mg/mL subcutaneous injections of reconstituted etanercept after adjustment for the calculated amounts of protein delivered. Additional end points were the ratios of the unadjusted geometric means of AUC0-t and the adjusted and unadjusted geometric means of area under the serum drug concentration-time curve from time zero to infinity (AUC0-
) and Cmax.
Blood samples for pharmacokinetic analyses were obtained predose and at 6, 12, 24, 48, 60, 72, 96, 168, 264, and 336 hours after each dose of study drug. Serum etanercept concentrations were measured using a validated enzyme-linked immunosorbent assay (ELISA), with a lower limit of quantification of 0.625 ng/mL and interassay precision (ie, percentage coefficient variation) of 4% for quality controls.
Safety End Points
Safety was assessed throughout the study. Reports of treatment-emergent adverse events including injection site reactions; clinically significant changes in laboratory tests, vital signs, and electrocardiograms; and the incidence of antibody formation to etanercept were summarized. A physical examination, hematology and serum chemistry laboratory tests, and a urinalysis were done at screening, before each dose of study drug, 72 hours after each dose before discharge from the research facility (except urinalysis), and 14 days after administration of the second dose of the study drug. Clinical chemistry, hematology, and urinalysis data were evaluated for each subject, and values outside the normal reference ranges were identified. Abnormal laboratory values were not reported as adverse events, but any clinical consequences of the abnormalities were to have been reported as adverse events. Adverse events were coded using the Medical Dictionary for Regulatory Activities (MedDRA).
Serum samples were collected before each dose of etanercept (days 1 and 29) and at the follow-up evaluation (day 57) for testing for antibody to etanercept. A series of 3 validated ELISAs (screening, titration, and neutralizing antibody assays) was used to test for seroreactivity. A titration assay was done on samples that were positive for antibodies in the screening assay, and samples positive in the titration assay were to be further analyzed for the presence of neutralizing antibodies.
Statistical Methods
Previous studies in healthy volunteers showed a coefficient of variation for intrasubject error to be approximately 26% for AUC (data unpublished). Based on this estimate of variability, a sample size of 30 subjects would provide at least an 80% probability of achieving bioequivalence criteria for AUC (90% confidence interval for the ratio of geometric means for AUC0-t lying between 0.80 and 1.25), assuming there is no difference between the formulations. Thus, to allow for the possibility of all subjects not completing the study, a sample size of 36 subjects was chosen to ensure that at least 30 subjects would have pharmacokinetic profiles that could be evaluated.
Pharmacokinetic parameters were analyzed for subjects who completed both treatment periods. Pharmacokinetic parameters were derived using non-compartmental analysis from serum concentrations collected during the study. Parameters of AUC0-t, AUC0-, and Cmax were adjusted for the actual amount of drug substance delivered. The amount delivered was calculated for each subject from the protein concentrations of the liquid and reconstituted etanercept formulations that were reported on the certificates of analysis and from the volume administered (determined by weight). The unadjusted Cmax and time to maximum serum concentration (tmax) were observed values.
A linear/log trapezoidal rule was used to calculate AUC0-t. The area under the curve from the time of the last quantifiable concentration to infinity (AUCt-) was calculated by dividing the observed concentration at the time of the last quantifiable concentration by the terminal rate constant (
z). The AUC0- was calculated by the summation of AUC0-t and AUCt-. The apparent clearance (Cl/F) was calculated as the dose/AUC0-.
The adjusted and unadjusted pharmacokinetic parameters were analyzed using a crossover analysis of variance model. The Cmax and AUC were log-transformed before the analysis was conducted. The effects due to sequence, subject within sequence, treatment period, and treatment were included in the model. The 90% confidence intervals for the mean difference between the 2 treatments for the log-transformed AUC and Cmax were calculated using the residual error term from the analysis of variance model. Mean differences and confidence intervals were expressed as a percentage of the reconstituted lyophilized etanercept mean.
The liquid and reconstituted formulations were considered equivalent if the 90% confidence interval for the estimate of relative bioavailability, based on the adjusted AUC0-t, met the 0.80 to 1.25 criterion. The geometric means were presented for AUC0-t, AUC0-, and Cmax.
Descriptive statistics, including mean, standard deviation (SD), median, and range, were provided for all serum concentration data and pharmacokinetic parameters for each formulation.
All subjects who received at least 1 dose of study drug were included in the safety analyses. Treatment-emergent adverse events, clinical laboratory measurements, vital signs, and physical examinations were summarized for both etanercept formulations.
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The majority of subjects (86%) were white with a mean age of 30.8 years, and there were equal numbers of men and women. Baseline heights (mean, 172 cm), weights (mean, 74.6 kg), and body mass indices (mean, 25.0 kg/m2) were representative of a healthy population.
Pharmacokinetics
AUC0-t, AUC0-, and Cmax were adjusted for the actual amount of drug substance delivered based on protein concentrations and volume administered. The protein concentrations for the liquid and reconstituted formulations (obtained from the certificate of analysis assay results) were 49.2 and 24.5 mg/mL, respectively. The mean amount of etanercept delivered was 48.0 mg (range, 47.2-49.9 mg) for the liquid formulation and 48.0 mg (range, 46.6-54.3 mg) for the reconstituted formulation.
Mean AUC0-t, AUC0-, and Cmax values for the liquid formulation were 93.0%, 90.7%, and 98.5% of the respective parameters for reconstituted etanercept. These values of the ratios of geometric means and all of the associated confidence intervals were within the predefined equivalence interval of 80% to 125%. Mean (SD) pharmacokinetic data, point estimates, and 90% confidence intervals for the ratio (50 mg/mL liquid:2 x 25 mg/mL reconstituted) of geometric means after adjustment for volume and concentration are presented in Table II. The mean (SD) pharmacokinetic data, point estimates, and 90% confidence intervals before adjustment also satisfied the criterion for bioequivalence and are shown in Table III. The mean unadjusted etanercept concentration-time profiles for the 2 etanercept formulations are shown in Figure 2.
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Two subjects had parameters that met the predefined definitions of statistical outliers; that is, they had absolute value of the studentized residuals from the analysis of variance model greater than 3. When these 2 subjects were removed from the analyses, the criterion for bioequivalence was still met.
Safety
No major differences in the overall safety profiles were noted between the 2 etanercept formulations. Seventeen subjects (49%) reported adverse events after receiving the liquid formulation, and 14 (41%) reported adverse events after receiving the reconstituted formulation. All of the reported adverse events were mild to moderate in intensity, except for one case of a severe headache after the liquid etanercept injection. The headache, which lasted 24 hours, was not considered by the investigator to be related to study treatment. No subjects had serious adverse events or discontinued the study because of adverse events. Most of the events that were considered related to study treatment were injection site reactions, which occurred in 20% of the subjects after administration of liquid etanercept and in 21% after reconstituted etanercept. Adverse events that occurred in more than 2 subjects are presented in Table IV.
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The only notable laboratory abnormalities in this study (which were not reported as adverse events) were elevated alanine aminotransferase (54 U/L; normal range, 0-39 U/L), aspartate aminotransferase (112 U/L; normal range, 3-32 U/L), and lactate dehydrogenase (439 U/L; normal range, 109-214 U/L) on day 28 in a 37-year-old male subject. He received only the reconstituted etanercept formulation and was withdrawn from the study by the physician before administration of liquid etanercept. The subject's laboratory values returned to within normal limits by the day 49 follow-up visit, and he reported no adverse events during the study. The investigator reported this event as unrelated to study treatment.
Sera from 36 subjects was tested for antibodies to etanercept. Two subjects were found to be positive for antietanercept antibodies by the screening ELISA. Two other subjects were categorized as outliers on the assay and by protocol were routinely tested for neutralizing antietanercept antibodies. None of these 4 subjects were positive for neutralizing antietanercept antibodies.
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Based on findings in a previous bioequivalence study of the liquid and reconstituted etanercept formulations, meticulous attention was given to extracting the maximum amount of reconstituted etanercept from the vial and weighing of predose and postdose syringes, thus adjusting for the amount of protein delivered. In the previous study, differences in protein concentration and volume of drug delivered led to apparent differences in pharmacokinetic exposure. In this study, these factors were carefully evaluated at the outset and during the study and were pre-specified in the statistical analysis plan. The amount of drug delivered was determined from the protein concentrations of the liquid and reconstituted formulations (obtained from the certificates of analysis from lots used for the study), and the volume administered (calculated from the predose and postdose syringe weights and densities). Both with and without prospective adjustments for the estimated amount administered, the bioequivalence of the liquid formulation with the lyophilized formulation was demonstrated. The ratios of the geometric means and their 90% confidence intervals for adjusted AUC0-t, AUC0-, and Cmax were within the predefined 80% to 125% criterion for bioequivalence. We believe that this meticulous attention to properly extracting the reconstituted material from the vials was important in delivering comparable amounts of drug in this study. A slightly greater exposure to the lyophilized reconstituted etanercept in this repeat study in comparison with liquid was noted and is in contrast to the previous study in which lyophilized etanercept resulted in slightly less exposure compared with liquid. If the finding of slightly greater exposure for lyophilized product was to be valid, the potential explanations for this finding may relate to the number of injections (2 vs 1), volume administered (2 mL vs 1 mL), or concentration (25 mg/mL vs 50 mg/mL). Another potential reason for differences relates to posttranslational changes, such as degree of sialylation, according to a given lot. In the clinic, however, it is likely that 50 mg/mL liquid etanercept results in slightly higher exposure for patients because the same care in extracting as much material as possible may not be consistently applied.
Thus, this study demonstrated that a single subcutaneous injection of 50 mg/mL liquid etanercept is bioequivalent to 2 subcutaneous injections of 25 mg/mL reconstituted etanercept and that the liquid etanercept formulation is safe and well tolerated. This 50-mg/mL liquid etanercept formulation is likely to be more convenient for patients who require 50 mg etanercept weekly. The 2 formulations are expected to deliver comparable clinical outcomes, based on the pharmacokinetic findings of this study.
This protocol was reviewed and approved by the MDS Pharma Services Institutional Review Board, Lincoln, Nebraska. This study was supported by Immunex Corporation, a wholly owned subsidiary of Amgen Inc, Thousand Oaks, California. Results of this study were presented in a poster at the American College of Rheumatology Annual Meeting, October 2004. The authors thank Alan Marion, MD, PhD, of MDS Pharma Services, Lincoln, Nebraska, and Binodh DeSilva and Bassam Abosaleem of Amgen Inc, Thousand Oaks, California, for their contributions to this investigation, and Orysia V. Lutz for assistance with writing the manuscript.
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REFERENCES |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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1. Korth-Bradley JM, Rubin AS, Hanna RK, Simcoe DK, Lebsack ME. The pharmacokinetics of etanercept in healthy volunteers. Ann Pharmacother. 2000;34: 161-164.[Abstract]
2. Lee H, Kimko HC, Rogge M, Wang D, Nestorov I, Peck CC. Population pharmacokinetic and pharmacodynamic modeling of etanercept using logistic regression analysis. Clin Pharmacol Ther. 2003;73: 348-365.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
3. Zhou H, Buckwalter M, Boni J, et al. Population-based pharmacokinetics of the soluble TNFr etanercept: a clinical study in 43 patients with ankylosing spondylitis compared with post hoc data from patients with rheumatoid arthritis. Int J Clin Pharm Ther. 2004;42: 267-276.[Web of Science][Medline] [Order article via Infotrieve]
4. Etanercept [prescribing information]. Thousand Oaks, Calif: Immunex Corp; 2006. Available at: http://www.enbrel.com/prescribing-information.jsp. Accessed January 24, 2006.
5. Keystone EC, Schiff MH, Kremer JM, et al. Once-weekly administration of 50 mg etanercept in patients with active rheumatoid arthritis. Arthritis Rheum. 2004;50: 353-363.[CrossRef][Web of Science][Medline]
[Order article via Infotrieve]
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