Pharmacokinetics of a long-acting oxytetracycline-polyethylene glycol formulation in horses.

The research article investigates the pharmacokinetics and tolerability of a long-acting oxytetracycline-polyethylene glycol (PEG) formulation in horses. This treatment is often used in suspected cases of equine monocytic ehrlichiosis and has been conditionally determined to be less harsh when administered to horses.

About Oxytetracycline

• Oxytetracycline is a broad-spectrum antimicrobial not frequently used in horses due to potential harmful gastrointestinal effects.
• Despite these concerns, oxytetracycline is still the preferred treatment for horses suspected or confirmed to have equine monocytic ehrlichiosis, a disease also known as Potomac Horse Fever.
• This antimicrobial is also used for equine granulocytic ehrlichiosis, an emerging zoonotic disease. This is because oxytetracycline effectively neutralizes the resistance of Ehrlichia spp., the bacteria causing these diseases.

Oxytetracycline Formulations

• Oxytetracycline is administered parenterally and is typically formulated as a hydrochloride salt. This compound is integrated with vehicles such as propylene glycol, polyvinyl pyrrolidone, 2-pyrrolidone, or N,N-dimethylacetamide.
• Oxytetracycline hydrochloride combined with 2-pyrrolidone or N,N-dimethylacetamide produces prolonged serum and tissue concentrations, qualifying it as ‘long-acting’.
• While these oxytetracycline hydrochloride solutions can be given to horses, they must be carefully administered through slow intravenous injection to avoid causing circulatory collapse.
• Long-acting oxytetracycline formulations create severe irritation when injected intramuscularly into horses, so this method is often avoided.

The Study

• The study focused on evaluating the pharmacokinetics and tolerability of an oxytetracycline formulation in a polyethylene glycol (PEG) carrier. This newly developed formulation- Bio-Mycin 200 is currently approved for treating respiratory diseases in cattle and swine.
• The researchers tested this formulation with minimal tissue irritation on six American Quarter horses aged 2 to 5 years, recording the effects of both intravenous and intramuscular administration.