Review pubs.acs.org/molecularpharmaceutics
In Vitro Bioequivalence Approach for a Locally Acting Gastrointestinal Drug: Lanthanum Carbonate† Yongsheng Yang,*,‡ Rakhi B. Shah,‡ Lawrence X. Yu,§ and Mansoor A. Khan‡ ‡
Division of Product Quality Research, Office of Pharmaceutical Science, Food and Drug Administration, Life Science Building 64, 10903 New Hampshire Avenue, Silver Spring, Maryland 20993, United States § Office of Generic Drugs, Food and Drug Administration, 7519 Standish Place, Rockville, Maryland 20855, United States ABSTRACT: A conventional human pharmacokinetic (PK) in vivo study is often considered as the “gold standard” to determine bioequivalence (BE) of drug products. However, this BE approach is not always applicable to the products not intended to be delivered into the systemic circulation. For locally acting gastrointestinal (GI) products, well designed in vitro approaches might be more practical in that they are able not only to qualitatively predict the presence of the active substance at the site of action but also to specifically assess the performance of the active substance. For example, lanthanum carbonate chewable tablet, a locally acting GI phosphate binder when orally administrated, can release free lanthanum ions in the acid environment of the upper GI tract. The lanthanum ions directly reach the site of action to bind with dietary phosphate released from food to form highly insoluble lanthanum−phosphate complexes. This prevents the absorption of phosphate consequently reducing the serum phosphate. Thus, using a conventional PK approach to demonstrate BE is meaningless since plasma levels are not relevant for local efficacy in the GI tract. Additionally the bioavailability of lanthanum carbonate is less than 0.002%, and therefore, the PK approach is not feasible. Therefore, an alternative assessment method is required. This paper presents an in vitro approach that can be used in lieu of PK or clinical studies to determine the BE of lanthanum carbonate chewable tablets. It is hoped that this information can be used to finalize an in vitro guidance for BE studies of lanthanum carbonate chewable tablets as well as to assist with “in vivo” biowaiver decision making. The scientific information might be useful to the pharmaceutical industry for the purpose of planning and designing future BE studies. KEYWORDS: bioavailability, bioequivalence, locally acting GI drugs, dissolution, lanthanum carbonate, phosphate binding
■
INTRODUCTION BE studies are essential for development and approval of generic drugs. At certain stages of the development and approval process of even new drugs, the BE studies also play an important role.1 BE is defined in 21 CFR 320.1 as “the absence of a significant difference in the rate and extent to which the active ingredient or active moiety in pharmaceutical equivalents or pharmaceutical alternatives becomes available at the site of drug action when administered at the same molar dose under similar conditions in an appropriately designed study.”2 Approaches for determination of BE may vary with the route of administration and whether these products have systemic or locally acting implications. The regulation 21 CFR 320.24(b) provides a list of in vivo and in vitro methods to establish BE in descending order of preference: (1) in vivo studies in humans comparing drug/ metabolite concentrations in an accessible biological fluid, (2) in vivo testing in humans of an acute pharmacological effect, (3) controlled clinical trials in humans to establish safety and efficacy, (4) in vitro methods, and (5) any other approach deemed adequate by FDA.3 One or more of these approaches might be used to demonstrate BE. For example, the BE of solid oral dosage forms intended for systemic delivery is established by in vivo PK This article not subject to U.S. Copyright. Published 2012 by the American Chemical Society
studies with a support of comparative in vitro dissolution data. This approach has been successfully applied to a large number of drug products.4 However, the above approach is considered insufficient for demonstration of BE of locally acting GI drugs due to the fact that there is little or no relevance of PK data to drug delivery to the local site(s). For drugs whose site of action is the gastrointestinal (GI) tract, determination of bioequivalence is more complicated as local drug concentrations cannot be measured directly. Therefore, it is a challenging issue for both the pharmaceutical industry and the regulatory agency to determine the BE of locally acting GI drugs. The guidance on bioavailability and bioequivalence drafted by Committee of Proprietary Medical Products (CPMP) of the European regulatory authorities stated that “for medicinal products not intended to be delivered into the general circulation, the common systemic bioavailability approach cannot be applied.”5 A set of draft guidances on locally acting GI drug products have been developed by FDA over the last several years to provide recommendations to sponsors to meet statutory and regulatory Received: Revised: Accepted: Published: 544
September 13, 2012 December 5, 2012 December 18, 2012 December 18, 2012 dx.doi.org/10.1021/mp300517p | Mol. Pharmaceutics 2013, 10, 544−550
Molecular Pharmaceutics
Review
requirements.6−9 Generally, FDA addresses the issue on a case by case basis as outlined by the drug-specific guidance. Therefore, it is necessary to identify the key scientific principles for consistent and efficient identification of bioequivalence methods for locally acting GI drugs. The objective of this review article is to use lanthanum carbonate chewable tablet as an example to demonstrate that the in vitro approaches can be used to replace the conventional human pharmacokinetic in vivo studies in assessing the BE of locally acting GI drugs.
numbers of subjects to detect product differences.1 A dose-scale approach to assess BE has been used to estimate delivered dose of the test and reference products.12 Clinical Trials. Currently, it is suggested that, for some locally acting GI drugs, comparative clinical trials be conducted to demonstrate bioequivalence. Such studies need to show that the test product is equivalent to the reference product and also effective as compared to placebo. Comparative clinical studies are very expensive and can often be insensitive to formulation differences. Therefore, clinical bioequivalence studies are used only when any other approaches are deemed unsuitable. There are multiple guidance documents available which could be used as a guide to conduct such studies.13 In Vitro Studies. In vitro studies sometimes have more advantages than human PK in vivo studies in demonstrating BE of some solid oral dosage forms.14 When common approaches to the assessment of bioequivalence and pharmaceutical equivalence are not applicable, as is the case for complex drug products and locally acting drugs, scientific challenges might present barriers to the development and approval of generic drugs. Locally acting GI drugs present unique challenges to conduct PK studies to determine BE since the plasma concentrations are often undetectable. Also measurements at the site of action are often not possible if the drugs exert their effect on mucosal lining in the GI tract. In such instances, in vitro dissolution and/or in vitro efficacy study become useful for determination of BE. In general, for locally acting GI drugs in vitro dissolution studies can directly assess the rate and extent of delivery of the drug at the site of action since the studies focus on comparative drug release from the two products provided it reflects in vivo dissolution profile. Some GI acting drugs are formulated to target different regions of the GI tract, often via coatings that lead to pH dependent dissolution. Comparative dissolution testing at different pH could demonstrate that test and reference products are targeting the same region of the GI tract. Therefore, more attention should be focused on the selection of dissolution testing condition, especially pH levels which are generally recommended in a range of GI pH. When BE cannot be determined by dissolution study only, an in vitro efficacy study is preferred in order to fully determine BE. Application of the scientific basis of the BCS would suggest that a high solubility drug in a rapidly dissolving formulation with no excipient effect on product performance might be eligible for a biowaiver.15
■
METHODS TO ESTABLISH BE Pharmacokinetic (PK) Studies. This is a most widely used approach to determine the BE of a systemically acting drug product. PK studies measure the rate and extent of drug absorbed into systemic circulation. The rate and extent of drug absorption is compared by comparing Cmax (maximum plasma concentration) and AUC0−t (area under the curve from time 0 to last sampled time point) and/or AUC0−∞ (area under the curve from time 0 to extrapolated to time infinity). Since the two products being compared contain the same active ingredient, the differences between products can only result from differences in formulation performance much earlier in the absorption process. By comparing PK results we make a conclusion as to whether there is a significant difference in formulation performance or not. As the objective of bioequivalence testing is to evaluate formulation performance as reflected in changes in Cmax and AUC, it is clear that the connection of PK to product quality is the same regardless of the site of action since it is not always possible to measure the drug at site of action. It is assumed that there exists a predetermined relationship between the drug at the site of action and in the systemic circulation. Generally a crossover design is used to conduct a PK comparison study; however, for highly variable drugs some other designs might be warranted.10 For some locally acting drugs, such as those acting in the GI tract, its absorption in the systemic circulation might be very low or negligible, and hence it is not always possible to conduct a comparative PK study to determine BE. PK studies of locally acting drugs provide little or no information on the in vivo fate of the therapeutic moiety at its target site, although they might be useful from a safety perspective. When plasma levels can be used to determine the product effectiveness, PK studies are useful in determination of significant differences/similarities between test and reference listed products. In cases where there is no or minimum connection between plasma concentration and efficacy, PK studies are not very useful in determination of BE. Another concern about PK studies on locally acting GI drugs is that drug may be able to reach the site of action without entering systemic circulation. In such instances some other approaches discussed below might become useful. Pharmacodynamic Studies. Pharmacodynamic or pharmacological effects studies are useful in cases when a PK study could not be used to determine BE. For locally acting drugs, when the site of action does not involve any systemic drugs and when the drug absorption is too low to determine PK parameters, such an approach can be used with proper justifications. Establishment of a dose−response relationship is key to use this approach for determination of BA or BE.1 The BE study is usually conducted in the region where the effect can differentiate between the test and the reference drug product effects.11 If a BE study is conducted near the plateau of response, it might be insensitive to differences between the test and reference products. This consequently requires increased
■
LANTHANUM CARBONATE Lanthanum is used to treat hyperphosphatemia in patients with kidney disease.16,17 High levels of phosphate in the blood can cause bone problems. Lanthanum is in a class of medications called phosphate binders. Currently approved lanthanum medication includes Fosrenol chewable tablets. It contains lanthanum carbonate salt, which works by dissociating in the acid environment of the upper GI tract to release lanthanum ions, which binds dietary phosphate to form an insoluble lanthanum phosphate complex, which is then eliminated via feces.17,18 Thus site of action for this drug lies in the GI tract. Moreover, its oral absorption is extremely low with a BA of less than 0.002%.18,19 Thus a conventional PK approach is not feasible to determine BE for a generic drug product. A series of studies including hardness test, disintegration test, dissolution test, and phosphate binding studies were conducted to evaluate the feasibility of using these in vitro techniques to comparatively evaluate reference and test products. 545
dx.doi.org/10.1021/mp300517p | Mol. Pharmaceutics 2013, 10, 544−550
Molecular Pharmaceutics
Review
Table 1. Hardness of Lanthanum Carbonate Tablets (n = 10, Mean ± SD) hardness (kp)
ref
test A
test B
test C
test D
17.9 ± 1.3
17.6 ± 1.2
11.8 ± 1.1
31.8 ± 1.7
22.7 ± 1.5
Table 2. Disintegration Time of Lanthanum Carbonate Tablets in 0.1 N HCl (n = 6, Mean ± SD) time (h)
ref
test A
test B
test C
test D
4.25 ± 0.38
0.67 ± 0.02
4.11 ± 0.35
6.17 ± 0.15
3.96 ± 0.04
Hardness Test. The hardness of one reference and four test drug products with the strength of 1000 mg was evaluated. Ten tablets of each drug product were tested by using a VK 200 tablet hardness tester (Varian Inc., Cary, IN). A large variation was also observed in the hardness of lanthanum carbonate tablets, with some tablets showing excessive tablet hardness of higher than 20 kp (Table 1). In Vitro Disintegration Test. For the study, USP disintegration tester was used with 750 mL of 0.1 N HCl. The temperature of the medium was maintained at 37 °C. Disintegration studies were conducted for one reference and four test drug products. Disintegration data are summarized in Table 2. It was observed that test A product had significantly lower disintegration time as compared to other test products with respect to the reference product. Although this has not been used widely to compare pharmaceutical equivalence, such differences could be meaningful if the products show differences in the performance. To study this further, drug release studies from intact and crushed tablets were undertaken, which are described in the sections below. In Vitro Dissolution Studies. In vitro dissolution studies could directly assess the rate and extent of delivery of the lanthanum at the site of action. Lanthanum carbonate, practically insoluble in water, has a pH dependent solubility profile with poor solubility at higher pH and good solubility in acidic pH.20 The formulation, being a chewable tablet, does not contain any disintegrating agent. The chewing process of patients could help to release the drug, which then can become available at the site of action. Occasionally, some patients might swallow the whole lanthanum carbonate tablet instead of chewing as needed. Hence, it is useful to determine drug release from both whole and crushed tablets. In an effort to simulate the chewing condition, tablets were crushed using a mortar and pestle to very small uniform pieces, but not ground. It is important to determine the dissolution profile at various pH conditions which simulate GI tract conditions. Dissolution media with pH 1.2, 3.0, 4.5, and 6.8 were selected for conducting drug release studies of lanthanum carbonate chewable tablets. Selection of the dissolution apparatus and test conditions is important in determining dissolution of chewable tablets. Maintenance of sink condition for an extremely low aqueous soluble drug such as lanthanum carbonate should be considered. For lanthanum carbonate chewable tablets, the goal was to develop a comparative dissolution test for the reference as well as the test products. For the study, USP apparatus II (paddle) was selected with 900 mL of dissolution media (0.1 N HCl, pH 3.0, 4.5, and 6.8 buffers). Phosphate containing dissolution media were not used as the drug binds to phosphate to form an insoluble complex, thus retarding dissolution. Therefore, acetate and borate buffers were used. The paddle was stirred at 50 rpm, and the temperature of the dissolution media was maintained at 37 °C. A validated
complexometric titration with EDTA solution was used to analyze the dissolution samples and determine the concentration of lanthanum. Comparative dissolution studies were conducted for one reference and four test products at strength of 1000 mg. The dissolution was also conducted for the fraction of less than 200 μm which was generated from the crushed tablets by sieving it through USP sieve in order to check the uniformity of crushed tablet and the consistence of tablet crushing process. The similarity factor ( f 2) was calculated by using mean dissolution profiles.15 Dissolution profiles for whole and crushed tablets for reference and test drug products in 0.1 N HCl for 1000 mg strength are shown in Figure 1. As evident, the dissolution from
Figure 1. Dissolution profiles of reference and test lanthanum carbonate chewable tablets of 1000 mg strength in 0.1 N HCl for (A) whole and (B) crushed tablets (n = 6).
crushed tablets was significantly faster and higher as compared to whole tablets in all cases. Similar profiles were obtained for other pH media where a similar trend was observed (Figures 2−4). Drug release in pH 6.8 buffer was significantly lower 50 whereas the data showed differences in the products when the 546
dx.doi.org/10.1021/mp300517p | Mol. Pharmaceutics 2013, 10, 544−550
Molecular Pharmaceutics
Review
Figure 2. Dissolution profiles of reference and test lanthanum carbonate chewable tablets of 1000 mg strength in pH 3.0 medium for (A) whole and (B) crushed tablets (n = 6).
Figure 4. Dissolution profiles of the tablet fraction of less than 200 μm and the crushed tablet in pH 3.0 medium for (A) test A, (B) test D, and (C) reference (n = 6).
Table 3. The Similarity Factor (f 2) in pH 3.0 Medium for the Fraction of
