Biorelevant Dissolution Models for a Weak Base To Facilitate

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Biorelevant Dissolution Models for a Weak Base to Facilitate Formulation Development and Overcome Reduced Bioavailability Caused by Hypochlordyria or Achlorhydria Dawen Kou, Sudharsan Dwaraknath, Yannick Fischer, Daniel Nguyen, Myeonghui Kim, Hiuwing Yiu, Preeti Patel, Tania Ng, Chen Mao, Matthew Durk, Leslie Chinn, Helen Winter, Larry Wigman, and Peter Yehl Mol. Pharmaceutics, Just Accepted Manuscript • DOI: 10.1021/acs.molpharmaceut.7b00593 • Publication Date (Web): 23 Aug 2017 Downloaded from http://pubs.acs.org on August 24, 2017

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Molecular Pharmaceutics

Biorelevant Dissolution Models for a Weak Base to Facilitate Formulation Development and Overcome Reduced Bioavailability Caused by Hypochlordyria or Achlorhydria Dawen Kou*†, Sudharsan Dwaraknath||, Yannick Fischer¶, Daniel Nguyen†, Myeonghui Kim#, Hiuwing Yiu†, Preeti Patel†, Tania Ng†, Chen Mao†, Matthew Durk‡, Leslie Chinn§, Helen Winter§, Larry Wigman†, and Peter Yehl† †

Small Molecule Pharmaceutical Sciences, ‡Drug Metabolism and Pharmacokinetics, §Clinical Pharmacology, Genentech Inc., 1 DNA Way, South San Francisco, CA 94080, United States || Current Address: Department of Chemistry, University of Illinois at Urbana-Champaign, 505 S Mathews Ave, Urbana, IL 61801, United States ¶ Current Address: FHNW University of Applied Sciences Northwestern Switzerland, School of Life Sciences, Gründenstrasse 40, 4132 Muttenz, Switzerland # Current Address: Pfizer Korea, Pfizer Tower, 110, Toegye-ro, Jung-gu, Seoul, 04631, Korea ABSTRACT In this study, two dissolution models were developed to achieve in vitro-in vivo relationship for immediate release formulations of Compound-A, a poorly soluble weak base with pH-dependent solubility and low bioavailability in hypochlorhydric and achlorhydric patients. The dissolution models were designed to approximate the hypo-/achlorhydric and normal fasted stomach conditions after ingesting a glass of water with the drug. The dissolution data from the two models were predictive of the relative in vivo bioavailability of various formulations under the same gastric condition, hypo/achlorhydric or normal. Furthermore, the dissolution data were able to estimate the relative performance under hypo-/achlorhydric and normal fasted conditions for the same formulation. Together, these biorelevant dissolution models facilitated formulation development for Compound-A by identifying the right type and amount of key excipient to enhance bioavailability and mitigate the negative effect of hypo-/achlorhydria due to drug-drug interaction with acid reducing agents. The dissolution models use readily available USP apparatus 2, and their broader utility can be evaluated on other BCS 2B compounds with reduced bioavailability caused by hypo-/achlorhydria.

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KEYWORDS: biorelevant dissolution, poorly soluble weak bases, pH-dependent solubility, hypochlorhydria/achlorhydria, acid reducing agent (ARA), drug-drug interaction (DDI), Biopharmaceutics Classification System (BCS), in vitro-in vivo relationship/correlation (IVIVR/C)


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INTRODUCTION Dissolution of an orally dosed drug in the GI tract is a prerequisite for absorption, thus dissolution is a critical attribute that can affect the bioavailability and pharmacokinetics (PK) of a drug product. Dissolution testing plays important roles in the development and commercialization of oral drug products. For late stage development and marketed products, it is routinely used as a quality control (QC) test for product and process consistency at lot release and during its shelf-life. QC dissolution uses standardized USP apparatus under sink conditions, in which the drug solubility is ≥ 3x of the dissolved concentration. Commonly used QC dissolution media include USP simulated gastric fluid (SGF) or 0.1 N HCl, pH 4.5 acetate buffer, and USP simulated intestinal fluid (SIF) or pH 6.8 phosphate buffer 1. If necessary, surfactants are added in the media to increase solubility and achieve sink conditions 2. However, QC dissolution conditions and results may or may not reflect the GI tract conditions or relate to the performance of the dosage form in vivo. Dissolution testing also plays a critical role in assessing various formulations during early development and establishing a link to in vivo performance. The primary purpose of dissolution here is to relate to in vivo absorption and not for QC testing. Biorelevant dissolution aims to mimic the physiological conditions of the target population as much as possible. Non-sink conditions are acceptable and could occur for formulations that do not achieve adequate solubility. Biorelevant dissolution methods are often different from QC dissolution methods, although in some cases the same method can serve both purposes. Qualitatively, biorelevant dissolution should provide the correct rank order for different formulations and/or processes, also known as in vitro-in vivo relationship (IVIVR). Furthermore, it is desirable to establish quantitative in vitro-in vivo correlation (IVIVC) between dissolution and absorption data as defined by FDA guidelines 3. While IVIVC is not uncommon for extended release formulations, IVIVC for immediate release formulations has been a challenge with few reported examples 4. Various biorelevant dissolution media, e.g. FaSSGF, FaSSIF and FeSSIF, including several versions, have been developed in the last 20 years 5-7. They have been widely used and found to more closely resemble gastric and intestinal fluids in healthy human adults than media typically used in QC dissolution. The biorelevant media available to date cover the most common gastrointestinal conditions but are not intended for every possible scenario, e.g. conditions in which the stomach pH is outside of its typical range. Non-compendial systems have also been developed to study drug dissolution and absorption, such as TIM-1 8-9, artificial stomach and duodena model (ASD) 10-12, gastrointestinal simulator (GIS) 13-15, and µFlux 16. Most of these systems utilize two compartments (ASD and µFlux) or multiple compartments (TIM-1 and GIS) to mimic the stomach and part of, or the entire small intestine. Some include a second phase (an organic solvent or a membrane) to simulate absorption in the small intestine. All devices are either custom fabricated in individual labs or are specialized products, which may have limited their usage in drug product development. There is a need for dissolution models that are both biorelevant and can be easily performed on standard USP apparatus in general dissolution labs to facilitate formulation development. Physiologically based pharmacokinetic (PBPK) modeling and simulation for in vivo drug absorption with commercially available and/or proprietary software are being increasingly utilized by the industry and Health Authorities 17. PBPK modeling and simulation generally rely on default physiological parameters and input of compound specific physicochemical and pharmaceutics properties. Although it is possible to simulate the effects of various GI conditions on dissolution and absorption using software, in vitro dissolution of various formulations can provide more direct input for PBPK modeling. 3 ACS Paragon Plus Environment


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In addition to in vitro dissolution studies and in silico software simulation, in vivo animal studies are often used for formulation screening 18-20, which add time and cost to product development. Although dissolution methods may be modified after in vivo data are available to achieve IVIVR/C retrospectively, it is more challenging but more desirable to have clinically predictive dissolution and/or simulation models prospectively to guide formulation development prior to conducting in vivo studies. Many pharmaceutical compounds are weak bases with pH dependent solubility. The solubility is higher at low acidic pH in the stomach, but drops significantly as pH goes up to the mildly acidic to neutral range in the small intestine. The variation in stomach pH among different subjects or even the same subject at different times can be a significant source of variability in absorption and PK. In certain patient populations, the stomach is hypochlorhydric or achlorhydric (low or no hydrochloric acid) due to age, disease conditions, or intake of acid reducing agents (ARAs) such as proton pump inhibitors (PPIs) and H2-receptor antagonists (H2RAs) 21. Drug dissolution and bioavailability can be severely impaired under such conditions. ARAs are the most commonly prescribed medications in North America and Western Europe 22, and ARA-induced hypo-/achlorhydria is a common source of pharmacokinetic drugdrug interactions (DDI). If the ARA effect is not sufficiently mitigated, it can lead to the clinical label excluding the use of ARAs as co-medications or adjusting dosages in the presence of ARAs. Both scenarios are undesirable for patients because they limit the addressable population and increase the dosing complexity and risk of non-compliance. Compound-A is a clinical stage small molecule drug being developed by Genentech. Its key physicochemical properties are summarized in Table 1. Figure 1 shows a highly pH-dependent solubility curve of Compound-A. The solubility drops exponentially as pH increases from pH 2 to pH 5. Based on its high permeability and low solubility, Compound-A is considered a Biopharmaceutics Classification System (BCS) class 2 compound and in the subclass 2B (basic) 23-24. Table 1. Key physicochemical properties of Genentech Compound-A pKa (base) Log P Permeability (MDCK, A-B) Aqueous solubility

5.0, 3.7, and 1.1(measured) 3.3 15.1 x 10-6 cm/s 35.9 mg/mL at pH 2.3 0.001 mg/mL at pH 5.0 0.013 mg/mL in FaSSIF 0.018 mg/mL in FeSSIF

Capsules containing neat drug substance of Compound-A have shown poor bioavailability in Phase 1 clinical study in healthy volunteers with concomitant ARA use. A substantial portion of the target population for Compound-A takes ARAs, which will decrease the absorption of Compound-A. Therefore, it is critically important to develop formulations that can mitigate the hypo-/achlorhydria effect caused by ARAs and enhance the bioavailability of Compound-A. The objective of this study was to develop dissolution models to relate to in vivo performance of different formulations (IVIVR) for Compound-A. These dissolution models used USP apparatus 2 and took into account the physicochemical properties of the compound, the dose, the main site of in vivo dissolution, relevant physiological conditions of the target population, and water intake in clinical trial procedures. The models were used to develop various formulations to increase the bioavailability of Compound-A and reduce the elevated stomach pH effect. Based on the dissolution data, certain formulations were further developed and tested in dog PK studies to confirm the in vitro dissolution 4 ACS Paragon Plus Environment

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predictions. Subsequently, a lead formulation was selected for testing in a human relative bioavailability (RBA) study. 100 10

Concentration (mg/mL)

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1 0.1 0.01 0.001

0.0001 2

3

4

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6 pH

7

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Figure 1. The aqueous solubility profile of Compound-A as a function of pH. The dashed line represents theoretical values calculated from its pKa using the Henderson-Hasselbalch equation. The squares are experimentally measured values.

EXPERIMENTAL SECTION Materials. The drug substance or active pharmaceutical ingredient (API) of Compound-A was a crystalline free base from Genentech (South San Francisco, CA). Fumaric acid (FA) was from Bartek (Stoney Creek, ON, Canada), citric acid from EMD Millipore (Billerica, MA), and succinic acid from J.T. Baker (Avantor, Center Valley, PA). Acetonitrile was from J.T. Baker. Ammonium formate, formic acid, and HCl were from Sigma/Aldrich (St. Louis, MO). All chemicals were ACS or HPLC/GC grade. Purified water was obtained from a Millipore Milli-Q unit. FaSSIF powder was purchased from biorelevant.com (London, UK). A number of tablet formulations were developed at Genentech and evaluated in dissolution studies. The formulations contained the API and citric acid, succinic acid, or fumaric acid as functional excipients to modify the transient pH environment during dissolution. Other excipients included fixed amounts of lactose, croscarmellose sodium, and magnesium stearate, as well as adjustable amounts of microcrystalline cellulose to compensate for the various percentage of fumaric acid and keep tablet weight the same for the different formulations. None of these other common excipients had pH modulating effects on dissolution or bioavailability. Capsules containing API only and a tablet formulation without any acidic modifier were used as comparators. In addition, mesylate salt of the free base API was tested as an alternative to the free base formulations containing acidic modifiers. Dissolution Models. Two dissolution models were developed to mimic a hypo-/achlorhydric stomach and a normal fasted stomach after taking a glass of water (240 mL).



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Dissolution Model for Hypo-/Achlorhydric Stomach (D-H/A). This model evaluated 500 mL of pH 4.5 dilute HCl and water as dissolution media at 37 ºC to mimic the hypo-/achlorhydric stomach environment. A USP Dissolution Apparatus 2 was used with a paddle speed of 75 rpm. Since a minimum volume of 300 mL is needed for a USP apparatus 2 to work as intended, 500 mL of dissolution media was used in this study. To compensate for the larger volume used in the vessel (500 mL) than in the stomach (250 mL), the dose used for in vitro dissolution was doubled. The clinical dose was 200 mg unless noted otherwise. To achieve the same dose/volume ratio as 200 mg/250 mL, a 400 mg dose in 500 mL dissolution media was used. Samples were pulled at predetermined time points up to 60 minutes, and analyzed by HPLC. Dissolution Model for Normal Fasted Stomach after Water Intake (D-WI). This model used 500 mL of pH 2.4 HCl solution to mimic the normal stomach environment after intake of a standard glass of water. A USP Dissolution Apparatus 2 was used with the paddle speed at 75 rpm. The same dose/volume approach was used as the D-H/A model. Samples were taken at predetermined time points up to 60 minutes, and analyzed by HPLC. Two-Stage Dissolution. The two models above could be extended to a two-stage method, starting with D-H/A or D-WI as the first stage, followed by adding 500 mL of FaSSIF (2x) at 30 minutes to mimic gastric transfer to the small intestine as the second stage. Dissolution Equipment. Several USP Dissolution Apparatus 2 with similar functionalities were utilized, including Agilent model 708-DS with 810 Peristaltic pump and 8000 dissolution sampling station (Agilent Technologies, Santa Clara, CA) and Distek models Symphony 7100 or Evolution 6100 equipped with syringe pumps and Evolution 4300 autosamplers (Distek, Inc. North Brunswick, NJ). Distek ezfill 4500 was used for dissolution media preheating, deaeration, and automated dispensing. Automated sampling of 1.5 mL was performed at preset time points, with a 10 µm filter for each sampling line. In addition, a pH meter with pH/ATC liquid filled combination electrode (Accument AB150, Fisher Scientific, Hampton, NH) was used to measure the pH of dissolution media before, during, and after dissolution. Sinkers (part number CAPWST-23, Sotax style capsule sinker from QLA, Telford, PA) were used to prevent the capsules from floating. No sinkers were used for the tablets. HPLC Instrument and Method. Agilent 1200 HPLC systems were used for sample analysis, with Empower 3 chromatography software (Waters Corporation, Milford, MA) for instrument control, data acquisition, and data processing. The HPLC method used an Agilent Poroshell EC-C18 column (150 mm x 3.0 mm, 2.7 µm particle size), an isocratic mobile phase of 35:65=10 mM ammonium formate at pH 3.7: acetonitrile with a flow rate of 0.6 mL/min, a UV detector at 245 nm, and an injection volume of 1 µL. The column temperature and autosampler temperature were 40ºC and ambient, respectively. Software Simulation. GastroPlus software version 9.0 (Simulation Plus, Lancaster, CA) was used for absorption modeling and simulation. In addition to the parameters listed in Table 1, particle size distribution for a representative API lot (dv10 = 5.0 µm, dv50 = 12.8 µm, dv90 = 27.1 µm), precipitation time of 500 minutes (assuming no precipitation), and the default human fasted state physiological parameters in GastroPlus were used for the simulation. Dog PK Studies. The dog gastric pH has been reported to be highly variable and generally higher than the human stomach pH. Therefore dogs are typically pre-treated with pentagastrin, an analog of gastrin to stimulate gastric acid secretion to achieve a lower and more consistent gastric pH 25-26, or with famotidine to achieve an elevated pH due to the ARA effect 27. Male beagle dogs (n=5 per group) were used in two PK studies for several selected formulations for Compound-A. Some groups were pretreated with famotidine at 40 mg/dog by oral administration approximately 180 minutes (±10 min) before test 6 ACS Paragon Plus Environment

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compound dosing, while other groups were pretreated with pentagastrin at 6 µg/kg by intramuscular injection approximately 30 minutes (±2 min) before test compound dosing. In the first study, each group was dosed with one of the formulations containing 200 mg of free base API and various amounts of fumaric acid. In the second study, famotidine pretreated dogs were dosed with a formulation containing mesylate salt and the best formulation from the first study. About 20 mL of water was given to the animal following each dosing administration. Water intake was not restricted during the studies. Blood samples were collected from each dog before and after dosing at pre-determined time points up to 24 hours. The arithmetic means of maximum observed plasma concentration (Cmax) and area under the concentrationtime curve (AUC) for each group were calculated. The stomach pH of each dog was not measured, but several studies using the same doses of pentagastrin or famotidine reported that 30 minutes after pentagastrin treatment the average stomach pH decreased to 1-2 or 2-3 and lasted for 1 hour 18-19, and that 1-2 hours after famotidine treatment pH increased to ~ 7 and lasted for 4-5 hours 19-20. Human RBA Study. Thirty two healthy volunteers were enrolled in a single center, randomized, open-label, crossover clinical study to compare the bioavailability and PK profiles of an optimized tablet formulation and neat API in capsules under fasted conditions. The tablets were also tested under fed, fasted+ARA, and fed+ARA conditions. All doses were taken with 240 mL of potable water, with water permitted up to 1 hour before and 1 hour after dosing. The ARA dosed was rabeprazole twice daily (20 mg BID) for 3 days and then a single dose (20 mg) 2 hours prior to administration of Compound-A. Blood samples were collected from each volunteer before and after dosing at pre-determined time points up to 24 hours. The geometric Least Squares (LS) means of Cmax and AUC for each cohort were calculated to characterize plasma pharmacokinetics. The details of the clinical study will be presented in another publication.

RESULTS Impact of Stomach pH on Absorption as Simulated by GastroPlus. Figure 2 shows a parameter sensitivity analysis (PSA) by GastroPlus of percentage of drug absorbed as a function of stomach pH, assuming no precipitation in the small intestine after gastric transfer. The simulation shows that the percentage absorbed drops quickly from 100% to 20% if the stomach pH increases from 2.8 to 4.2. The simulation result is consistent with the observed relative bioavailability of Compound-A API in capsules with and without the use of ARA as co-medication in the Phase 1 clinical study.



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Figure 2. GastroPlus simulation of percentage of Compound-A absorbed as a function of stomach pH Dissolution Profiles of Formulations Containing Different Acidic Excipients using the DH/A Model. In order to improve drug dissolution and bioavailability under the ARA induced hypo/achlorhydric conditions, three weak acids, citric acid, succinic acid, and fumaric acid, were evaluated as pH modifiers in three tablet formulations to lower the transient local pH during dissolution. The three weak acids are all solid and are generally recognized as safe pharmaceutical excipients. Each acid has two or more pKa values: 3.0 and 4.5 for fumaric acid; 3.1, 4.8, and 6.4 for citric acid; 4.2 and 5.6 for succinic acid. During dissolution, the weak acids provided a lower pH in the local microenvironment and in bulk solution. Figure 3 shows the dissolution profiles of the three formulations using the D-H/A model in pH 4.5 HCl to mimic the hypochlorhydric stomach. Dissolution of the formulation containing 30% fumaric acid was the fastest, followed by 30% citric acid, and 30% succinic acid, with the ending pH at 2.9, 3.0, and 3.5 respectively. Because fumaric acid enabled the fastest dissolution among the three acids tested, it was chosen as the acidic modifier for further development.


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100 Tablet formulation containing 20% of API and 30% of fumaric acid

90 80 70

Tablet formulation containing 20% of API and 30% of citric acid

60 %Dissolved

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50 40

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30 20 10 0 0

5

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Time (min)

Figure 3. Dissolution profiles of tablet formulations containing different acidic excipients using D-H/A model in pH 4.5 dilute HCl. Each data point is the mean ±SD (n=2). Dissolution Profiles of Formulations Containing Various Amounts of Fumaric Acid using the D-H/A Model. Figure 4 shows the profiles of tablet formulations containing 15% of API and 0%, 5%, 10%, or 15% FA dissolved in pH 4.5 HCl or water using the D-H/A model. The pH of pure water is 7, but may vary depending on the source. The DI water in our lab had a measured pH of 5.7. The dissolution profiles of the formulation with a stronger acidic modifier (15% FA) in pH 4.5 HCl and in water were superimposable. The formulation with a weaker acidic modifier (5% FA) dissolved slightly faster in pH 4.5 HCl than in water. For comparison, the 10% FA formulation was dissolved in pH 4.5 dilute HCl and in 5 mM pH 4.5 acetate buffer. Due to the buffering effect, dissolution in the acetate buffer was only about half of what was achieved in pH 4.5 HCl. The rate of dissolution increased quickly with increasing amounts of FA in the formulation. The 15% FA formulation dissolved rapidly with ~75% of Compound-A dissolved at 30 minutes and a final pH of 3.0, while the drug in the formulation without FA only dissolved ~2% with a final pH of 8.0.



Tablets containing 15% API and 15% FA, dissolved in pH 4.5 HCl (n=2)

100 90

Tablets containing 15% API and 15% FA, dissolved in water (n=3)

80


70 60 %Dissolved

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50 40

Tablets containing 15% API and 5% FA, dissolved in water (n=3)

30 Tablets containging 15% API and 10% FA dissolved in 5mM pH 4.5 acetate buffer (n=2)

20 10


0 0

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Figure 4. Dissolution profiles of tablet formulations containing Compound-A and various amounts of fumaric acid using the D-H/A model. A formulation was also dissolved in 5 mM pH4.5 acetate buffer for comparison. Each data point is the mean ±SD . Dissolution Profiles of the 15% FA and Mesylate Salt Formulations using the D-H/A Model. As a general strategy, salts of free base API can be used to increase aqueous solubility. The mesylate salt of the free base Compound-A was made as an alternative to formulations containing free base API and fumaric acid. Other salts were also considered but not used because they were highly hygroscopic and difficult to handle and process. Figure 5 shows that dissolution of the 15% FA formulation was faster and more complete than the mesylate salt formulation using the D-H/A model. The ratio of percentage dissolved at 45 minutes was 2.0 for the two formulations. In Vivo Performance of Different Formulations under Achlorhydric Conditions. Figure 6 shows the plasma concentration profiles of the 15% FA and mesylate salt formulations in dogs pretreated with famotidine. The Cmax and AUC ratios were 2.0 and 1.7 for these two formulations. Based on these data, the mesylate salt formulation was not further developed. The 15% FA formulation was selected as the lead formulation for the human RBA study to compare with capsules containing neat API used in the Phase 1 clinical trial.


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Tablet formulation containing 15% free base API and 15% FA Tablet formulation containing mesylate salt equivalent to 15% free base

100 90 80 70 % Dissolved

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30 Time (min)

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Figure 5. Dissolution profiles of 15% FA tablet formulation vs. mesylate salt formulation using the DH/A model with pH 4.5 dilute HCl. Each data point is the mean ± SD (n=2).

6 Tablets containing 15% free base API and 15% FA

5 Plasma Concentration (uM)

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Tablets containing mesylate API equivalent to 15% free base 4

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Figure 6. PK profiles of 15% FA tablet formulation vs. mesylate salt formulation in dogs pretreated with famotidine (an ARA). Each data point is the mean ± SD (n=5). 11 ACS Paragon Plus Environment


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IVIVR for Different Formulations under Hypo-/Achlorhydric Conditions. Table 3 is a summary of in vitro dissolution data of different formulations using the D-H/A model and in vivo relative bioavailability data in dogs pretreated with famotidine. The in vitro dissolution data correctly predicted which formulation would provide better bioavailability. The in vitro and in vivo data showed that adding the right amount of fumaric acid to the formulation dramatically improved the dissolution and bioavailability of Compound-A under hypo-/achlorhydric conditions. Table 2. Comparison of different formulations under the hypo-/achlorhydric condition: relationship between in vitro dissolution data and in vivo dog PK data Formulation A

B

In vitro dissolution in pH 4.5 HCl % disso. at 45 min A B A/B ratio 82.0 3.1 a 27

Tablets Tablets containing containing 15% 15% free base API free base API and and no FA 15% FA Tablets Tablets containing 65.8 46.0 1.4 containing 15% 15% free base API free base API and and 5% FA 10% FA Tablets Tablets containing 82.0 40.7 2.0 containing 15% mesylate salt free base API and equivalent to 15% 15% FA free base a dissolution in pH 4.5 HCl followed by a second stage in FaSSIF

In vivo PK in famotidine pretreated dogs Cmax (µM) AUC0-24 (µM*h) A B A/B A B A/B ratio ratio 4.62 0.20 24 43.9 8.39 5.2

2.2

12.6

2.62

1.91

1.4

21.3

14.0

1.5

2.2

1.2

4.22

2.13

2.0

34.8

20.8

1.7

2.0

1.6

Tmax (h) A B

Dissolution Profiles of Various Formulations Using the D-WI Model. Figure 7 shows the dissolution profiles of three tablet formulations containing 15% API and 0%, 10%, or 15% FA and capsules containing API only, using the D-WI model in pH 2.4 HCl. The dissolution profiles of the four formulations were well differentiated, and the ratios of % drug dissolved at 45 minutes were 100:84:56 for the 15% FA tablets, tablets with no FA, and API in capsules, respectively. On the other hand, in FaSSGF (pH 1.6), the same four formulations with and without fumaric acid all dissolved quickly in 15 minutes and completely within 30 minutes as shown in Figure 8.


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100 Tablets containing 15% API and 15% FA

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Tablets containing 15% API and 10% FA

% Dissolved

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Figure 7. Dissolution profiles of formulations containing various amounts of fumaric acid in D-WI model with pH 2.4 HCl. Each data point is the mean ± SD (n=3 for Tablets containing 10% FA, n=6 for the other formulations).

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Tablets containing 15% API and no FA

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60


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Figure 8. Dissolution profiles of formulations containing various amounts of fumaric acid in FaSSGF (pH 1.6). Each data point is the mean ± SD (n=3 for 15% FA tablets and API filled capsules; n=2 for the other formulations).



In Vivo Performance of Different Formulations under Normal Stomach Conditions. Figure 9 shows the plasma concentration profiles of the 10% FA and no FA formulations in pentagastrin pretreated dogs. Figure 10 shows the plasma concentration profiles of the 15% FA tablet formulation and capsules containing API only from the human RBA study. The AUC and Cmax of the 15% FA formulation cohort were approximately twice those of the capsules.

10 Tablets containing 15% API and 10% FA 9 Tablets containing 15% API and no FA 8 Plasma Concentration (uM)

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7 6 5 4 3 2 1 0 0

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24

Figure 9. PK profiles of tablet formulations containing 10% FA or no FA dosed in dogs pretreated with acid inducer pentagastrin. Each data point is the mean ± SD (n=5).


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900 800 15% FA Tablet Formulation

700 Plasma Concentration (ng/mL)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


API Filled Capsules 600 500 400 300 200 100 0 0

2

4

6

8

10

12

14

16

18

20

22

24

Time (hr)

Figure 10. PK profiles of 15% FA tablet formulation and API filled capsules dosed in healthy volunteers without pretreatment in the human RBA study. Each data point is the mean ± SD (n=15 for the tablet group, n=16 for the capsule group). IVIVR for Different Formulations under Normal Stomach Conditions. Table 3 is a summary of in vitro dissolution data of various formulations using the D-WI model and in vivo human and dog PK data under normal, fasted stomach conditions. The FA based formulations had higher percentage dissolved, in line with the higher in vivo bioavailability observed. Table 3. Comparison of different formulations under the normal stomach conditions: relationship between in vitro dissolution data and in vivo human and dog data Formulation A

B

In vitro dissolution in pH 2.4 HCl % disso. at 45 min A B A/B ratio 99.5 55.9 1.8

In vivo PK Study A

Tablets Capsules human a 535 containing containing ng/mL 15% API and API only 15% FA Tablets Tablets 97.0 84.2 1.2 dog b 9.12 containing containing µM 15% API and 15% API 10% FA and no FA a no pretreatment, human RBA study; b pretreated with pentagastrin

Cmax B 267 ng/mL

7.14 µM

A/B ratio 1.9

1.3

A

AUC0-24 B

2540 ng/mL*h

1480 ng/mL*h

106 µM*h

71.2 µM*h

Tmax (h) A B

A/B ratio 1.7

1.0

1.5

1.5

2.6

1.4



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IVIVR for the Same Formulation under Hypo-/Achlorhydric and Normal Conditions. Table 4 compares in vitro dissolution data of the same formulation using the D-H/A and D-WI dissolution models with relative bioavailability data in dogs and humans under hypo-/achlorhydric and normal conditions. The data show that, for each formulation, the ratio of percentage dissolved from the two dissolution models can be used to roughly estimate the relative in vivo performance under hypo/achlorhydric and normal conditions in dog and human studies. Table 4. Performance of the same formulations under hypo-/achlorhydric and normal conditions: relationship between in vitro dissolution data and in vivo human and dog data Formulation

In vitro dissolution % disso. at 45 min A: in B: in A/B pH 4.5 pH 2.4 ratio HCl HCl 82.0 99.5 0.82

In vivo PK Study A

Cmax B

A/B ratio

A

AUC0-24 B

A/B ratio

Tmax (h) A B

2540 0.74 1.0 1.0 Tablets human a 279 535 0.52 1880 containing ng/mL ng/mL ng/mL*h ng/mL*h 15% API and 15% FA Capsules 62.4 0.12 human b 7.3 106 0.07 171 570 0.30 4.0 1.5 7.8 d containing ng/mL ng/mL ng/mL*h ng/mL*h API only b Tablets 3.1 d 84.2 0.04 dog c 0.20 7.14 0.03 8.39 71.2 0.12 12.6 1.4 containing µM µM µM*h µM*h 15% API and no FA a human RBA study at 200 mg dose, A: pretreated with ARA rabeprazole, B: no pretreatment b human Phase 1 study at 100 mg dose, A: pretreated with ARA rabeprazole, B: no pretreatment; Same dose for dissolution data c dog study, A:pretreated with ARA famotidine, B: pretreated with acid inducer pentagastrin d dissolution in pH 4.5 HCl followed by a second stage in FaSSIF

DISCUSSION D-H/A Model for the Hypo-/Achlorhydric Stomach. Stomach is the first site of dissolution for weakly basic compounds, and the fluid in the fasted stomach has little extra buffer capacity beyond the inherent capacity of HCl 6. The buffer capacity is defined as the ability to resist pH change, and should not be confused with the presence or concentration of a classic buffer. The buffer capacity is especially low in the hypo-/achlorhydric stomach and consistent with elevated pH 28. The dissolved drug can cause the stomach pH to rise, and depending on the extent of the increase, it can impede further dissolution. On the other hand, better dissolution may be achieved by changing the transient microenvironment pH in the stomach to the desirable range using acidic modifiers in the formulation. Biorelevant dissolution models should allow for and reflect the pH change caused by the drug and excipients in the formulation. Various dissolution media have been reported in literature to mimic hypo-/achlorhydria, such as pH 3.0 HCl/NaCl 29, 50 mM pH 4.5 acetate buffer 30, pH 5.0 acetate buffer (unspecified concentration) 31, and pH 6.0 HCl 15, however, the rationales for these media have not been extensively discussed. A very recent paper investigated several media containing low concentration phosphate, maleate, or bicarbonate buffers at pH 5.0 and 7.0 to mimic hypochlorhydria and achlorhydria, which showed mixed results when compared with ex-vivo media and in vivo data, with a better fit under hypochlorhydria than achlorhydria 32. The general treatment goal of using ARAs is to achieve gastric pH ≥4 or 3, and the mean percentage of time that gastric pH is ≥ 4 or 3 in a 24-hour period is used to evaluate the efficacy of ARAs 33-34 . There are a number of ARA drugs with different efficacy at different doses for different treatment 16 ACS Paragon Plus Environment

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groups, with the reported 24-h mean pH for 5 different PPIs ranging from

Biorelevant Dissolution Models for a Weak Base To Facilitate

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