Controlled release of oxytetracycline in sheep

Prediction of subcutaneous drug absorption - Development of novel simulated interstitial fluid media for predictive subcutaneous in vitro assays

Media that mimic physiological fluids at the site of administration have proven to be valuable in vitro tools for predicting in vivo drug release, particularly for routes of administration where animal studies cannot accurately predict human performance. The objective of the present study was to develop simulated interstitial fluids (SISFs) that mimic the major components and physicochemical properties of subcutaneous interstitial fluids (ISFs) from preclinical species and humans, but that can be easily prepared in the laboratory and used in in vitro experiments to estimate in vivo drug release and absorption of subcutaneously administered formulations. Based on data from a previous characterization study of ISFs from different species, two media were developed: a simulated mouse-rat ISF and a simulated human-monkey ISF. The novel SISFs were used in initial in vitro diffusion studies with a commercial injectable preparation of liraglutide. Although the in vitro model used for this purpose still requires significant refinement, these two new media will undoubtedly contribute to a better understanding of the in vivo performance of subcutaneous injectables in different species and will help to reduce the number of unnecessary in vivo experiments in preclinical species by implementation in predictive in vitro models.

Prediction of subcutaneous drug absorption - do we have reliable data to design a simulated interstitial fluid?

For many years subcutaneous (SC) administration has represented the main route for delivering biopharmaceuticals. However, little information exists about the milieu in the subcutaneous tissue, especially about the properties/composition of the fluid present in this tissue, the interstitial fluid (ISF), which is one of the key elements for the drug release and absorption. Better knowledge on SC ISF composition, properties and dynamics may provide better insight into in vivo drug performance. In addition, a simulated SC ISF, which allows better prediction of in vivo absorption of drugs after subcutaneous administration based on in vitro release experiments, would help to improve formulation design, and reduce the number of animal studies and clinical trials required to obtain marketing authorization. To date, a universal medium for predicting drug solubility/release in the interstitial space does not exist. This review provides an overview of the currently available information on composition and physicochemical properties of SC ISF and critically discusses different isolation techniques in the context of information that could be gained from the isolated fluid. Moreover, it surveys current in vitro release media aiming to mimic SC ISF composition and highlights information gaps that need to be filled for designing a meaningful artificial SC ISF.

Pharmacokinetics of a Long-Acting Formulation of Oxytetracycline in Freshwater Crocodiles (Crocodylus siamensis) after Intramuscular Administration at Three Different Dosages

Simple Summary

The oxytetracycline long-acting formulation (OTC-LA) is used to treat sensitive pathogenic bacteria in the freshwater crocodile, Crocodylus siamensis. The pharmacokinetic profiles of differential dosages of OTC after intramuscular administration were investigated to determine the appropriate dosage for the treatment of bacterial infections in freshwater crocodiles. In freshwater crocodiles, dosages of 10 and 20 mg/kg produced OTC plasma concentrations higher than 2.0 µg/mL as a minimum inhibitory concentration (MIC) for 192 h and 216 h after intramuscular administration, respectively, while the OTC plasma concentration remained below the MIC of 2.0 µg/mL at a dosage of 5 mg/kg body weight (b.w.). When considering plasma protein binding of 32%, an intramuscular (i.m.) administration at a dosage of 10 mg/kg b.w. might be effective for two weeks to treat sensitive pathogenic bacteria in freshwater crocodiles.

Abstract

To date, the necessary pharmacokinetic information has been limited to establish suitable therapeutic plans for freshwater crocodiles. Therefore, this study was conducted to evaluate the pharmacokinetic profile of the oxytetracycline long-acting formulation (OTC-LA) in the freshwater crocodile, Crocodylus siamensis, following a single intramuscular (i.m.) administration at three different dosages of 5, 10 and 20 mg/kg body weight (b.w.). Blood samples were collected at assigned times up to 216 h after i.m. administration at the three different dosages. The plasma concentrations of OTC were measured using a validated liquid chromatography tandem-mass spectrometry (LC-MS/MS) method. The C_max (± SD) values of OTC were 2.15 ± 0.51 µg/mL, 7.68 ± 1.08 µg/mL and 17.08 ± 2.09 µg/mL at doses of 5, 10 and 20 mg/kg b.w., respectively. The elimination half-life values were 33.59 ± 2.51 h, 38.42 ± 5.47 h and 38.04 ± 1.98 h at dosages of 5, 10 and 20 mg/kg b.w., respectively. Based on the pharmacokinetic data, the pharmacokinetic/pharmacodynamic (PK/PD) index, the susceptibility break-point and plasma protein binding, a dosage once every two weeks of 10 mg/kg b.w. OTC intramuscularly might be suitable for initiating the treatment of susceptible bacterial infections in freshwater crocodiles. However, further PK/PD studies are warranted to confirm whether the dose rates used in this study can produce longer-term antimicrobial success for diseases caused by susceptible bacteria in freshwater crocodiles.

Disposition of a long-acting oxytetracycline formulation in Thai swamp buffaloes (Bubalus bubalis)

The present study aimed to characterize the pharmacokinetic profile of oxytetracycline long-acting formulation (OTC-LA) in Thai swamp buffaloes, Bubalus bubalis, following single intramuscular administration at two dosages of 20 and 30 mg/kg body weight (b.w.). Blood samples were collected at assigned times up to 504 h. The plasma concentrations of OTC were measured by high-performance liquid chromatography (HPLC). The concentrations of OTC in the plasma were determined up to 264 h and 432 h after i.m. administration at doses of 20 and 30 mg/kg b.w., respectively. The C_max values of OTC were 12.11 ± 1.87 μg/mL and 12.27 ± 1.92 μg/mL at doses of 20 and 30 mg/kg, respectively. The AUC_last values increased in a dose-dependent fashion. The half-life values were 52.00 ± 14.26 h and 66.80 ± 10.91 h at doses of 20 and 30 mg/kg b.w, respectively. Based on the pharmacokinetic data and PK-PD index (T > MIC), i.m. administration of OTC at a dose of 30 mg/kg b.w once per week might be appropriate for the treatment of susceptible bacterial infection in Thai swamp buffaloes.

Probing the in vitro cytotoxicity of the veterinary drug oxytetracycline

The study investigated the effect of oxytetracycline (OTC) on the anti-oxidative defense system, the structure (hemolysis rate and morphology) and function (ATP enzyme activity) of human red blood cells (hRBCs) to investigate the possible toxic mechanism of OTC to hRBCs. The experimental results indicate that OTC can cause a decline in the function of the antioxidant defense system of hRBCs, resulting in oxidative stress. OTC can bring about morphological changes to hRBCs, and further leads to hemolysis, when the concentration of OTC is over 8×10(-5) M (about 164 µg/ml). At a low OTC concentration, below 4×10(-5) M (82 µg/ml), OTC can enhance the activity of ATP enzyme of hRBCs, known as hormesis. However, at a high concentration, above 4×10(-5) M (about 82 µg/ml), the ATP enzymatic activity was inhibited, affecting the function of hRBCs. The estalished mechanism of toxicity of OTC to hRBCs can facilitate a deeper understanding of the toxicity of OTC in vivo.

Delivery of temozolomide to the tumor bed via biodegradable gel matrices in a novel model of intracranial glioma with resection

INTRODUCTION

We have completed in vivo safety and efficacy studies of the use of a novel drug delivery system, a gel matrix-temozolomide formulation that is injected intracranially into the post-resection cavity, as a candidate for glioma therapy.

METHODS

A rat intracranial resection model of C6-GFP intracranial glioma was used for safety and toxicity studies. Biodistribution studies were performed using gel matrix-gallocyanine formulations and were evaluated at various time intervals using real-time analysis of dye distribution. Additionally, the resection model was used to determine the efficacy of gel matrix-temozolomide as compared to blank gel matrix. A subcutaneous human xenograft glioma model was used to further assess the efficacy of gel matrix-temozolomide in reducing the overall tumor load.

RESULTS

Gel matrix-temozolomide exhibited minimal cytotoxicity toward normal brain tissue while displaying high levels of oncolytic activity toward glioma cells. In the intracranial glioma resection and subcutaneous glioma model, administration of gel matrix-temozolomide directly to the tumor bed was well tolerated and effective at reducing the tumor load. A significant reduction of tumor load was observed (P < 0.0001) in the 30% temozolomide group (approximately 95%) as compared to blank control. There was little morbidity and no mortality associated with gel matrix treatment.

CONCLUSIONS

Gel matrix-temozolomide appears to be safe and effective when used in vivo to treat intracranial glioma and warrants further development as a potential adjuvant therapy.

Issues and challenges in developing long-acting veterinary antibiotic formulations

Antibiotics are an important class of therapeutic agents, which are used for the treatment of bacterial infectious diseases in a variety of animal species. Antibiotic therapy varies from treatment period to administration routes, depending on the animal species or the type of the disease being treated. Despite the fact that there are a wide variety of commercially available antibiotics, difficulties and problems associated with the administration of antibiotics to animals still exist. Thus, there is a great need and tremendous opportunity to develop long-acting antibiotic formulations for veterinary applications. In this review article, common approaches used to develop long-acting antibiotic formulations are summarized. The challenges and issues related to the development of these long-acting formulations are also discussed.

Sustained release veterinary parenteral products

Controlled release parenteral dosage forms have application in veterinary medicine. Systems that minimize the need for repeated injections while achieving therapeutic effects for extended periods offer benefits that make commercial development of these products desirable. While some products have already found commercial success, others will result from application of new controlled release technologies. This review highlights the formulation and technology challenges in developing some of these controlled release technologies into products. Further, examples of application of controlled release technologies in the veterinary field are discussed.

Biodegradable polymers and their potential use in parenteral veterinary drug delivery systems

Biodegradable polymers have been extensively studied for numerous drug delivery systems for human health purposes. The ever-increasing value of animals to human society allows the application of pharmaceutical developments in the veterinary field from those developed in human medicine. Although many similarities between the human and animal health industries exist there are also notable differences. This paper provides an insight into the animal health market with regard to the challenges and special considerations associated with veterinary drug delivery. It also gives an overview of biodegradable polymers that are used or have been tested in the veterinary field. The purpose of this paper is to highlight some recent developments in this area and to investigate the directions in which veterinary pharmaceutics is heading. In particular, examples of existing biodegradable veterinary drug delivery systems are presented together with applications including intravaginal devices, injectables and implantable systems.

Slow release of two antibiotics of veterinary interest from PVA hydrogels

Two antibiotics, tylosin tartrate and oxytetracycline hydrochloride, were entrapped in poly(vinyl alcohol) (PVA) hydrogels (MW 31,000-50,000) by a cryogen procedure obtaining a controlled release system suitable for veterinary application. It was found that at a low drug matrix loading (10 mg/ml), the in vitro release rate of both antibiotics could be reduced by a previous freeze drying of the gel, while no reduction in drug rate took place in heavily loaded matrices (300 mg/ml). When PVA hydrogels containing tylosin were administered to rats per os the drug could not be detected in the blood, but it was found in organs,: liver, kidneys, and muscles, for up to 120 h. On the other hand, when the same amount of drug was administered orally as powder, no appreciable organ accumulation was detected, while the drug was found in faeces and urine. These data show that PVA hydrogels can be a suitable slow release system for tylosin administration. Oxytetracycline could also be quantitatively entrapped and released from PVA hydrogels, but once administered per os to rats, it was not detected in blood or organs.