Companion animal physiology and dosage form performance

Controlling the Solubility, Release Rate and Permeation of Riluzole with Cyclodextrins

Riluzole (RLZ), a sodium channel-blocking benzothiazole anticonvulsant BCS class II drug, is very slightly soluble in aqueous medium. To improve aqueous solubility and modulate dissolution rate and membrane permeability, complex formation of RLZ with two cyclodextrin, α-cyclodextrin (α-CD) and sulfobutylether-β-cyclodextrin (SBE-β-CD), was studied. The stability constants demonstrated a greater affinity of SBE-β-CD towards RLZ compared to α-CD. A solubility growth of 1.7-fold and 3.7-fold with α-CD and SBE-β-CD, respectively, was detected in the solutions of 1% cyclodextrins and accompanied by the permeability reduction. For 1% CD solutions, several biopolymers (1% w/v) were tested for the membrane permeability under static conditions. The synergistic positive effect of α-CD and polymer on the solubility accompanied by unchanged permeability was revealed in RLZ/α-CD/PG, RLZ/α-CD/PEG400, and RLZ/α-CD/PEG1000 systems. Solid RLZ/CD complexes were prepared. Dynamic dissolution/permeation experiments for the solid samples disclosed the characteristic features of the release processes and permeation rate through different artificial membranes. The maximal permeation rate was determined across the hydrophilic semi-permeable cellulose membrane followed by the lipophilic PermeaPad barrier (model of intestinal and buccal absorption) and polydimethylsiloxane-polycarbonate membrane (simulating transdermal delivery way). Different mode of the permeation between the membranes was estimated and discussed.

Development of a canine artificial colonic mucus model for drug diffusion studies

Colonic mucus is a key factor in the colonic environment because it may affect drug absorption. Due to the similarity of human and canine gastrointestinal physiology, dogs are an established preclinical species for the assessment of controlled release formulations. Here we report the development of an artificial colonic mucus model to mimic the native canine one. In vitro models of the canine colonic environment can provide insights for early stages of drug development and contribute to the implementation of the 3Rs (refinement, reduction, and replacement) of animal usage in the drug development process. Our artificial colonic mucus could predict diffusion trends observed in native mucus and was successfully implemented in microscopic and macroscopic assays to study macromolecular permeation through the mucus. The traditional Transwell set up was optimized with the addition of a nylon filter to ensure homogenous representation of the mucus barrier in vitro. In conclusion, the canine artificial colonic mucus can be used to study drug permeation across the mucus and its flexibility allows its use in various set ups depending on the nature of the compound under investigation and equipment availability.

Oral fluconazole has variable pharmacokinetics in dogs

The purpose of this study was to assess the effects of food and manufacturer on the oral bioavailability of fluconazole in dogs. We hypothesized feeding would decrease fluconazole bioavailability and large variability between manufacturers would occur. Six healthy purpose-bred dogs aged 2-3 years, weighing 9.5-13.7 kg, were enrolled. Each dog was administered a 100 mg fluconazole tablet from three FDA approved manufacturers (1-Glenmark, 2-Citron, 3-Harris) in a randomized crossover block study, fasted for 12 h (fasted) or 15 min after feeding (fed); each dog had 6 treatments. Blood was collected for 72 h after dosing with a 10-day washout between treatments. Fluconazole plasma concentrations were determined with mass spectrometry. Overall variability in dose-normalized drug exposure (AUC/dose) was large (range 1.9-2.9x) within each treatment, while the overall range across all treatments was 3.3-fold. The inter-dog variability in the terminal half-life was also large, 3.1-fold. The mean fed relative oral bioavailability was lower (82%-90%) compared to fasted for each formulation. Due to the large variability, the formulations were not bioequivalent. These data suggest the variability in the half-life was a major contributor to the large variability in fluconazole pharmacokinetics in dogs, while the feeding status and manufacturer were minor contributors.

Colonic drug delivery: Formulating the next generation of colon-targeted therapeutics

Colonic drug delivery can facilitate access to unique therapeutic targets and has the potential to enhance drug bioavailability whilst reducing off-target effects. Delivering drugs to the colon requires considered formulation development, as both oral and rectal dosage forms can encounter challenges if the colon's distinct physiological environment is not appreciated. As the therapeutic opportunities surrounding colonic drug delivery multiply, the success of novel pharmaceuticals lies in their design. This review provides a modern insight into the key parameters determining the effective design and development of colon-targeted medicines. Influential physiological features governing the release, dissolution, stability, and absorption of drugs in the colon are first discussed, followed by an overview of the most reliable colon-targeted formulation strategies. Finally, the most appropriate in vitro, in vivo, and in silico preclinical investigations are presented, with the goal of inspiring strategic development of new colon-targeted therapeutics.

Pharmacokinetics of isavuconazole in healthy cats after oral and intravenous administration

Background

Isavuconazole is a triazole antifungal drug that has shown good efficacy in human patients. Absorption and pharmacokinetics have not been evaluated in cats.

Objectives

To determine the pharmacokinetics of isavuconazole in cats given a single IV or PO dose.

Animals

Eight healthy, adult research cats.

Methods

Four cats received 100 mg capsules of isavuconazole PO. Four cats received 5 mg/kg isavuconazole solution IV. Serum was collected at predetermined intervals for analysis using ultra‐high performance liquid chromatography‐tandem mass spectrometry. Data were analyzed using a 2‐compartment uniform weighting pharmacokinetic analysis with lag time for PO administration and a 2 compartment, 1/y² weighting for IV administration. Predicted 24 and 48‐hour dosing intervals of 100 mg isavuconazole administered PO were modeled and in vitro plasma protein binding was assessed.

Results

Both PO and IV drug administration resulted in high serum concentrations. Intravenous and PO formulations of isavuconazole appear to be able to be used interchangeably. Peak serum isavuconazole concentrations occurred 5 ± 3.8 hours after PO administration with an elimination rate half‐life of 66.2 ± 55.3 hours. Intersubject variability was apparent in both the PO and IV groups. Two cats vomited 6 to 8 hours after PO administration. No adverse effects were observed in the IV group. Oral bioavailability was estimated to be approximately 88%. Serum protein binding was calculated to be approximately 99.0% ± 0.03%.

Conclusions and Clinical Importance

Isavuconazole might prove to be useful in cats with fungal disease given its favorable pharmacokinetics. Additional studies on safety, efficacy, and tolerability of long‐term isavuconazole use are needed.

Targeted oral peptide delivery using multi-unit particulates: Drug and permeation enhancer layering approach

Oral delivery of peptides is a challenge due to their instability and their limited transport and absorption characteristics within the gastrointestinal tract. In this work, we used layering techniques in a fluidized bed dryer to create a configuration in which the active peptide, permeation enhancers, and polymers are coated to control the release of the peptide. Formulations were developed to disintegrate at pH values of 5.5 and 7.0. In addition, sustained-release or mucoadhesive polymers were coated to trigger release at a desired site in the gastrointestinal tract. Dissolution studies with a USP Type I (basket) apparatus confirmed the duration of release. Pharmacokinetic studies were performed in beagle dogs to evaluate bioavailability. A high-disintegration pH was found to be advantageous in enhancing bioavailability.

An overview of in vitro, ex vivo and in vivo models for studying the transport of drugs across intestinal barriers

Oral administration is the most commonly used route for drug delivery owing to its cost-effectiveness, ease of administration, and high patient compliance. However, the absorption of orally delivered compounds is a complex process that greatly depends on the interplay between the characteristics of the drug/formulation and the gastrointestinal tract. In this contribution, we review the different preclinical models (in vitro, ex vivo and in vivo) from their development to application for studying the transport of drugs across intestinal barriers. This review also discusses the advantages and disadvantages of each model. Furthermore, the authors have reviewed the selection and validation of these models and how the limitations of the models can be addressed in future investigations. The correlation and predictability of the intestinal transport data from the preclinical models and human data are also explored. With the increasing popularity and prevalence of orally delivered drugs/formulations, sophisticated preclinical models with higher predictive capacity for absorption of oral formulations used in clinical studies will be needed.

Pharmacokinetic analysis of two different doses of simvastatin following oral administration in dogs

Simvastatin, used orally to treat hyperlipidemia, exhibits highly variable pharmacokinetics (PKs) in humans. The aim of this study was to investigate simvastatin PKs using noncompartmental analysis and population PK models following a single oral administration of two doses (20 and 80 mg) in dogs. Forty beagle dogs were randomly divided into two groups corresponding to the two doses. Blood samples were collected from each group according to the assigned schedule after oral administration. The plasma concentration of simvastatin was determined using liquid chromatography-tandem mass spectrometry. The area under the curve and maximum concentration of simvastatin increased in a dose-dependent manner with high variability. A two-compartment model with first-order absorption (K_a  = 1.83 hr^-1 ) and first-order elimination (clearance [CL/F] = 292 L/h; volume of distribution in the central compartment [V_c /F] = 1506 L) well described the PKs of simvastatin in dogs. Large variability in the PKs of simvastatin was quantitated via modeling approaches, allowing the differentiation of between-subject variability (144.8 CV% for K_a ; 94.7 CV% for CL/F; 97.5 CV% for V_c /F) and residual variability (62.7%). These findings will help facilitate the development of an optimal dose regimen of simvastatin in canines with hypercholesterolemia and may be useful in developing novel formulations.

Feline comorbidities: What do we really know about feline triaditis?

PRACTICAL RELEVANCE

Feline triaditis describes concurrent pancreatitis, cholangitis and inflammatory bowel disease (IBD). The reported prevalence is 17-39% in ill referral patients. While the aetiology is poorly understood, it is known to include infectious, autoimmune and physical components. What is not known is whether different organs are affected by different diseases, or the same process; indeed, triaditis may be part of a multiorgan inflammatory disease. Feline gastrointestinal tract anatomy plays its role too. Specifically, the short small intestine, high bacterial load and anatomic feature whereby the pancreatic duct joins the common bile duct before entering the duodenal papilla all increase the risk of bacterial reflux and parenchymal inflammation. Inflammation may also be a sequela of bowel bacterial translocation and systemic bacteraemia.

DIAGNOSTIC CHALLENGES

Cholangitis, pancreatitis and IBD manifest with overlapping, vague and non-specific clinical signs. Cholangitis may be accompanied by increased serum liver enzymes, total bilirubin and bile acid concentrations, and variable ultrasonographic changes. A presumptive diagnosis of pancreatitis is based on increased serum pancreatic lipase immunoreactivity or feline pancreas-specific lipase, and/or abnormal pancreatic changes on ultrasonography, though these tests have low sensitivity. Diagnosis of IBD is challenging without histopathology; ultrasound findings vary from normal to mucosal thickening or loss of layering. Triaditis may cause decreased serum folate or cobalamin (B12) concentrations due to intestinal disease and/or pancreatitis. Triaditis can only be confirmed with histopathology; hence, it remains a presumptive diagnosis in most cases.

EVIDENCE BASE

The literature on feline triaditis, pancreatitis, cholangitis and IBD is reviewed, focusing on histopathology, clinical significance and diagnostic challenges. Current management recommendations are provided. Further studies are needed to understand the complex pathophysiology, and in turn improve diagnosis and treatment.

Development of a Novel Controlled-Release Tablet of Pregabalin: Formulation Variation and Pharmacokinetics in Dogs and Humans

Background

Novel three-layered (TL) tablet systems were compared with both monolithic matrix (MM) formulations and a commercial immediate-release (IR) capsule to develop once-a-day (OAD) pregabalin tablets.

Methods

The physical properties of the TL tablets, including dissolution and swelling rates, were compared with those of the MM tablets and the pharmacokinetic parameters of the TL tablet were compared with those of an IR capsule in beagles and humans.

Results

Our results indicated that the same amount of a hydrophilic polymer in the formulations had similar dissolution profiles at 12 h, regardless of the tablet geometry. However, the degree of tablet swelling differed, with larger amounts of polymer in the tablets showing a greater degree of swelling. In addition, TL tablets swelled more rapidly compared with MM tablets. For the pharmacokinetic study of the TL tablet, the beagles demonstrated absorption results similar to those of an IR capsule, whereas the humans demonstrated low total absorption compared with an IR capsule. The time of the peak plasma concentration at 6 h in the fed state of humans coincided with the results of the study on beagles.

Conclusion

The novel TL tablet system of pregabalin may prove to be helpful in developing improved formulations with better continuous drug absorption for OAD administration.

In vivo evaluation of targeted delivery of biological agents using barium sulfate

This study was aimed to monitor the transit through the intestine by X-ray imaging using barium sulfate (BS) as tracer. The in vitro features of monolithic tablets were correlated with their in vivo behavior in order to provide a tool for the development of targeted formulations containing macromolecular bioactive agents. The impact of BS on various matrices (neutral, ionic) was studied in simulated fluids using the disintegration time (DT) as main parameter. Dry tablets were characterized by spectroscopic methods (X-ray diffraction and Infra-Red) and scanning electron microscopy (SEM). The selected formulations were followed in a beagle dog model. The in vivo and in vitro DT of tablets formulated with BS were compared. Results: anionic excipients carboxymethylcellulose (CMC) and carboxymethylstarch (CMS) protected the active ingredient from the gastric acidity, ensuring its targeted delivery in the intestine. The SEM analysis, before and after transit in simulated fluids, showed that BS remained in the tablets allowing their good follow-up in vivo. The incorporation of 30% protein in tablets with 40% BS had no impact on their behavior. In conclusion, BS and X-ray imagery could be a good alternative to scintigraphy for development of targeted formulations containing high molecular weight bioactive agents.

Simultaneous Evaluation of Dissolution and Permeation of Oral Drug Solid Formulations for Predicting Absorption Rate-Limiting Factors and In Vitro-In Vivo Correlations: Case Study Using a Poorly Soluble Weakly Basic Drug

Combined dissolution and permeation systems are designed to simultaneously assess the dissolution of a pharmaceutical dosage form and the permeation of dissolved drugs therefrom. However, there were still some limitations on predicting the possible absorption rate-limiting steps and improving the in vitro-in vivo correlation (IVIVC) of a complete dosage form. In this study, the modified biorelevant media with some solubilizers and pH modifiers were integrated into the drug dissolution/absorption simulating system (DDASS). Indapamide, a poorly soluble compound (pKa = 8.8), was selected to validate the applicability of the modified biorelevant media. The elution and permeation dynamics of indapamide were investigated by using appropriate solubilizing agents in the DDASS. The absorption behaviors were analyzed after oral administration of indapamide in beagle dogs. The absorption rate-limiting steps and IVIVCs were predicted from the dissolution-permeation-absorption dynamic parameters. As a result, the absorption fraction of indapamide in the FaSSIF_mod of DDASS was estimated to be approximately 100%, in accordance with its high permeability. The ratios of permeation rate to elution rate were 2.55 and 3.34 for the immediate- and sustained-release tablets of indapamide, respectively, suggesting a dissolution rate-limiting absorption for indapamine. In addition, point-to-point correlations were established between in vitro elution and in vivo absorption by the nonlinear and linear regression analysis ways (r > 0.85). The findings indicate that DDASS is a promising technique to develop improved IVIVCs of a complete dosage form, and the FaSSIF_mod is suitable to predict the possible absorption rate-limiting steps of poorly soluble drugs in DDASS.

The pharmacokinetics of gabapentin in cats

BACKGROUND

Gabapentin is the most commonly prescribed medication for the treatment of chronic musculoskeletal pain in cats. Despite this common and chronic usage, clinically relevant pharmacokinetic data is lacking.

OBJECTIVES

To evaluate the pharmacokinetics of clinically relevant dosing regimens of gabapentin in cats.

ANIMALS

Eight research-purpose mixed-breed cats.

METHODS

Cats were enrolled in a serial order, non-randomized pharmacokinetic study. Gabapentin was administered as an IV bolus (5 mg/kg), orally (10 mg/kg) as a single dose or twice daily for 2 weeks, or as a transdermal gel (10 mg/kg) in serial order. Serial blood samples were collected up to 48 hours. Plasma concentrations were determined using Ultra Performance Liquid Chromatography-Mass Spectrometry. Compartmental analysis was used to generate gabapentin time-concentration models.

RESULTS

After IV administration CL (median (range)) and terminal half-life were 160.67 mL/kg*hr (119.63-199.11) and 3.78 hours (3.12-4.47), respectively. The oral terminal half-life was 3.63 hours (2.96-4.77), and 3.72 hours (3.12-4.51) for single and repeated dosing. T_MAX and C_MAX , as predicted by the model were 1.05 hours (0.74-2.11), and 12.42 μg/mL (8.31-18.35) after single oral dosing, and 0.77 hours (0.58-1.64), and 14.78 μg/mL (9.70-18.41) after repeated oral dosing. Bioavailability after a single oral dose was 94.77% (82.46-122.83).

IMPORTANCE

Repeated oral dosing of gabapentin did not alter the drug's pharmacokinetics, making dose adjustments unnecessary with long-term treatment. As prepared, the transdermal route is an inappropriate choice for drug administration. These relevant data are important for future studies evaluating potential efficacy of the medication for treating chronic pain states in cats.

Roux-en-Y duodenojejunostomy improves gastric emptying in experimental obstruction of the distal duodenum

Introduction

We undertook a comparative survey of gastric emptying (GE) kinetics after two variants of bypass surgery for upper bowel obstruction.

Material & methods

In 10 dogs with experimental upper bowel obstruction, five were randomized to obtain gastrojejunal anastomosis (GA), and the other five received Roux-en-Y duodenojejunal anastomosis (DA). Duplicate scintigraphic measurements of GE of a solid meal were accomplished in every animal before surgery and during the early (2–3 weeks), medium (3 months), and late (6 months) post-operative period. The GE curves were fitted with a power-exponential function to derive the GE half time T½, and the curve shape parameter S.

Results

Early after surgery T½ slightly decreased by -18±21 min in the DA group and lengthened by 91±37 min in the GA group (p = 0.042). In both groups an increase in the S parameter was found then. In either group T½ gradually declined towards the basal value during the medium and late post-operative period. On the other hand, net differences relative to the basal situation in the S values appeared to be positive in the GA group (0.32±0.11 at 3 months; 0.64±0.19 at six months), and negative in the DA group (-0.30±0.09 at 3 months; -0.01±0.20 at six months). Hence a statistically significant contrast was found between those differences: p = 0.0022 at 3 months, and p = 0.045 at six months after the surgery.

Conclusion

Roux-en-Y duodenojejunal anastomosis appears to be superior to the classical gastrojejunal anastomosis while restoring patency of the gastrointestinal passage in the case of upper bowel obstruction.

The effect of reducing energy density, via the addition of water to dry diet, on body weight and activity in dogs

Approximately 40 % of pet dogs are estimated to be overweight and this is associated with health conditions significantly reducing life span and quality. In cats, dietary energy dilution has been reported to increase activity levels and aid healthy body-weight maintenance. Our aim was to investigate this in dogs. For 28 d, a complete and balanced standard dry diet, hydrated to a total moisture content (TMC) of 72 %, was offered to forty-six dogs at individual maintenance energy requirements (MER). Intake, body weight and activity were measured. For the following 28 d, the dry diet was offered at 200 % of MER with or without hydration (7·6 or 72 % TMC) and measurements repeated. When offered diets in excess, body weight increased significantly faster (19·3 g/d) with the hydrated diet (P = 0·001), but activity levels did not change from baseline (P = 0·392), while activity reduced significantly with the dry diet (about 15 %; P < 0·001). Dogs completely compensated for the reduction of dietary energy content, indicating that this is not a useful strategy for maintaining body weight when offered excess food.

Biopharmaceutical Evaluation and CMC Aspects of Oral Modified Release Formulations

This article discusses the range of outcomes from biopharmaceutical studies of specific modified release (MR) product examples in preclinical models and humans. It touches upon five major biopharmaceutical areas for MR drug products: (1) evidence for regional permeability throughout the GI tract, (2) susceptibility to food-effect, (3) susceptibility to pH-effect, (4) impact of chronopharmacology in designing MR products, and (5) implications to narrow therapeutic index products. Robust bioperformance requires that product quality is met through a thorough understanding of the appropriate critical quality attributes that ensure reliable and robust manufacture of a MR dosage form. The quality-by-design (QbD) aspects of MR dosage form design and development are discussed with the emphasis on the regulatory view of the data required to support dosage form development.

Exploring Canine-Human Differences in Product Performance. Part II: Use of Modeling and Simulation to Explore the Impact of Formulation on Ciprofloxacin In Vivo Absorption and Dissolution in Dogs

This study explored the in vivo performance of three oral ciprofloxacin formulations (oral solution, fast, or slow dissolving tablets) in beagle dogs. The in vivo absorption and dissolution behaviors, estimated with in silico mechanistic models, were compared to the results previously published in human volunteers. Six normal healthy male beagle dogs (five to completion) received three oral formulations and an intravenous infusion in a randomized crossover design. Plasma ciprofloxacin concentrations were estimated by tandem mass spectrometry detection. A mechanistic absorption model was used to predict the in vivo dissolution and absorption characteristics of the oral formulations. Canine ciprofloxacin absorption was constrained to the duodenum/jejunum. This absorption window was far narrower than that seen in humans. Furthermore, while substantial within-individual variability in drug absorption was seen in human subjects, a greater magnitude of variability was observed in dogs. For three sets of data, a lag time in gastric emptying was necessary to improve the accuracy of model-generated in vivo blood level profile predictions. In addition to species-associated dissimilarities in drug solubilization due to human versus canine differences in gastrointestinal fluid compositions, the far more rapid intestinal transit time and potential segmental differences in drug absorption needed to be considered during human-canine extrapolation of oral drug and drug product performance. Through the use of mechanistic models, the data generated in the human and canine studies contributed insights into some aspects of the interspecies differences to be considered when extrapolating oral bioavailability/formulation effect data between dogs and humans.

Considerations for the development of in vitro dissolution tests to reduce or replace preclinical oral absorption studies

The pharmaceutical development of new chemical entities can be hampered by their solubility and/or dissolution limitations. Currently, these properties are characterised mostly during in vivo pre-clinical studies. The development of appropriate in vitro methods to study the solubility and dissolution properties in preclinical species would lead to a significant reduction or replacement of the animal experiments at this stage of development. During clinical development, media simulating the human gastrointestinal tract fluids are commonly used and a similar approach mimicking laboratory animals' gastrointestinal tract fluids would impact on the preclinical stage of development. This review summarises the current knowledge regarding the gastrointestinal physiology of the most common laboratory animals, and animal simulated gastric and intestinal media are proposed.

Key Considerations in Designing Oral Drug Delivery Systems for Dogs

The present review discusses the pharmaceutical impact of the anatomy and physiology of the canine gastrointestinal tract to provide a comprehensive guide to the theories and challenges associated with the development of oral drug delivery systems for dogs. Novel pharmaceutical technologies applied to veterinary drugs are discussed indicating the advantages and benefits for animals. There are currently immense research and development efforts being funneled into novel canine health products. Such products are being used to overcome limitations of drugs that display site-dependent absorption or possess poor biopharmaceutical properties. Techniques that are employed to increase bioavailability of the Biopharmaceutics Classification System class II drugs are discussed in this article. Furthermore, an overview of palatable oral formulations for dog care is provided as an approach to easy administration. In vitro and in vivo evaluation and correlation of oral drug formulations in dogs are also addressed. This article assesses the outlook of canine oral drug development recognizing substantial growth forecasts of the dog care market.

A Food Effect Study of an Oral Thrombin Inhibitor and Prodrug Approach To Mitigate It

LB30870, a new direct thrombin inhibitor, showed 80% reduction in oral bioavailability in fed state. The present study aims to propose trypsin binding as a mechanism for such negative food effect and demonstrate a prodrug approach to mitigate food effect. Effect of food composition on fed state oral bioavailability of LB30870 was studied in dogs. Various prodrugs were synthesized, and their solubility, permeability, and trypsin binding affinity were measured. LB30870 and prodrugs were subject to cocrystallization with trypsin, and the X-ray structures of cocrystals were determined. Food effect was studied in dogs for selected prodrugs. Protein or lipid meal appeared to affect oral bioavailability of LB30870 in dogs more than carbohydrate meal. Blocking both carboxyl and amidine groups of LB30870 resulted in trypsin Ki values orders of magnitude higher than that of LB30870. Prodrugs belonged to either Biopharmaceutical Classification System I, II, or III. X-ray crystallography revealed that prodrugs did not bind to trypsin, but instead their hydrolysis product at the amidine blocking group formed cocrystal with trypsin. A prodrug with significantly less food effect than LB30870 was identified. Binding of prodrugs to food components such as dietary fiber appeared to counteract the positive effect brought with the prodrug approach. Further formulation research is warranted to enhance the oral bioavailability of prodrugs. In conclusion, this study is the first to demonstrate that the negative food effect of LB30870 can be attributed to trypsin binding. Trypsin binding study is proposed as a screening tool during lead optimization to minimize food effect.

Disposition of Extended Release Levetiracetam in Normal Healthy Dogs After Single Oral Dosing

Background

Levetiracetam is an anticonvulsant used for control of canine epilepsy. An extended release preparation should improve dosing convenience.

Objectives

To determine the disposition of extended release levetiracetam in normal dogs after single dosing.

Animals

Pharmacokinetic study: 16 healthy, adult dogs.

Methods

Using a partially randomized crossover study, levetiracetam (30 mg/kg) was administered intravenously (IV) and orally (PO) as extended release preparation with or without food. Blood was collected for 24 hours (IV) or 36 hours (PO). Serum levetiracetam was quantitated by immunoassay and data were subjected to noncompartmental analysis.

Results

Pharmacokinetic parameters for fasted versus fed animals, respectively, were (mean ± SEM): C_max = 26.6 ± 2.38 and 30.7 ± 2.88 μ/mL, T_max = 204.3 ± 18.9 and 393.8 ± 36.6 minutes, t_1/2 = 4.95 ± 0.55 and 4.48 ± 0.48 hours, MRT = 9.8 ± 0.72 and 10 ± 0.64 hours, MAT = 4.7 ± 0.38 and 5.6 ± 0.67 hours, and F = 1.04 ± 0.04 and 1.26 ± 0.07%. Significant differences were limited to T_max (longer) and F (greater) in fed compared to fasted animals. Serum levetiracetam concentration remained above 5 μ/mL for approximately 20 hours in both fasted and fed animals.

Conclusions and Clinical Importance

Extended release levetiracetam (30 mg/kg q12h), with or without food, should maintain concentrations above the recommended minimum human therapeutic concentration.

Food Effect in Humans: Predicting the Risk Through In Vitro Dissolution and In Vivo Pharmacokinetic Models

In vitro and in vivo experimental models are frequently used to assess a new chemical entity's (NCE) biopharmaceutical performance risk for food effect (FE) in humans. Their ability to predict human FE hinges on replicating key features of clinical FE studies and building an in vitro-in vivo relationship (IVIVR). In this study, 22 compounds that span a wide range of physicochemical properties, Biopharmaceutics Classification System (BCS) classes, and food sensitivity were evaluated for biorelevant dissolution in fasted- and fed-state intestinal media and the dog fed/fasted-state pharmacokinetic model. Using the area under the curve (AUC) as a performance measure, the ratio of the fed-to-fasted AUC (FE ratio) was used to correlate each experimental model to FE ratio in humans. A linear correlation was observed for the in vitro dissolution-human IVIVR (R (2) = 0.66, % mean square error 20.7%). Similarly, the dog FE ratio correlated linearly with the FE ratio in humans (R (2) = 0.74, % mean square error 16.25%) for 15 compounds. Data points near the correlation line indicate dissolution-driven mechanism for food effect, while deviations from the correlation line shed light on unique mechanisms that can come into play such as GI physiology or unusual physicochemical properties. In summary, fed/fasted dissolution studies and dog PK studies show a reasonable correlation to human FE, hence are useful tools to flag high-risk NCEs entering clinical development. Combining kinetic dissolution, dog FE model and in silico modeling one can study FE mechanism and formulation strategies to mitigate the FE risk.

Application and validation of an advanced gastrointestinal in vitro model for the evaluation of drug product performance in pharmaceutical development

Methods to understand and predict the oral bioavailability of drug products are a prioritized research area within the pharmaceutical industry. Models to predict oral bioavailability have the potential to reduce risk, time, and cost in development as well as decrease the need for animal studies. The TNO intestinal model (TIM-1) is an advanced dissolution model deployed by AstraZeneca since 2008. This article presents a systematic evaluation of TIM-1 against in vivo data. The relative performance of compounds and formulations tested in TIM-1 and in vivo was compared both by a qualitative analysis and a linear regression analysis of relative exposure measures between test and reference formulations in TIM-1 and in vivo. The TIM-1 correctly predicted in vivo rank order in 84% and 79% of cases for AUC and Cmax , respectively, when using the 3-h time point. There was only one case for Cmax in which TIM-1 did not predict an in vivo difference. The correlation coefficient (R(2) ) between relative (test vs. reference formulations) fraction available in TIM-1 after 3 h and AUC was 0.78. Thus, this study suggests that the TIM-1 system can be used to assess the risk for significant differences in exposure between formulations and compound modifications.

Size discrimination in rat and mouse gastric emptying

OBJECTIVES

To investigate the relationship between particle size and gastric emptying in rodents using radiolabeled insoluble polymethyl methacrylate (PMMA) microcapsules/beads.

METHODS

PMMA microcapsules (50-500 µm) and beads (0.5-3 mm) loaded with technetium-99 m diethylenetriamine pentaacetic acid ((99m) Tc-DTPA) were administered to ICR mice or Sprague Dawley (SD) rats by oral gavage. Gamma scintiscans were acquired initially following administration and then at hourly intervals to 4 hours.

RESULTS

Scintiscans revealed that the smallest PMMA microcapsules (50-100 µm) or beads (0.5-1 mm) were impeded in the stomach and emptied slower than large particles in both rodent species. In mice, no significant difference in gastric emptying was found with microcapsules between 100 and 300 µm in diameter (p = 0.25) and particles more than 300 µm could not be administered. In rats, capsules containing 0.5-3 mm beads were stuck to the esophagus (up to 1 hour), this was a limitation of dosing beads of this size because they cannot be suspended in a liquid media for oral gavage purposes. Beads with diameters of 2-3 mm stayed in the stomach for up to 4 hours.

CONCLUSIONS

The cut-off emptying size in ICR mice could not be determined, due to the limitation of current available dosing methods. The cut-off emptying size in SD rats was between 1.5 and 2 mm. Therefore, particles with a diameter greater than 2 mm should not be used for gastric emptying studies of intact particles in SD rats, as their emptying is retarded in the stomach.

Preformulation evaluation of AZD1305, an oxabispidine intended for oral and intravenous treatment

AIM

AZD1305 is a novel, water-soluble investigational antiarrhythmic agent for restoration and maintenance of sinus rhythm in atrial fibrillation patients. The present studies were performed to evaluate the possibility for further development of the compound.

METHODS

A set of technical approaches were used, including X-ray powder diffractometry, differential scanning calorimetry, thermogravimetrical analysis, dynamic vapor sorption, scanning electron microscopy, salt screen, and liquid chromatography.

RESULTS

AZD1305 is a crystalline oxabispidine and its neutral form is a base with a pK(a) of 9.9. The substance degrades with higher temperature and lower pH. The free base of the solid substance is stable at 25°C (closed container), 40°C/75% relative humidity (open container), and at 50°C (closed container) for at least 3 months. The free base of AZD1305 is polymorphic with two known forms. Both forms are non-hygroscopic ansolvates with melting points of approximately 90°C. No salt was found with overall improved properties. The substance had a strong odor, which was reduced by increased particle size.

CONCLUSIONS

The free base of AZD1305 seemed to be the most suitable agent for product development even though it has a fairly low melting point and occurred as two different crystal forms. Form B was the most stable thermodynamically in the temperature interval of interest.

Species comparison of oral bioavailability, first-pass metabolism and pharmacokinetics of acetaminophen

Species differences in oral bioavailability, first-pass metabolism and pharmacokinetics of biopharmaceutics classification system (BCS) class I compound acetaminophen were studied. The absolute bioavailability was 42.2%, 39.0%, 44.5%, 75.5% and 91.0% in chickens, turkeys, dogs, pigs and horses, respectively. After hydrolysis of metabolites by beta-glucuronidase/sulfatase, apparent bioavailability increased significantly in all species (turkeys: 72.4%, dogs: 100.5%, pigs: 102.2%), except horses (91.6%). Mean metabolic ratios of [acetaminophen glucuronide]/[acetaminophen] between 0 and 1h were significantly higher after oral dosing in turkeys, dogs and pigs, revealing the role of first-pass metabolism in incomplete bioavailability. Evidence of species differences in acetaminophen metabolism is provided by differences in plasma clearance, which was inversely proportional to bioavailability. In conclusion, differences in BA appeared to originate predominantly from differences in first-pass metabolism, demonstrating that the BCS high permeability classification of acetaminophen is consistent across the mammalian species studied. In turkeys, however, incomplete absorption additionally seemed to contribute to the low BA.

Influence of administration route on the biotransformation of amoxicillin in the pig

A comparison was made in the plasma concentration of the major metabolites of amoxicillin (AMO), i.e. amoxicilloic acid (AMA) and amoxicillin diketopiperazine-2',5'-dione (DIKETO) in portal and jugular venous plasma after oral (p.o.) and intravenous (i.v.) AMO administration to pigs, in order to study a possible presystemic degradation of AMO in the gastro-intestinal tract and liver. Almost identical plasma concentration-time curves were obtained for AMO and its metabolites in portal and jugular venous plasma, both after p.o. and i.v. AMO administration. Almost immediately after i.v. AMO administration, high AMA and DIKETO concentrations were measured in plasma, while after p.o. dosing, the metabolites appeared in plasma after almost complete absorption of AMO. No significant differences in pharmacokinetic parameters of AMO, AMA and DIKETO, derived from the concentration-time profiles in portal and jugular venous plasma were calculated, both after i.v. and p.o. AMO administration (P > 0.05). After p.o. administration, the half-life of elimination (t(1/2(el))) for AMA is at least two or three times the t(1/2(el)) of AMO (0.75 h for AMO vs. 2.69 h for AMA), indicating the slower clearance of the metabolite. It could be hypothesized that AMA is only eliminated by glomerular filtration, as its open beta-lactam structure might not be recognized by the transport carrier in the proximal tubule of the kidney. The results of the study indicate that AMO is not substantially metabolized presystemically in the gut and liver. Therefore, it may be assumed that the kidney may be the major organ for AMO biotransformation. Future in vivo and in vitro experiments should be performed to state this hypothesis.

Species differences in pharmacokinetics and pharmacodynamics

Veterinary medicine faces the unique challenge of having to treat many types of domestic animal species, including mammals, birds, and fishes. Moreover, these species have evolved into genetically unique breeds having certain distinguishable characteristics developed by artificial selection. The main challenge for veterinarians is not to select a drug but to determine, for the selected agent, a rational dosing regimen because the dosage regimen for a drug in a given species may depend on its anatomy, biochemistry, physiology, and behaviour as well as on the nature and causes of the condition requiring treatment. Both between- and within-species differences in drug response can be explained either by variations in drug pharmacokinetics (PK) or drug pharmacodynamics (PD), the magnitude of which varies from drug to drug. This chapter highlights selected aspects of species differences in PK and PD and considers underlying physiological and patho-physiological mechanisms in the main domestic species. Particular attention was paid to aspects of animal behaviour (food behaviour, social behavior, etc.) as a determinant of interspecies differences in PK or/and PD. Modalities of drug administration are many and result not only from anatomical, physiological and/or behavioural differences across species but also from management options. The latter is the case for collective/group treatment of food-producing animals, frequently dosed by the oral route at a herd or flock level. After drug administration, the main causes of observed inter-species differences arise from species differences in the handling of drugs (absorption, distribution, metabolism, and elimination). Such differences are most common and of greatest magnitude when functions which are phylogenetically divergent between species, such as digestive functions (ruminant vs. non-ruminant, carnivore vs. herbivore, etc.), are involved in drug absorption. Interspecies differences also exist in drug action but these are generally more limited, except when a particular targeted function has evolved, as is the case for reproductive physiology (mammals vs. birds vs. fishes; annual vs. seasonal reproductive cycle in mammals; etc.). In contrast, for antimicrobial and antiparasitic drugs, interspecies differences are more limited and rather reflect those of the pathogens than of the host. Interspecies difference in drug metabolism is a major factor accounting for species differences in PK and also in PD (production or not of active metabolites). Recent and future advances in molecular biology and pharmacogenetics will enable a more comprehensive view of interspecies differences and also between breeds with existing polymorphism. Finally, the main message of this review is that differences between species are not only numerous but also often unpredictable so that no generalisations are possible, even though for several drugs allometric approaches do allow some valuable interspecies extrapolations. Instead, each drug must be investigated on a species-by-species basis to guarantee its effective and safe use, thus ensuring the well-being of animals and safeguarding of the environment and human consumption of animal products.

Drug delivery systems in domestic animal species

Delivery of biologically active agents to animals is often perceived to be the poor relation of human drug delivery. Yet this field has a long and successful history of species-specific device and formulation development, ranging from simple approaches and devices used in production animals to more sophisticated formulations and approaches for a wide range of species. While several technologies using biodegradable polymers have been successfully marketed in a range of veterinary and human products, the transfer of delivery technologies has not been similarly applied across species. This may be due to a combination of specific technical requirements for use of devices in different species, inter-species pharmacokinetic, pharmacodynamic and physiological differences, and distinct market drivers for drug classes used in companion and food-producing animals. This chapter reviews selected commercialised and research-based parenteral and non-parenteral veterinary drug delivery technologies in selected domestic species. Emphasis is also placed on the impact of endogenous drug transporters on drug distribution characteristics in different species. In vitro models used to investigate carrier-dependent transport are reviewed. Species-specific expression of transporters in several tissues can account for inter-animal or inter-species pharmacokinetic variability, lack of predictability of drug efficacy, and potential drug-drug interactions.

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.