Subjects
Healthy male and female subjects 18–55 years of age were eligible for enrollment. Subjects were required to have a body mass index ≥ 18.5 to ≤ 29.9 kg/m2 and were excluded for any clinically significant medical condition. Subjects who were not surgically sterile, or female subjects who were not postmenopausal for ≥ 1 year and of childbearing potential, were required to follow protocol-specified contraceptive methods. Subjects were required to refrain from the use of any drug with potential for drug–drug interactions affecting the pharmacokinetics, including prescription and non-prescription medications, or herbal remedies, within 14 days prior to the first dose of the study drug.
Study Design
This was a single-dose, open-label, randomized, two-way crossover study evaluating the pharmacokinetics of MMF after a single dose of the test product vs the reference product under fasting conditions over two dose periods separated by 2 days. Healthy subjects were randomized to one of two treatment sequences prior to the first dose to minimize the period effect in a crossover study. In each period, subjects received one of the two treatments based on the treatment sequence: (1) test: a single oral dose of MMF 190 mg administered as two Bafiertam™ 95 mg delayed-release (DR) capsules, and (2) reference: DMF 240 mg administered as one Tecfidera® 240 mg DR capsule. Each dose of study drug was administered with 240 mL of water after an overnight fast, which continued for another 4 h post-dose. Blood samples for measurement of plasma MMF concentrations were collected in each period within 15 min prior to dosing, and at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 9, 10, 11, 12, and 24 h post-dose. Blood samples were collected into prechilled Vacutainer® tubes containing sodium fluoride and potassium oxalate as the stabilizer and anticoagulant, respectively. The stabilizer (sodium fluoride) was used to quench the hydrolysis of DMF, if any, to MMF immediately upon blood collection. Prior to the clinical study, the selected anticoagulant and stabilizer were verified by validation experiments conducted by BioPharma Services to be sufficient to stop the esterase hydrolysis. Immediately upon blood collection, the collection tubes were gently inverted to allow mixing of the blood, anticoagulant, and the stabilizer, and were then cooled in an ice bath and centrifuged (approximately at 2056 × gravity for 7 min) under refrigeration (approximately 4 °C) as soon as possible and no later than 60 min after blood collection. Plasma samples were stored at approximately − 70 °C or lower until analysis.
This study was conducted in accordance with the US Food and Drug Administration (FDA) guidance for bioavailability and bioequivalence studies for orally administered drug products [9]. The study received institutional review board approval and all subjects provided written informed consent prior to the conduct of study-related procedures. The study was conducted at Celerion’s phase I clinical research unit (Tempe, AZ, USA) in compliance with the protocol, Good Clinical Practice guidelines, the ethical principles of the Declaration of Helsinki, and all applicable regulatory requirements.
PK Endpoints and Analysis
The primary endpoints for bioequivalence assessment are AUC0–inf and C
max of MMF between the two treatments (MMF 190 mg vs DMF 240 mg). The AUC0–t was also compared between treatments as supportive information. The definitions of these PK parameters are as follows: C
max is the maximum observed plasma concentration, AUC0–t is the area under the plasma concentration–time curve (AUC) from time zero (dosing time) to the last time point, t, with measurable analyte concentration, and AUC0–inf is AUC0–t plus the extrapolated AUC from time t to infinity. Additional PK parameters including the percent of AUC0–inf that is extrapolated (AUC%extrap), time to reach C
max (tmax), and the apparent half-life of the drug in plasma (t
1/2) of MMF were computed for each treatment but not compared between treatments. Pharmacokinetic parameters of MMF were determined by a noncompartmental analysis of individual plasma concentration–time data using Phoenix® WinNonlin® Version 6.3 or higher (Certara, Princeton, NJ, USA).
Sample Size
A sample size of 44 subjects was calculated according to Hauschke et al. [10] using a power of at least 95% and an alpha error of 5%. The power was defined as the probability of having a 90% CI for the geometric least-squares mean (GLSM) ratio, test/reference, for each primary PK parameter to fall within the acceptance criteria of 80.00–125.00%. A true GLSM ratio between 95 and 105% was assumed and an intra-subject coefficient of variation (CV) of 24% was used for estimating the sample size. To ensure having 44 subjects in the study with evaluable PK data (e.g., exposure to treatment, availability and validity of measurements, and absence of major protocol violations), six additional subjects were enrolled with a total of 50 subjects dosed to account for potential dropouts. Statistical analysis was performed on all subjects contributing PK parameters of MMF (Cmax, AUC0–inf, and AUC0–t). However, statistical analysis for bioequivalence assessment was based on PK parameter data from subjects who completed the study and had sufficient data for a pairwise comparison (i.e., from both treatments).
Plasma Concentrations of MMF
The analysis of plasma MMF concentrations was conducted using a validated method to determine MMF in human plasma containing NaF/K-oxalate/1.0% phosphoric acid using high-performance liquid chromatography with tandem mass spectrometry. The method was developed and validated by BioPharma Services (Toronto, ON, Canada). Sample treatment involves protein precipitation and filtration from 100 μL of human plasma; MMF-d5 was used as the internal standard. The compounds were identified and quantified by liquid chromatography with tandem mass spectrometry over a theoretical concentration range of 25–2500 ng/mL, with a lower limit of quantitation of 25 ng/mL. This method met acceptance criteria with respect to specificity, sensitivity, precision, accuracy, matrix effect, linearity, percent extraction yields, and dilution integrity according to the FDA/CVM Guidance 145: Bioanalytical Method Validation (September 2013 and May 2001). Stability evaluations in matrix and solutions also met acceptance criteria, demonstrating no significant degradation of MMF and MMF-d5 (internal standard) over the storage durations for the clinical samples and conditions examined during the method validation. This method was fully validated in conformance with current FDA Regulations (21 CFR Part 58), the FDA/CVM Guidance 145: Bioanalytical Method Validation (September 2013 and May 2001), and the principles, as they apply to bioanalysis, of the OECD Series on Principles of Good Laboratory Practice (1997).
Safety and Tolerability
Safety and tolerability were assessed by analysis of treatment-emergent adverse events (TEAEs) reported from the time of the first dose through follow-up (telephone or e-mail contact approximately 7 days after the last dose of the study drug). Treatment-emergent adverse events were coded using the Medical Dictionary for Regulatory Activities (MedDRA®) Version 19.1. All TEAEs were graded as mild (event was easily tolerated and did not interfere with daily activity), moderate (event interfered with daily activity, but the subject was still able to function; medical intervention may have been considered), or severe (event was incapacitating and required medical intervention). Laboratory parameters (hematology, chemistry, and urinalysis) and vital signs were collected through day 2 of period 2. No inferential statistics were performed for safety assessments.
Statistical Analyses
Summary statistics (arithmetic mean; standard deviation; %CV, geometric %CV, standard error of the mean; median, minimum, maximum) were determined for continuous variables and number and percent for categorical variables and were summarized by treatment. Statistical analysis of PK parameters was performed on natural log (ln)-transformed AUC0–t, AUC0–inf, and Cmax using analysis of variance (ANOVA). The ANOVA model included sequence, treatment, and period as fixed effects, and subject nested within a sequence as a random effect. The ANOVA included calculation of least-squares means of the ln-transformed parameter as well as the least-squares mean difference between treatments.
Ratios of GLSM, test vs reference, were calculated by exponentiating the least-squares mean difference between treatments from the ANOVA on the ln-transformed data. The 90% CIs for the GLSM ratios were derived similarly as the GLSM. Bioequivalence criteria are met if the 90% CIs for the ratios of GLSMs of both C
max and AUC0–inf of the test (Bafiertam™, MMF) to the reference (Tecfidera®, DMF) fall within the boundaries of 80.0% and 125%. Statistical analysis was performed using SAS Version 9.3 or higher (SAS Institute Inc., Cary, NC, USA).