Bioavailability study of commercial sustained-release preparations of diclofenac sodium in gastrointestinal physiology regulated-dogs

Quabodepistat (OPC-167832), a Novel Antituberculosis Drug Candidate: Enhancing Oral Bioavailability via Cocrystallization and Mechanistic Analysis of Bioavailability in Two Cocrystals

Quabodepistat (code name OPC-167832) is a novel antituberculosis drug candidate. This study aimed to discover cocrystals that improve oral bioavailability and to elucidate the mechanistic differences underlying the bioavailability of different cocrystals. Screening yielded two cocrystals containing 2,5-dihydroxybenzoic acid (2,5DHBA) or 2-hydroxybenzoic acid (2HBA). In bioavailability studies in beagle dogs, both cocrystals exhibited better bioavailability than the free form; however, the extent of bioavailability of cocrystals with 2HBA (quabodepistat-2HBA) was 1.4-fold greater than that of cocrystals with 2,5DHBA (quabodepistat-2,5DHBA). Dissolution studies at pH 1.2 yielded similar profiles for both cocrystals, although the percent dissolution differed: quabodepistat-2HBA dissolved more slowly than quabodepistat-2,5DHBA. The poor solubility of quabodepistat-2HBA is likely the primary factor limiting dissolution at pH 1.2. To identify a dissolution method that maintains the bioavailability in beagle dogs, we performed pH-shift dissolution studies that mimic the dynamic pH change from the stomach to the small intestine. Quabodepistat-2HBA demonstrated supersaturation after the pH was increased to 6.8, while quabodepistat-2,5DHBA did not demonstrate supersaturation. This result was consistent with the results of bioavailability studies in beagle dogs. We conclude that a larger quantity of orally administered quabodepistat-2HBA remained in its cocrystal form while being transferred to the small intestine compared with quabodepistat-2,5DHBA.

Evaluation of Acid Tolerance of Drugs Using Rats and Dogs Controlled for Gastric Acid Secretion

We attempted to establish animal models to evaluate the effects of drug degradation in the stomach on oral bioavailability. In addition, we assessed the utilization of animal studies in determining the need for enteric-coated formulations. In order to control the gastric pH in rats and dogs, appropriate dosing conditions were investigated using pentagastrin and rabeprazole, which stimulate and inhibit gastric acid secretion. Using animals controlled for gastric acid secretion, the area under curve (AUC) ratios (AUC with rabeprazole/AUC with pentagastrin) of all compounds unstable under acidic conditions were evaluated. The AUC ratios of omeprazole and erythromycin, which are administered orally to humans, as enteric-coated tablets, were greater than 1.9 in the rats and dogs controlled for gastric acid secretion. On the contrary, the AUC ratios of clarithromycin, azithromycin, and etoposide (commercially available as a standard immediate-release form) were less than 1.3 each. In conclusion, in vivo models using rats and dogs were optimized to evaluate the effects of gastric acid on the oral bioavailability of drugs, and demonstrated that in vivo models can lead to a better understanding of the oral bioavailability, with respect to the formulation development.

Dosage form design and in vitro/in vivo evaluation of cevimeline extended-release tablet formulations

The objective of the present work is to develop an extended-release dosage form of cevimeline. Two types of extended-release tablets (simple matrix tablets and press-coated tablets) were prepared and their potential as extended-release dosage forms were assessed. Simple matrix tablets have a large amount of hydroxypropylcellulose as a rate-controlling polymer and the matrix is homogeneous throughout the tablet. The press-coated tablets consisted of a matrix core tablet, which was completely surrounded by an outer shell containing a large amount of hydroxypropylcellulose. The simple matrix tablets could not sustain the release of cevimeline effectively. In contrast, the press-coated tablets showed a slower dissolution rate compared with simple matrix tablets and the release curve was nearly linear. The dissolution of cevimeline from the press-coated tablets was not markedly affected by the pH of the dissolution medium or by a paddle rotating speed over the range of 50-200 rpm. Furthermore, cevimeline was constantly released from the press-coated tablets in the gastrointestinal tract and the steady-state plasma drug levels were maintained in beagle dogs. These results suggested that the designed PC tablets have a potential for extended-release dosage forms.

Design of Nanohydrogel-Incorporated Microcapsules for Appropriate Controlled-Release of Peptide Drugs

Biologically active peptides for therapeutic use have relatively short half-lives in general, requiring appropriate controlled-release systems for better therapy. Controlled release of peptides is, however, not as easy as that of conventional drugs because their large molecular size is much more dramatic in hindering the diffusion and release from polymeric devices. From this perspective, we have been developing two types of microcapsular devices containing new acrylate-based nanogels with a specific solute-permeability for delayed- or thermosensitive-release of peptide drugs. The microcapsule preparation was accomplished by an air suspension coating process. A nanogel-particle of acrylic terpolymer, ethyl acrylate-methyl methacrylate-2-hydroxyethyl methacrylate, was newly synthesized by emulsion polymerization to construct delayed-release microcapsules. By spray-coating the insulin-loaded lactose particles with the acrylic terpolymers, microcapsules showing a pH-independent delayed-release profile can be obtained. Oral administration of the microcapsules with the lag time of 6 hours to beagle dogs resulted in significantly reduced blood glucose concentration, leading to colon-specific insulin delivery with pharmacological availability of 5%. Meanwhile, poly(N-isopropylcarylamide) (p(NIPAAm)) nanogel-particles with a reversible temperature-dependent swelling property were prepared by dispersion polymerization to fabricate microcapsular membranes with thermosensitively changeable permeability. The microcapsules constructed by coating of drug-loaded CaCO(3) particles with a blend mixture of the p(NIPAAm) nanogels and ethylcellulose pseudo-latex exhibited an 'on-off' positively thermosensitive drug-release; the release rate was remarkably enhanced at higher temperatures possibly due to the formation of voids through the shrinkage of p(NIPAAm) nanogels in the membrane. A possible application of this type of microcapsules can be found in externally temperature-activated pulsatile peptide delivery.

Suitability of the cynomolgus monkey as an animal model for drug absorption studies of oral dosage forms from the viewpoint of gastrointestinal physiology

To determine the usefulness of the monkey as an animal model, which can predict in vivo performance of humans, the major gastrointestinal physiological parameters of this animal were evaluated. The pH of gastric juice collected by a fiberscope from the stomach in fasted cynomolgus monkeys showed a high acidity level, which ranged from 1.2 to 4.3. The gastric emptying time of oral dosage forms (solution, granules and tablets) showed that the larger size dosage forms seemed to be emptied more slowly, and three dosage forms were prolonged by feeding. The gastrointestinal agitation intensity of monkeys was estimated using controlled-release tablets of acetoaminophen, which showed a slow erosion rate. The in vivo release amount-time profiles of the tablet in fasted monkeys corresponded to their in vitro profiles with paddle agitation conditions of between 10 rpm and 50 rpm of the paddle method; this result was smaller than in dogs (100 rpm) but equivalent to that in humans (10 rpm). Further, the small intestinal transit time (SITT), estimated using a double marker method, ranged from 2.2 to 4.2 h in the fasting state and from 2.2 to 3.2 h in the fed state; the SITT was not significantly delayed by feeding. Comparison with the published data about dogs and humans showed these gastrointestinal physiological parameters of monkeys to be more similar to those of humans. Consequently, it is assumed that the monkey is useful as an animal model for bioavailability studies of oral dosage forms.

The effect of polyion complex formation on in vitro/in vivo correlation of hydrophilic matrix tablets

The aim of this study was to investigate the effects of polyion complex formation on in vivo performance of hydrophilic matrix tablets. Three kinds of controlled release theophylline tablets were prepared by direct compression using carboxymethyldextran (CMD), a mixture of CMD and [2-(diethylamino)ethyl]dextran (EA), and a mixture of dextran sulfate (DS) and EA. According to a conventional dissolution test, in vitro drug release profiles of these tablets were similar to each other. In vivo absorption profiles of theophylline after oral administration to beagle dogs, however, were quite different and were not consistent with in vitro release profiles. Thus, we applied a modified in vitro release test considering destructive forces. An excellent in vitro/in vivo correlation was obtained in the cases of CMD/EA- and DS/EA-tablets. The results suggested that the drug was released constantly in the overall gastrointestinal tract, and even in the colon. Then, hydrophilic matrices were characterized by swelling rate, matrix density and strength in a wet state. DS/EA-tablets showed limited swelling, higher density and a larger value of wet strength than the others. These findings indicated that polyion complex formation in gel layer contributes to prevent over-swelling and strengthen the wetted matrices.

Gastrointestinal transit of liquids in unfed cynomolgus monkeys

In this study, the gastric emptying rate and oro-caecal transit time of two liquid volumes (20 and 60 ml) were compared in unfed cynomolgus monkeys. First, the acetaminophen method was used to determine the gastric half-emptying time (t(50%)). The mean t(50%) from seven monkeys was 21.2 min for the 20-ml volume and 27.8 min for the 60-ml volume. This mean t(50%) in monkeys is similar to that reported previously in fasting humans. Next, the sulfasalazine-sulfapyridine method was used to determine median oro-caecal transit times for the 2 liquid volumes; these times were 2.5 h for the 20-ml volume and 2.3 h for the 60-ml volume, which are about 1.5 h shorter than previously reported transit times in humans. An increase in volume administered did not significantly change either the t(50%) or oro-caecal transit time. The data also show that variability in both t(50%) and oro-caecal transit time within each monkey is not as great as the large variability between monkeys. Consequently, cynomolgus monkeys are good model animals to use for studies on the gastric emptying of drug-containing liquids after fasting; however, analysis of results from bioavailability studies must compensate for differences in the oro-caecal transit time between monkeys and humans.

Influence of water soluble fillers in hydroxypropylmethylcellulose matrices on in vitro and in vivo drug release

The purpose of this study was to investigate the effect of fillers in gel-forming matrix on in vivo drug release after oral dosing. A further purpose was to predict the in vivo performance from in vitro dissolution test. Three controlled-release acetaminophen tablets containing hydroxypropylmethylcellulose (HPMC) with or without highly water soluble fillers, lactose or polyethylene glycol 6000 (PEG6000), were prepared. Water penetration into the matrix was enhanced by addition of fillers in the matrices, but the three tablets showed similar in vitro dissolution profiles, indicating that fillers in the HPMC matrices little affected the in vitro drug release. In contrast, the fillers in HPMC matrices did affect the in vivo performance in dogs. The absorption profile of HPMC matrix with PEG6000 was the fastest, followed by that with lactose and without water soluble filler, in that order. As the matrix with PEG6000 had a large amount of water and gelated a large portion of the matrix when in contact with water, the gel layer would be disintegrated by the gastrointestinal motility. It was found that dissolution of gel-forming HPMC matrices under mechanical stress by glass beads well correlated with the in vivo performance of the matrix, with little correlation by the conventional paddle method.

Technology to obtain sustained release characteristics of drugs after delivered to the colon

To determine the necessary technology by which sustained drug release is obtained after drug is delivered to the colon, two kinds of microcapsules were prepared and were filled in a pressure-controlled colon delivery capsule (PCDC). As a model drug 5-aminosalicylic acid (5-ASA) was used, because the target site of 5-ASA is the entire large intestine. 5-ASA was microencapsulated using a water-insoluble polymer, ethylcellulose (EC) or with pH-sensitive polymers, Eudragit L-100 or S-100 and encased in PCDC. The particle size of these microcapsules was around 800 microns and the loading efficiencies of 5-ASA were approximately 90%. In vitro dissolution tests were performed with the prepared microcapsules. The release rate of 5-ASA from the microcapsules was significantly prolonged as compared to 5-ASA powder, although there were no significant differences in the release rates between these microcapsules. By incorporating the 5-ASA microcapsules into PCDC, sustained release PCDCs for colon delivery were prepared and in vivo evaluation was performed using beagle dogs. As a fast release colon delivery system, PCDCs were prepared with 5-ASA powder suspended in suppository base. After oral administration of the test preparations to beagle dogs, plasma 5-ASA concentrations were measured and sustained release characteristics of 5-ASA from the test preparations were evaluated from the plasma 5-ASA concentration-time profiles. The first appearance time of 5-ASA into the systemic circulation after oral administration were 3 h for all the colon delivery preparations and it was thought that these test preparations were delivered to the colon. Both EC microcapsules and Eudragit S-100/RS-100 microcapsules in PCDC showed longer the mean residence time MRT, 8.2 +/- 0.6 h and 8.7 +/- 0.9 h, than Eudragit L-100/RS-100 microcapsules in PCDC where the MRT was 6.6 +/- 0.2 h. Since PCDCs containing 5-ASA powder exhibited a MRT of 7.0 +/- 1.0 h, these two types of preparations have suggested sustained release characteristics.

Stability of diclofenac sodium in the inclusion complex with beta-cyclodextrin in the solid state

The aim of this study was to characterize the thermal stability of diclofenac sodium both alone and in the inclusion complex with beta-cyclodextrin in the solid state, by determination of the number of the products of its decomposition, which were identified by GC-MS. The molar ratio of diclofenac sodium in the inclusion complex with beta-cyclodextrin was 1:1. The decomposition of diclofenac sodium both alone and in inclusion complex with beta-cyclodextrin occurred according to the first-order reaction. The HPLC of the samples thermostated at 80 degrees C gave five products of decomposition, which were identified by GC-MS. Diclofenac sodium in the inclusion complex with beta-cyclodextrin was more thermally stable. Thermal decomposition of diclofenac sodium leads to formation of five products, of which 4-chloro-10H-9-acridinone had not been reported previously in the literature.

Factors influencing the bioavailability of peroral formulations of drugs for dogs

The oral route is presently the preferred route of drug delivery. Poor oral bioavailability results in variable concentrations of drugs in the plasma and variable pharmacological responses, in addition to higher product costs. The unique canine physiology, anatomy and biochemistry makes designing canine dosage forms a challenging exercise. This article reviews the physicochemical, physiological, pharmacokinetic, pharmacological and formulation factors that can influence the drug availability of the oral formulations in dogs in an effort to provide a source of data to aid development of canine drug products with superior bioavailability.

In vivo performance of wax matrix granules prepared by a twin-screw compounding extruder

The in vivo performance of wax matrix granules (WMGs) prepared by a twin-screw compounding extruder was evaluated in fasted beagle dogs. In vitro dissolution behavior of the model drug, diclofenac sodium (DS), from WMGs was strongly influenced by pH in a dissolution medium due to its solubility (DS is soluble in pH 6.8 and insoluble in pH 1.2 and 4.0) and was independent of paddle rotation rate (50, 100, and 200 rpm) of the dissolution apparatus. Pharmacokinetics parameters such as mean residence time (MRT) showed a sustained action of WMGs in beagle dogs; however, the transit time of WMGs in the small intestine is found to control total drug absorption. Furthermore, the values of the area under the curve (AUC) of the plasma concentration-time curve and the maximum concentration Cmax significantly decreased with decreases in hydroxypropylcellulose (HPC) content in WMGs. Good correlation between one in vitro dissolution parameter (mean dissolution time, MDT) and two in vivo parameters (AUC12 and MRT) suggested that it would be possible to design WMGs with a desired in vivo performance by controlling HPC content.

Relationship between gelation rate of controlled-release acetaminophen tablets containing polyethylene oxide and colonic drug release in dogs

PURPOSE

We hypothesized that sufficient gelation of orally administered hydrophilic matrix tablets before they reach the colon could, as a result of continuous erosion of the gelated matrix, prevent the decrease in colonic drug release which normally occurs here. The purpose of this study was to elucidate the effect of gelation of hydrophilic matrices containing polyethylene oxide on colonic drug release in dogs using controlled-release (CR) acetaminophen tablets.

METHODS

Two types of CR tablets were prepared, a slow gelling tablet (SG) and a rapid gelling tablet (RG) containing an extra highly water soluble filler. In vitro and in vivo performance were examined.

RESULTS

SG and RG showed similar drug release behavior in vitro. In oral administration to dogs, the two formulations showed similar gastrointestinal transit, reaching the colon within 2-4 h after oral dosing. Further, they showed similar maximum plasma levels (Cmax) and time to Cmax (Tmax). In contrast, however, the two tablets produced different plasma levels from 2 h post-dosing, with plasma levels of RG higher than those of SG and with smaller individual variation. Directly observed colonic drug release behavior of RG was similar to in vitro drug release, whereas that from SG was suppressed.

CONCLUSIONS

Colonic drug release is closely related to the gelation of hydrophilic matrix, and rapid gelation provides continuous in vivo drug release.

Relationship between the phasic period of interdigestive migrating contraction and the systemic bioavailability of acetaminophen in dogs

The relationships of the phasic period of interdigestive migrating contraction to gastrointestinal (GI) transit of drugs and their oral absorption were investigated in mongrel dogs by simultaneous oral dosing of acetaminophen (AAP) and salicylazosulfapyridine (SASP) at the starting points of the phase I and phase III periods of gastric contractions. Strain-gauge force transducers were surgically sutured onto the serosa of the GI tracts in the dogs to measure the interdigestive migrating contractions. The mean absorption time of AAP and the time for the first appearance of sulfapyridine (a bacterial metabolite of SASP in the colon) in plasma were used as the indices of gastric emptying time (GET) and small intestinal transit time (SITT), respectively. In individual dogs, the GET and the SITT at phase I showed a clear delay in comparison with those at phase III. For AAP used as a marker compound here, the systemic bioavailability after oral dosing to intact beagle dogs at doses of 3, 10, and 20 mg/kg was about 55, 63, and 79%, suggesting that AAP undergoes a non-linear hepatic clearance. At a dose of AAP 20 mg/kg, the systemic bioavailability of AAP was 100% in the case of dosing at phase III, but was reduced by half when dosing at phase I. These results indicate that, in oral dosing, the transit of drugs through the GI tract was clearly affected by the phases of gastric contractions.(ABSTRACT TRUNCATED AT 250 WORDS)