Phenylbutazone concentrations in synovial fluid following administration via intravenous regional limb perfusion in the forelimbs of six adult horses.

This research study analyzed the effect of a pain-relief drug, phenylbutazone (PBZ), on horses when administered through intravenous regional limb perfusion (IVRLP). The intent was to understand the drug’s concentration in the horses’ joint fluids and the local complications that might occur with its use. The results showed no significant advantages over the use of systemic, or full-body, administration of the drug.

Research Objectives and Methodology

• The main aim of this study was to understand the pharmacological effects of the non-steroidal anti-inflammatory drug (NSAID), phenylbutazone, when delivered via IVRLP, a localized administration technique in horses. This method was thought to be potentially less harmful than systemic (whole body) administration, which can cause negative gastrointestinal and kidney effects.
• This study involved six healthy adult horses. In each horse, one forelimb was randomly selected for PBZ-IVRLP treatment, while the other received a placebo treatment for comparison. The concentration of PBZ in the blood and joint fluid was measured at several timepoints after the treatment.
• Local complications related to the treatment were monitored and evaluated for up to 7 days, using both physical examination and ultrasound imaging. Post-mortem histology (microscopic study of tissue structure) was performed on both forelimbs at the treatment sites after the horses were euthanized on the seventh day.

Research Findings

• The pharmacokinetic analysis showed lower PBZ concentration in the joint fluid compared to the blood at any given time point. This suggests that the drug was not as effectively targeted to the joint tissue as hoped with this localized administration technique.
• Physical and ultrasound assessments found no significant differences between the treated and placebo limbs, suggesting that PBZ-IVRLP treatment did not cause drastic changes or complications at the site of drug administration.
• However, various local complications were identified via post-mortem histological analysis. These included hemorrhage and edema (swelling), perivasculitis (inflammation around blood vessels), and a resolving blood clot in one horse’s treatment limb, while another horse showed severe inflammation and infection (fibrinosuppurative dermatitis/panniculitis) in the placebo limb.

Conclusions

• The study concluded that administering PBZ via IVRLP at a dose of 2.2mg/kg showed no significant advantage over systemic administration as far as the concentration of the drug in the joint fluid was concerned.
• The occurrence of local complications in both the treated and placebo limbs also suggests that the method of administration might not be any safer or less harmful than whole-body treatment.