The presence of minocycline in the tear film of normal horses following oral administration and its anticollagenase activity.

The study investigates the concentration of the antibiotic minocycline in horse tears after oral administration, and determines its effectiveness in directly inhibiting matrix metalloproteinases (MMPs). It was found that minocycline appears in the tears, even though it varied between horses, but was ineffective at inhibiting MMPs at the given concentration.

Methodology

• Five healthy adult ponies were orally administered minocycline at 4 mg/kg every 12 hours for five days.
• At various time intervals, the researchers collected tear samples from the ponies to study the concentration of minocycline.
• The concentration of minocycline in the tears was analyzed using high performance liquid chromatography.
• In order to determine the ability of minocycline to inhibit the action of MMPs, a fluorescence resonance energy transfer investigation was conducted using recombinant human MMP-2 and MMP-9.

Results

• Minocycline was found in the tear samples of all five ponies. However, there was variability in the concentration between different ponies.
• Two hours after the first dosage of minocycline was given, an average concentration of 11.8 μg/mL was observed in the tears.
• Despite the presence of minocycline in the tears, it did not directly inhibit the function of MMP-2 or MMP-9 enzymes at the concentration measured in the tears.

Conclusions

• Minocycline was present in the tears of all ponies at each time point following oral administration. However, one pony consistently had lower levels of minocycline.
• The concentration of minocycline secreted in the tears did not directly inhibit MMP-2 or MMP-9 when tested in vitro.
• The varying concentrations of minocycline and the lack of MMP inhibition suggest that topical application may be needed to attain direct inhibition of MMP with minocycline.