Stability of penicillin G, ampicillin, amikacin and oxytetracycline and their interactions with food in in vitro simulated equine gastrointestinal contents.

The research article discusses the stability and degradation rates of various antibiotics, specifically penicillin G, ampicillin, amikacin, and oxytetracycline, along with their interaction with food in a simulated equine gastrointestinal environment.

Antibiotic Stability in Gastric pH

• The scientists simulated the acidic environment of the equine stomach using a chloride buffer at pH 1.9. Within this environment, they observed different levels of degradation for the four tested antibiotics.
• Penicillin G and amikacin showed substantial degradation after one hour of incubation – 84.7% for penicillin G and 14.4% for amikacin.
• On the other hand, ampicillin and oxytetracycline demonstrated significant stability under the same conditions, showing no signs of degradation.

Antibiotic Stability in Equine Caecal Liquor

• The study also looked at the stability of the antibiotics within equine caecal liquor, a fluid found in the horse’s cecum, over a span of 24 hours.
• Initially, penicillin and ampicillin appeared to be stable, retaining more than 90% of their original concentration after three hours.
• However, after 24 hours, a degradation of about 65% was noted for both antibiotics.
• Oxytetracycline and amikacin showed better stability, with more than 80% of their initial concentrations remaining after 24 hours of incubation.
• Additionally, the research found that the presence of these antibiotics did not affect the concentration of short-chain fatty acids in the equine caecal liquor.

Antibiotic Interaction with Hay

• The researchers investigated how the antibiotics interact with food, specifically hay, as part of a horse’s diet. They studied this by incubating the antibiotics with hay in buffers at pH 1.9 and pH 7.0.
• Results showed that large amounts of penicillin G and amikacin became bound to hay in both acidic (pH 1.9) and neutral (pH 7.0) conditions – over 84% in each case.
• A significant difference was seen with ampicillin, which did not bind to hay in an acidic environment but showed more than a 60% binding rate in a neutral pH environment.

The findings of this study provide crucial insights into how these antibiotics perform within the digestive environment of horses, including their interaction with food. The observed degradation rates and binding behaviors can influence decisions on the optimal timing and conditions for antibiotic administration.