Objective—To examine the distribution of water in hoof wall specimens of horses via nuclear magnetic resonance (NMR) microscopy and determine changes in water distribution during hydration.
Sample—4 hoof wall specimens (2 obtained from the dorsum and 1 each obtained from the lateral quarter and lateral heel regions) of the stratum medium of healthy hooves of 1 horse.
Procedures—Equine hoof wall specimens were examined via NMR microscopy. Proton density–weighted 3-D images were acquired. Changes during water absorption were assessed on sequential images.
Results—The inner zone of the stratum medium had higher signals than did the outer zone. Areas of high signal intensity were evident in transverse images; these corresponded to the distribution of horn tubules. During water absorption, the increase in signal intensity started at the bottom of a specimen and extended to the upper region; it maintained the localization pattern observed before hydration. The relationship between the local maximal signals in areas corresponding to the horn tubules and minimal signal intensities in areas corresponding to the intertubular horn was similar and maintained approximately a linear distribution.
Conclusions and Clinical Relevance—Based on the premise that signal intensity reflects water content, hydration in the equine hoof wall during water absorption occurred concurrently in the tubules and intertubular horn, and there was maintenance of the original water gradients. This technique can be applied for the assessment of pathophysiologic changes in the hoof wall on the basis of its hydration properties.
To determine plasma pharmacokinetics of metronidazole and imipenem following administration of a single dose PO (metronidazole, 15 mg/kg) or IV (imipenem, 10 mg/kg) in healthy Thoroughbreds and simulate pleural fluid concentrations following multiple dose administration every 8 hours.
4 healthy Thoroughbreds.
Metronidazole and imipenem were administered, and samples of plasma and pleural fluid were collected at predetermined time points. Minimum concentrations of metronidazole and imipenem that inhibited growth of 90% of isolates (MIC90), including 22 clinical Bacteroides isolates from horses with pleuropneumonia, were calculated. For the computer simulation, the target ratio for area under the pleural fluid concentration-versus-time curve during 24 hours to the MIC90 for metronidazole was > 70, and the target percentage of time per day that the pleural fluid concentration of imipenem exceeded the MIC90 was > 50%.
Mean ± SD pleural fluid concentrations of metronidazole and imipenem were 12.7 ± 3.3 μg/mL and 12.1 ± 0.9 μg/mL, respectively, 1 hour after administration and 4.9 ± 0.85 μg/mL and 0.3 ± 0.08 μg/mL, respectively, 8 hours after administration. For both antimicrobials, concentrations in the pleural fluid and plasma were similar. The ratio for area under the pleural fluid concentration-versus-time curve during 24 hours to the MIC90 for metronidazole was 84.9, and the percentage of time per day the pleural fluid concentration of imipenem exceeded the MIC90 was 70.9%.
CONCLUSIONS AND CLINICAL RELEVANCE
Results suggested that administration of metronidazole (15 mg/kg, PO, q 8 h) or imipenem (10 mg/kg, IV, q 8 h) resulted in their accumulation in the pleural fluid in healthy horses and concentrations were likely to be effective for the treatment of pneumonia and pleuropneumonia caused by Bacteroides spp.