Pharmacokinetics and pharmacodynamics of enrofloxacin and a low dose of amikacin administered via regional intravenous limb perfusion in standing horses.

The research evaluates the effects and efficacy of administering enrofloxacin and a low dosage of amikacin to horses through a method called regional IV limb perfusion (RILP). Results indicate that enrofloxacin was more effective, maintaining inhibitory concentrations for up to 36 hours in certain tissues, suggesting its potential use for treating orthopedic infections. Amikacin, however, didn’t reach effective tissue concentrations, indicating a need for a higher dosage.

Study Design and Methods

• The study focused on the effects of enrofloxacin (1.5 mg/kg) and amikacin (250 mg), administered to two groups of seven standing horses each, through a procedure known as regional IV limb perfusion (RILP).
• This procedure involved applying a tourniquet to one forelimb of each horse, followed by the relevant drug administration.
• Interstitial fluid samples from the bone marrow (BMIF) of the third metacarpal bone, local subcutaneous tissues (STIF), blood, and synovial fluid of the radiocarpal joint were collected before (at time 0) and at regular intervals after the tourniquet’s release.
• These samples were then analyzed to determine drug concentrations.

Pharmacokinetic-Pharmacodynamic Analyses

• The minimum inhibitory concentrations (MICs) of the drugs were set at 16 microg/mL for amikacin and 0.5 microg/mL for enrofloxacin.
• Enrofloxacin and amikacin concentrations in synovial fluid were highest immediately after the tourniquet release; median values were 13.22 microg/mL and 26.2 microg/mL, respectively.
• Enrofloxacin maintained effective concentrations in STIF and synovial fluid for around 24 hours and in BMIF for 36 hours.
• No effective concentrations of amikacin that exceeded the MIC were detected in any of the samples.

Results and Recommendations

• Three horses developed vasculitis after being administered enrofloxacin through RILP.
• The findings confirmed that therapeutic concentrations of enrofloxacin were achieved in all samples, making it a viable treatment option for horses with orthopedic infections.
• However, due to the risk of vasculitis, care must be taken when administering the drug.
• The study also indicated that amikacin at the given dose (250 mg) didn’t reach effective tissue concentrations, suggesting a need for higher dosages to achieve therapeutic effects.