The isolated perfused equine distal limb as an ex vivo model for pharmacokinetic studies.

The research article discusses the development of an ex vivo model using the distal forelimb of a horse for studying the pharmacokinetics of substances used for intra-articular injections, with betamethasone as an early example.

Development of the Ex Vivo Model

• The study talks about developing an ex vivo model for studying the pharmacokinetic properties of substances used in intra-articular injections to treat joint-related lameness in horses. Intra-articular injections are common forms of treatment but their pharmacokinetic properties, or how the substance moves within the body, are not well understood.
• For the model, the distal forelimbs of slaughtered horses were isolated. These isolated forelimbs were perfused with a gassed Tyrode solution for up to eight hours. Tyrode’s solution is a solution of eight salts in water and is often used for perfusing mammalian organs.
• Tissue viability was confirmed using measurements of glucose consumption, lactate production, and lactate dehydrogenase activity in the perfusate, thus demonstrating that the model effectively supports the tissues.

Implementation of the Model and Results

• The study then presents the first implementation of this model, testing the articular efflux rate of betamethasone. Betamethasone is a glucocorticoid steroid often used for joint disease in horses.
• The medicine was administered in the form of betamethasone disodium phosphate, and its concentration was measured using high-performance liquid chromatography, a common method for analyzing mixtures of organic compounds.
• The average betamethasone efflux rate per minute was calculated to be approximately 5.1 μg/min, seven and a half hours after intra-articular application, it was found that about 2.3 mg of betamethasone had left the joint via the radial vein.

Benefits of the Model

• One significant point in the study is the ethical advantage of this model. Using an ex vivo model means the experiments can be conducted without harming live animals.
• This model is also inexpensive to set up, enabling versatile study of various pharmacological issues.