Plasma disposition of amikacin and interactions with gastrointestinal microflora in Equidae following intravenous and oral administration.

The study investigates how a drug called amikacin behaves in the bodies of horses, ponies and donkeys, either when injected directly into the blood or administered orally. It also explores whether the drug affects the gastrointestinal bacteria and other factors in these animals.

Amikacin Disposition in Plasma

• The researchers administered amikacin to horses, ponies and donkeys either intravenously (i.v.) or orally.
• Following intravenous administration, amikacin was detectable in the plasma of horses and donkeys for up to 12 hours and in ponies for up to 8 hours. The detectable limit of the drug in plasma was found to be more than 0.02 micrograms/ml.
• The elimination half-life of the drug, which is the time taken for blood concentration of the drug to reduce by half, was found to be 2.8 hours in horses, 1.6 hours in ponies and 1.9 hours in donkeys. The half-life varies due to differences in metabolism among these animals.
• The study suggests that, based on the elimination patterns, the appropriate dosage intervals of amikacin administered intravenously at a dose rate of 6 mg/kg would be every 8 hours for horses and every 6 hours for ponies and donkeys.

Amikacin Interactions with Gastrointestinal Microflora

• The study observed no significant changes in caecal liquor pH, the number of viable bacteria isolated, or the short chain fatty acid (SCFA) concentrations (which are products of microbial fermentation) in caecal liquor and faeces following intravenous administration of the drug.
• When amikacin was administered orally via a nasogastric tube in ponies, it was not detectable in plasma but was present at high concentrations in the caecal liquor (ranging from 16.2 to 99.4 micrograms/ml). This indicates that oral administration of the drug may not effectively reach the systemic circulation in these animals, but it heavily impacts the caecal region of the gut where it accumulates.
• Despite the high concentrations of amikacin in the caecal liquor following oral administration, only slight changes were observed in the number of viable bacteria. However, there was a marked reduction in caecal liquor pH to below 6.6, indicating an acidic shift in the gut environment, although short chain fatty acid concentrations remained largely the same.
• The study found no significant changes in faecal SCFA concentrations, dry matter content or consistency following oral administration of amikacin.

The findings suggest that the method of administration can significantly influence the distribution and impact of amikacin in Equidae, with potential effects on the gut environment particularly with oral administration. Further studies are needed to explore the implications of these findings and the potential effects on the overall health of these animals.