Proton Pump Inhibitors Do Not Affect the Bioavailability of a Novel Liquid Formulation of Levothyroxine.

OBJECTIVE: This study evaluates the impact of a representative proton pump inhibitor (PPI) (omeprazole), administered simultaneously or staggered, on the pharmacokinetics of levothyroxine (LT4) solution (Tirosint-SOL). METHODS: This was a randomized, 3-way crossover, comparative bioavailability study in 36 healthy adults under fasting conditions. Omeprazole 40 mg delayed-release capsule was administered once daily from Day 1 to 6 (mornings, Treatment-A; evenings, Treatment-B; none, Treatment-C) to increase and stabilize gastric pH. In the morning of Day 5, a single dose of LT4 solution 600 mcg was administered. Blood samples were collected 0 to 48 hours post-LT4 administration. Noncompartmental pharmacokinetic parameters were calculated for total serum thyroxine using baseline-corrected data. Maximum concentration (Cmax) and area under the concentration-time curve (AUC0-48) were included in an analysis of variance to obtain geometric mean ratios and 90% confidence intervals. RESULTS: For both comparisons (A/C and B/C), geometric mean ratios and 90% confidence intervals for all parameters were within the equivalence boundaries (80%-125%), indicating bioequivalence: for A/C, AUC0-48 98.98% [94%-104%], and Cmax 91.68% [87%-97%]; for B/C, AUC0-48 98.94% [95%-103%], and Cmax 94.90% [90%-100%]. Median Tmax (time associated with Cmax) was similar across treatments. CONCLUSION: This study demonstrated that Tirosint-SOL bioavailability is unaffected by coadministration of a representative PPI, given simultaneously or staggered by about 12 hours, compared to administration of LT4 solution alone. For hypothyroid patients on PPI therapy, administration of LT4 solution may reduce variations in thyroid stimulating hormone levels related to intermittent use of acid-reducing drugs and consequently the need for dose adjustments.

Use of the Same Model or Modeling Strategy Across Multiple Submissions: Focus on Complex Drug Products.

Evidence shows that there is an increasing use of modeling and simulation to support product development and approval for complex generic drug products in the USA, which includes the use of mechanistic modeling and model-integrated evidence (MIE). The potential for model reuse was the subject of a workshop session summarized in this review, where the session included presentations and a panel discussion from members of the U.S. Food and Drug Administration (FDA), academia, and the generic drug product industry. Concepts such as platform performance assessment and MIE standardization were introduced to provide potential frameworks for model reuse related to mechanistic models and MIE, respectively. The capability of models to capture formulation and product differences was explored, and challenges with model validation were addressed for drug product classes including topical, orally inhaled, ophthalmic, and long-acting injectable drug products. An emphasis was placed on the need for communication between FDA and the generic drug industry to continue to foster maturation of modeling and simulation that may support complex generic drug product development and approval, via meetings and published guidance from FDA. The workshop session provided a snapshot of the current state of modeling and simulation for complex generic drug products and offered opportunities to explore the use of such models across multiple drug products.

Establishing the suitability of model-integrated evidence to demonstrate bioequivalence for long-acting injectable and implantable drug products: Summary of workshop.

On November 30, 2021, the US Food and Drug administration (FDA) and the Center for Research on Complex Generics (CRCG) hosted a virtual public workshop titled "Establishing the Suitability of Model-Integrated Evidence (MIE) to Demonstrate Bioequivalence for Long-Acting Injectable and Implantable (LAI) Drug Products." This workshop brought relevant parties from the industry, academia, and the FDA in the field of modeling and simulation to explore, identify, and recommend best practices on utilizing MIE for bioequivalence (BE) assessment of LAI products. This report summerized presentations and panel discussions for topics including challenges and opportunities in development and assessment of generic LAI products, current status of utilizing MIE, recent research progress of utilizing MIE in generic LAI products, alternative designs for BE studies of LAI products, and model validation/verification strategies associated with different types of MIE approaches.

A Novel Levothyroxine Solution Results in Similar Bioavailability Whether Taken 30 or Just 15 Minutes Before a High-Fat High-Calorie Meal.

Background: Levothyroxine (LT4) sodium is a standard treatment for hypothyroidism. Its absorption and bioavailability when taken as a tablet have been shown to be significantly decreased with concomitant food ingestion. Therefore, LT4 formulations are recommended to be taken on an empty stomach, at least 30, ideally 60, minutes before breakfast, potentially affecting adherence to therapy. A novel LT4 solution (Tirosint®-SOL) has been shown to result in a faster absorption process than tablets or soft-gel capsule formulations. The objective of this trial was to evaluate the bioavailability of this preparation taken 15 minutes before a high-fat high-calorie meal in comparison with the minimally recommended 30-minute interval. Methods: Thirty-six (33 completers, 24 males and 9 females) healthy volunteers participating in the randomized study took 600 mcg of LT4 oral solution, single doses after a 10-hour fast, 15 or 30 minutes before a high-fat, high-calorie, FDA-approved standardized meal in a controlled research setting. We measured serum total thyroxine using Liquid Chromatography with Tandem Mass Spectrometry at baseline and multiple time points up to 72 hours after LT4 administration. The predefined equivalence boundaries for the extent of exposure reflected by the area under the curve (AUC) were 80-125%. The washout period was at least 35 days. Results: The geometric mean ratios and confidence intervals (CIs) for the baseline-adjusted extent of exposure represented by AUCs truncated at both 48 and 72 hours after dosing (AUC0-48: 90% [90% CI 86-94]; and AUC0-72: 92% [90% CI 87-97]) were within the prespecified equivalence boundaries. The baseline-adjusted peak concentration was also clinically similar (Cmax: 85% [90% CI 80-90]). The median tmax was 1.5 hours in each group. The rate of adverse events was similar between groups. Conclusions: We observed no significant difference in the pharmacokinetic properties of a novel LT4 solution administered 15 and 30 minutes before a high-fat high-calorie meal in normal subjects. Further research is needed to evaluate (a) the differences in overall bioavailability at other time points (including immediately premeal) and (b) the real-world effectiveness of this preparation in newly proposed administration conditions to optimize treatment outcomes in hypothyroid patients.

Influence of Different Populations on Pharmacokinetic Bioequivalence Results: Can We Extrapolate Bioequivalence Results from One Population to Another?

Purpose: Over the last 15 years, an ever-increasing proportion of pharmacokinetic bioequivalence studies for European/North American generic submissions appeared to have been conducted in geographical/ethnic populations other than those for which the drug is marketed for. The results of pharmacokinetic bioequivalence studies have traditionally been considered to be insensitive to the population studied. However, several recent studies have suggested that this may not necessarily be true. The objective of this study was to investigate whether there were any concerns regarding the current practice of extrapolating bioequivalence study results from one geographic/ethnic population to another. METHODS: In order for a regulatory agency to use bioequivalence results from one population to another, two formulations assessed as bioequivalent under fasted and fed conditions in one population must be bioequivalent in a geographically/ethnically different population under both conditions. Unfortunately, bioequivalence studies between a generic and its reference product for one submission are conducted using only one geographical/ethnic population. As bioequivalence study results between two populations for the same generic and reference products are not available, the food effect for the same reference product between two populations was compared. This is based on the rationale that if two products are bioequivalent under both fasted and fed conditions in two populations, even if there are PK differences in the product exposures between these two populations, the test to reference ratio, as well as the food effect, will remain constant within each population. Food effect (fed/fasted ratio) was calculated using pharmacokinetic data from publicly available regulatory resources and compared between two geographical/ethnic populations using the same reference for each studied drug product. Meta-analyses were conducted. RESULTS: Statistically significant differences (P<0.05) were found in the food effect between two populations for nine out of the ten (90%) available studied products. Among these, an observed clinical difference was suggested in three out of nine (33%) products. CONCLUSION: These results suggest that bioequivalence results from one population may not always be representative of what may be found in another population.

A randomized, double-blind, placebo-controlled, single and multiple ascending dose Phase 1 study to determine the safety, pharmacokinetics and food and faecal microbiome effects of ibezapolstat administered orally to healthy subjects.

BACKGROUND: Clostridioides difficile infection is the most common cause of healthcare-associated infections in the USA, with limited treatment options. Ibezapolstat is a novel DNA polymerase IIIC inhibitor with in vitro activity against C. difficile. OBJECTIVES AND METHODS: Randomized, double-blind, placebo-controlled study to assess the safety, tolerability and pharmacokinetics of ibezapolstat in healthy volunteers. Microbiome changes associated with ibezapolstat were compared with vancomycin over a 10 day course using shotgun metagenomics. RESULTS: A total of 62 subjects aged 31 ± 7 years (45% female; average BMI: 25 ± 3 kg/m2) were randomized. Ibezapolstat was well tolerated with a safety signal similar to placebo. Ibezapolstat had minimal systemic absorption with the majority of plasma concentrations less than 1 µg/mL. In the multiday, ascending dose study, ibezapolstat concentrations of 2000 µg/g of stool were observed by Day 2 and for the remainder of the dosing time period. In the multiday, multiple-dose arm, baseline microbiota was comparable between subjects that received ibezapolstat compared with vancomycin. At Day 10 of dosing, differential abundance analysis and ß-diversity demonstrated a distinct difference between the microbiome in subjects given vancomycin compared with either dose of ibezapolstat (P = 0.006). α-Diversity changes were characterized as an increase in the Actinobacteria phylum in subjects that received ibezapolstat and an increase in Proteobacteria in subjects given vancomycin. CONCLUSIONS: Ibezapolstat was shown to be safe and well tolerated, with minimal systemic exposure, high stool concentrations and a distinct microbiome profile compared with oral vancomycin. These results support further clinical development of ibezapolstat for patients with C. difficile infection.

Novel Approach for the Bioequivalence Assessment of Topical Cream Formulations: Model-Based Analysis of Tape Stripping Data Correctly Concludes BE and BIE.

PURPOSE: The purpose of this study was (a) to suggest a novel dermatopharmacokinetic (DPK) approach from which pharmacokinetic parameters relevant to the bioequivalence (BE) assessment of a topical formulation can be deduced while circumventing the need for numerous measurements and assumptions, and (b) to investigate whether this approach enables the correct conclusion of BE and bioinequivalence (BIE). METHODS: Bioequivalent and bioinequivalent formulations of acyclovir were compared versus a reference product (Zovirax®). Tape Stripping was conducted at only one dose duration during the uptake phase to generate drug content in stratum corneum versus time profiles, each time point corresponding to one stripped layer. Nonlinear mixed effect modeling (ADAPT5®) (MLEM algorithm) was used to fit the DPK data and to estimate the rate (Kin) and extent (FS) of drug absorption/input into the skin. Results were evaluated using the average BE approach. RESULTS: Estimated exposure metrics were within the usual BE limits for the bioequivalent formulation (FS: 102.4 [90%CI: 97.5-107.7]; Kin: 94.2 [90%CI: 83.7-106.0]), but outside those limits for the bioinequivalent formulation (FS: 43.4 [90%CI: 27.9-67.6]; Kin: 54.5 [90%CI: 36.6-81.1]). CONCLUSIONS: The proposed novel DPK approach was shown to be successful, robust and applicable to assess BE and BIE correctly between topical formulations.

Summary report of second EUFEPS/AAPS conference on global harmonization in bioequivalence.

The Global Bioequivalence Harmonization Initiative (GBHI) was launched by the Network on Bioavailability and Biopharmaceutics (BABP) under the auspices of European Federation for Pharmaceutical Sciences (EUFEPS) several years ago. Since 2015, EUFEPS in collaboration with the American Association of Pharmaceutical Scientists (AAPS) has organized three international conferences to support global harmonization of regulatory requirements for bioequivalence (BE) assessment. These conferences provided an open forum for pharmaceutical scientists from academia, industry and regulatory agencies to discuss various BE topics at issue. The current report summarizes the discussion of BE issues at the 2nd GBHI conference held in 2016, Rockville, USA. Three important BE topics were discussed at the meeting: (a) prodrugs and compounds with pre-systemic extraction, (b) scaling procedures and two-stage designs, and (c) exclusion of pharmacokinetic data in BE assessment. The presentations and discussions of these issues have enhanced the mutual understanding of scientific background for BE evaluation and further facilitated harmonization of regulatory approaches for establishing BE of multisource drug products.

Opportunities and Challenges Related to the Implementation of Model-Based Bioequivalence Criteria.

The science of bioequivalence and biosimilarity has greatly evolved over the past 3 decades. Current methods for assessing bioequivalence mostly rely on noncompartmental pharmacokinetic (PK) analyses, which have proven to be reliable and robust for most products. However, the development of more complex products is forcing scientists and regulators to consider alternative approaches, including those derived from model-based population PK analyses. This article will examine the strengths and weaknesses of standard noncompartmental methods and compare them to model-based approaches, including a comparison of metrics associated with each method. Specific situations for which model-based approaches could prove to be more suitable will be presented, as well as potential bioequivalence metrics that could be considered for bioequivalence comparisons. The opportunities and challenges that are associated with these novel methods will also be discussed.

Revisiting FDA's 1995 Guidance on Bioequivalence Establishment of Topical Dermatologic Corticosteroids: New Research Based Recommendations.

PURPOSE: As per the US FDA guidance issued on June 2, 1995, the establishment of bioequivalence for topical dermatologic corticosteroids is based on comparing the pharmacodynamic (PD) effects of Test and Reference products at the dose duration corresponding to the population ED50, determined either by naïve pooled data or nonlinear mixed effect modeling (NLME). The guidance was introduced using a study case example where the expectation maximization (EM) NLME algorithm, as implemented in P-PHARM®, was used. Although EM methods are relatively common, other methods such as the First-Order Conditional Estimation (FOCE) as implemented in the NONMEM® software are even more common. The objective of this study was to investigate the impact of using different parametric population modeling/analysis methods and distribution assumptions on population analysis results. METHODS: The dose duration-response data from 11 distinct skin blanching blinded pilot studies were fitted using FOCE (NONMEM®) and an EM algorithm (ADAPT5® (MLEM)). Three different Emax models were tested for each method. Population PD estimates and associated CV%, and the agreement between model predicted values and observed data were compared between the two methods. The impact of assuming different distributions of PD parameters was also investigated. RESULTS: The simple Emax model, as proposed in the FDA guidance, appeared to best characterize the data compared to more complex alternatives. The MLEM method in general appeared to provide better results than FOCE; lower population PD estimates with less inter-individual variability, and no variance shrinkage issues. The results also favored ln-normal versus normal distribution assumptions. CONCLUSIONS: The population ED50 estimates were influenced by both the type of population modeling methods and the distribution assumptions. We recommend updating the FDA guidance with more specific instructions related to the population approach to be used (EM-like versus FOCE-like methods) and to the normality assumptions that need to be set (ln-normal versus normal distribution).

Identification of Mechanism and Pathway of the Interaction between the African Traditional Medicine, Sutherlandia Frutescens, and the Antiretroviral Protease Inhibitor, Atazanavir, in Human Subjects Using Population Pharmacokinetic (PK) Analysis.

Although the use of the indigenous Southern African plant, Sutherlandia frutescens (SF) for the treatment of HIV/AIDS has previously been described, the risk which it may pose to the safety and efficacy of ARVs and the potential mechanisms which underlie such effects may have clinical significance and relevance. The protease inhibitor (PI), atazanavir (ATV) is a substrate of the efflux transporter, P-gp which modulates absorption in the small intestine, as well as CYP3A4 and CYP3A5enzymes which facilitate metabolism in the small intestine and liver. The objective of this study was to investigate the effect of SF on the pharmacokinetics (PK) of atazanavir (ATV) and to use a population PK analysis to fit and explain plasma concentration vs. time profiles of ATV generated in a previously conducted study in healthy male subjects in order to understand and postulate on the potential mechanism(s) of the drug-drug interaction. The population PK Compartmental Analysis of ATV before and after a two-week regimen of Phyto Nova Sutherlandia SU1 tablets which contain SF plant material indicated that a two compartment model with a dual absorption mechanism best explained the data. The dual absorption mechanism is hypothesized to reflect "passive" (first-order, Ka parameter) and "active" (zero-order, K0 parameter) absorption processes. The model suggested that the mechanism by which SF reduced the overall bioavailability of ATV may be modulated via the inhibition of the "active" absorption process. This study has highlighted the utility of population PK analyses in postulating probable mechanism(s) whereby an ATM or a herbal medicine interacts with an allopathic drug.

Model-Informed Drug Development and Review for Generic Products: Summary of FDA Public Workshop.

On October 2nd and 3rd , 2017, the US Food and Drug Administration (FDA) hosted a public workshop titled "Leveraging Quantitative Methods and Modeling to Modernize Generic Drug Development and Review."1 This report summarizes Session 2 of the public workshop: "Model Informed Drug Development and Review for Generic Products." The session focused on the application of quantitative methods and modeling in modernizing the generic drug development and review.

Effect of Food on the Pharmacokinetics of Single- and Multiple-Dose Hydrocodone Extended Release in Healthy Subjects.

BACKGROUND AND OBJECTIVES: Food intake can alter the pharmacokinetics of certain medications, including changes in their oral bioavailability, which is of particular concern for extended-release (ER) opioids because of the high drug loads. Two randomized, open-label studies assessed the effect of food on the pharmacokinetics of single and multiple doses of hydrocodone ER formulated with CIMA® Abuse-Deterrence Technology. METHODS: Healthy subjects in fed and fasted states received single 90-mg doses of hydrocodone ER (Studies 1 and 2) or multiple doses of hydrocodone ER (45 mg twice daily on days 2-3, 60 mg twice daily on days 4-5, 90 mg twice daily on days 6-10, and 90 mg once in the morning on day 11) (Study 2). Naltrexone was administered to minimize opioid-related adverse events. Pharmacokinetic parameters included maximum hydrocodone plasma concentration (C max) and area under the concentration-versus-time curve from time 0 to infinity (AUC0-∞) in Study 1 (day 1) and for one dosing interval at steady state (AUCτ,ss) in Study 2 (day 11). Before conducting the multiple-dose study, single-dose data were fitted with a population pharmacokinetic methodology. RESULTS: In total, 40 subjects were randomized to Study 1 and 43 subjects were randomized to Study 2. While overall exposure (AUC0-∞) was relatively similar (least squares mean ratio [90% CI]: 1.11 [1.06-1.16]), results indicated that the single-dose C max was 40% higher under fed versus fasted conditions (least squares mean ratio [90% CI]: 1.40 [1.31-1.51]; Study 1). Modeling of single-dose data predicted that the effect of food would be much less at steady state [predicted fed:fasted C max at steady state (C max,ss) and AUCτ,ss ratios of 1.18 and 1.09, respectively]. The multiple-dose study results validated these predicted ratios and indicated that the steady-state 90% CIs were within 0.80-1.25 for the fed:fasted C max,ss (1.14 [1.07-1.21]) and AUCτ,ss (1.11 [1.04-1.17]) parameters, indicating that clinically meaningful food effects at steady state are not expected. CONCLUSION: No evidence of an effect of food was found on the pharmacokinetics of hydrocodone ER after multiple days of twice-daily dosing.

Levothyroxine soft capsules demonstrate bioequivalent pharmacokinetic exposure with the European reference tablets in healthy volunteers under fasting conditions.

OBJECTIVE: To assess the bioequivalence (BE) potential under fasting conditions between levothyroxine soft capsules and the European reference tablet formulation. METHODS: Two studies were conducted to assess the BE potential as per European regulations. Study 1 was a two-way crossover BE study comparing a high strength of levothyroxine soft capsules versus levothyroxine tablets (200 µg), while study 2 was a three-way crossover dosage form proportionality study between low, medium, and high strengths of soft capsules. 70 healthy adult subjects participated in the two studies. Each treatment consisted of a 600-µg dose of levothyroxine sodium, administered under fasting conditions. Blood samples were collected for levothyroxine (T4) assay prior to dosing and up to 72 hours post dose. A washout of 35 days separated treatments in each study. Pharmacokinetics was assessed using noncompartmental methods. RESULTS: A total of 61 subjects completed the studies. Baseline-adjusted total T4 ratios (test/reference) and 90% confidence intervals (CIs) between soft capsules and tablets were within 80.00 - 125.00%. Comparison of the three strengths of soft capsules indicated pharmacokinetic equivalence between them (ratios and 90% CIs were contained within 80.00 - 125.00%). Overall, levothyroxine sodium was well tolerated with all products when given as single oral doses of 600 µg, except for 1 serious adverse event of secondary bacteremia reported in study 2, deemed not to be related to treatment. CONCLUSION: Levothyroxine soft capsules meet BE criteria in terms of systemic exposure when compared to a European reference tablet under fasting conditions in healthy volunteers.

When Bioequivalence in Healthy Volunteers May not Translate to Bioequivalence in Patients: Differential Effects of Increased Gastric pH on the Pharmacokinetics of Levothyroxine Capsules and Tablets.

PURPOSE: Clinical studies have suggested that proton pump inhibitors may decrease levothyroxine absorption and an in vitro study suggested that the effect of pH on dissolution may differ with formulation. To determine the impact of formulation on the pharmacokinetics of levothyroxine in altered gastric pH conditions, this study compared the pharmacokinetics of levothyroxine capsules and tablets, two formulations deemed bioequivalent in healthy volunteers under fasting conditions, when taken with or without esomeprazole. METHODS: Two clinical studies were conducted in healthy volunteers given single dose levothyroxine (600 mg) with a 45-day washout period. In Study 1 (parallel-design/two-way crossover), 16 subjects received either levothyroxine capsules or tablets, each group with or without prior administration of intravenous esomeprazole (maximum dose of 80 mg). In Study 2 (two-way crossover), 16 subjects received both capsules or tablets after intravenous esomeprazole. Blood samples were collected pre-dose and up to 24 hours post-dose. Baseline-adjusted pharmacokinetic parameters were calculated: Cmax (maximal concentration), Tmax (time to Cmax), AUC0-t (area under the concentration-time curve from 0 to the last detectable concentration), AUC0-6 and AUC0-12 (areas under the curve from 0 to 6 and 12 hours, respectively). Analyses of variance were conducted to compare ln-transformed Cmax and AUC. Non-parametric Tmax analyses were done. RESULTS: In Study 1, esomeprazole caused a greater decrease in overall levothyroxine exposure of tablets vs. capsules (13% vs 6% for Cmax, 18% vs. 14% for AUC(0-6), 17% vs. 5% for AUC(0-12) and 10% vs. 8% for AUC(0-t)). In Study 2 esomeprazole administration resulted in a 16% smaller levothyroxine exposure with tablets vs. capsules. No statistically significant differences in Tmax were found. CONCLUSIONS: Although both formulations are considered "bioequivalent" in healthy volunteers, they may not necessarily be bioequivalent in patients with impaired gastric pH conditions. Levothyroxine capsules may therefore be more appropriate for patients with decreased gastric acidity.

Novel population pharmacokinetic method compared to the standard noncompartmental approach to assess bioequivalence of iron gluconate formulations.

PURPOSE: Iron-containing products are atypical in terms of their pharmacokinetic properties because iron is only removed by plasma sampling and is non-linear. This study aims to present a novel way of assessing the relative bioavailability of two sodium ferric gluconate complex (SFGC) formulations and compare this approach to a standard previously published noncompartmental approach. METHODS: Data were from open-label, randomized, single-dose studies (Study 1 was parallel whereas Study 2 was crossover). Subjects with low but normal iron levels were infused IV SFGC in sucrose by GeneraMedix Inc. and/or Ferrlecit ® Injection (Watson Laboratories Inc.). In Study 1 (n=240), 125 mg was infused over 10 minutes. In Study 2 (n=29), 62.5 mg was infused over 30 minutes. Samples were assayed for total iron (TI) and transferrin-bound iron (TBI) over 36 hours (Study 1) or 72 hours (Study 2) post-dose. Studies 1 and 2 used standard noncompartmental analysis. Study 2 also used population PK (PPK) analyses with ADAPT 5®. The final model predicted SFGC area-under-the-curve (AUCpred) and maximal concentration (Cmaxpred). Analyses of variance was conducted on ln-transformed PK parameters. Ratios of means and 90% confidence intervals (CIs) were estimated. Bioequivalence was demonstrated if values were within 80-125%. RESULTS: For Study 1, ratios and 90% CIs for TI baseline-corrected Cmax and AUC0-36 were 100.4 (96.5 - 104.5) and 99.7 (94.2 - 105.5). For TBI, results for TI baseline-corrected Cmax and AUC0-36 were 86.8 (82.7 - 91.1) and 92.4 (85.6 - 99.7). For Study 2, a multi-compartmental model simultaneously described the PK of TI, TBI and SFGC. Ratios and 90% CIs for SFGC Cmaxpred and AUCpred were 89.9 (85.9 - 94.0) and 89.7 (85.7 - 93.9), while ratios and 90% CI obtained from the noncompartmental analysis of Study 2 did not meet BE criteria because of low power. CONCLUSIONS: Both the standard and PPK modeling approach suggested bioequivalence between the iron products. However, with the PPK method, less subjects were required to meet study objectives compared to the standard noncompartmental approach which required considerably more subjects (29 vs 240).

Bioequivalence of oxycodone hydrochoride extended release tablets to marketed reference products OxyContin® in Canada and US.

INTRODUCTION: Oxycodone is a semisynthetic opioid agonist used for the relief of moderate to severe pain. A new generic oxycodone hydrochloride (HCl) extended release (ER) tablet is currently being developed by Ranbaxy Pharmaceutical Inc., New Brunswick, NJ, USA. OBJECTIVE: To assess relative bioavailability of a new generic (test) formulation of oxycodone hydrochloride (HCl) extended release (ER) tablets with that of marketed reference products, OxyContin®, in Canada and USA, in healthy adult subjects under fasting and fed conditions. METHODS: Five studies were conducted in all, three of which were designed to comply with the regulatory criteria for marketing a new generic formulation of OxyContin® in Canada and the remaining two to comply with regulatory criteria for marketing a new generic formulation of OxyContin® in the USA. Each study was a balanced, randomized two-period, two-treatment, two-sequence, crossover design. A single oral dose of test or reference product was given in Period 1, followed by a 7-day washout period, after which subjects received the alternative product in Period 2. In order to block the pharmacological effects of oxycodone, subjects were administered naltrexone HCl (1 × 50 mg tablet) 12 hours prior to oxycodone HCl administration, concurrent with oxycodone HCl administration, and 12 hours after oxycodone HCl administration. Throughout the confinement portion of the study, adverse events were closely monitored. Serial blood samples were collected, following which oxycodone in plasma was estimated using a validated analytical procedure. RESULTS: Oxycodone was well tolerated by subjects in both periods of each study under both fed and fasted conditions. No serious adverse events were observed. The ratios of geometric means for AUC0-t and Cmax and the affiliated 90% confidence intervals for AUC were within acceptance range recommended by Health Canada. These criteria were met for both the raw data as well as data corrected for measured drug content (potency). The ratios of geometric means and the 90% confidence intervals for AUC0-t, AUC0-∞ and Cmax were within acceptance range recommended by United States Food and Drug Administration (FDA). CONCLUSIONS: Results demonstrate that the test formulation of oxycodone HCl ER tablets is bioequivalent to marketed OxyContin® reference formulations in Canada and USA, when administered both under fasted and fed conditions. Additionally, oxycodone HCl ER tablets were well tolerated as a single oral dose when administered to healthy adult subjects under fasted and fed conditions.

A Review of the Pharmacokinetics of Levothyroxine for the Treatment of Hypothyroidism.

Thyroxine hormone has been recognised since the early part of the nineteenth century and levothyroxine has been available since the mid-nineteenth century as a replacement for deficient thyroid hormones. While levothyroxine remains the staple treatment for hypothyroidism even to this day, its optimal use can be challenging. As is often the case with older drugs, the pharmacokinetics of levothyroxine is often under-appreciated or misunderstood and many factors influence the optimal dosing of levothyroxine. This article will review the pharmacokinetics of levothyroxine in the treatment of hypothyroidism and highlight major concepts that should aid both clinicians and researchers.

Impact of Tesamorelin, a Growth Hormone-Releasing Factor (GRF) Analogue, on the Pharmacokinetics of Simvastatin and Ritonavir in Healthy Volunteers.

The potential impact of tesamorelin on CYP3A activity was investigated by examining its effect on the pharmacokinetics of simvastatin and ritonavir. In two randomized, two-way crossover studies, subjects were administered 2 mg tesamorelin on Days 1-7 with 80 mg simvastatin or 100 mg ritonavir co-administered on Day 6 (Treatment A), and a single dose of simvastatin or ritonavir alone on Day 6 (Treatment B). Pharmacokinetic samples were collected on Day 6 to measure simvastatin, ritonavir and tesamorelin plasma concentrations. For simvastatin, A/B ratios of least squares geometric means and corresponding 90% confidence intervals (CIs) for AUC0-t , AUC0-inf and Cmax were contained within the usual no effect range of 80-125%. For ritonavir, ratios and 90% CIs for AUCs were within this acceptance range, but the lower CI for Cmax was 74.8%, suggesting a decreased rate of exposure. However, since the A/B ratios for AUCs and Cmax parameters were approximately 90%, these were minor decreases and no dose adjustment of ritonavir is required in the presence of tesamorelin. These studies showed that the impact of tesamorelin on CYP3A activity appears to be minimal, if any. Either medication may be co-administered with tesamorelin in patients without changing their original dosing regimen.

Pharmacokinetics of a new diclofenac sodium formulation developed for subcutaneous and intramuscular administration.

OBJECTIVE: To assess the relative bioavailability of diclofenac sodium hydroxypropyl ß-cyclodextrin (HPßCD) administered via the subcutaneous (s.c.) and intramuscular (i.m.) route versus Voltaren® i.m. and to evaluate the dose linearity and pharmacokinetics of the s.c. formulation at three dose levels. Safety and local tolerability were also assessed. MATERIALS AND METHODS: One single-dose, randomized, three-way, crossover relative bioavailability study and one linearity single escalating dose, randomized, three-way cross-over pharmacokinetic study were conducted at two different clinical sites. A total of 42 healthy male and female subjects participated in both studies. Subjects received 75 mg/ml diclofenac sodium HPßCD (i.m. and s.c.) and Voltaren® 75 mg/3 ml (i.m.) in Study 1 and 25, 50, or 75 mg/ml diclofenac sodium HPßCD (s.c.) in Study 2. RESULTS: Study 1 demonstrated bioequivalence of the s.c. test formulation with Voltaren® i.m. with respect to Cmax and AUC. Bioequivalence of the test i.m. with Voltaren® i.m. was also demonstrated (except the upper limit of the 90% confidence interval (CI) for Cmax which marginally exceeded the 80 - 125% range (125.78%)). Study 2 demonstrated that after s.c. administration of the test formulation, both Cmax and AUC are linearly related to the tested diclofenac doses. All tested doses were safe and locally well-tolerated with no serious adverse events reported. CONCLUSION: Bioequivalence of diclofenac HPßCD 75 mg/ml after s.c. and i.m. administration with Voltaren® i.m. was demonstrated, except for the marginal deviation in Cmax when comparing the i.m. test and Voltaren®. Linearity was also demonstrated for the three doses intended for marketing.