The equine lower limb can be a notoriously difficult part of the horse to treat with systemic antibiotics, mainly because the limited blood supply in this area makes it tough to deliver enough antibiotic to be effective. One option for getting a lot of antibiotic into lower limb and hoof tissues is regional limb perfusion (RLP), in which a veternarian places a tourniquet on the limb and injects antibiotic into a vein below the tourniquet. Isolating the blood supply via the tourniquet for a brief period (usually 30 minutes or so) keeps the antibiotic in the lower limb long enough for the antibiotic to migrate into the tissues of the limb.
So far so good; but might using one vein or another yield higher concentrations of antibiotic in the target tissues and, thus, better antibiotic activity?
Researchers from the University of Tennessee set out to answer that question and presented their results at the 2009 American Association of Equine Practitioners Convention, held Dec. 5-9 in Las Vegas, Nev. Frank Andrews, DVM, MS, Dipl. ACVIM, director of the Equine Health Studies Program at Louisiana State University, presented the study for lead author Gal Kelmer, DVM, MS, Dipl. ACVS, who was unable to attend the convention.
While veterinarians normally perform regional limb perfusion using injections into the palmar digital vein (just behind the fetlock in this study), the researchers explained in the study that using the cephalic and saphenous veins higher up in the limb (more proximal) provides several benefits:
1) These locations allow regional limb perfusion even with a cast on the limb, since they are injected above (proximal to) it.
2) It is easy to place and maintain a catheter in these veins; this yields multiple advantages such as avoiding daily vein puncture; being easy on needle-shy horses; providing a simpler RLP procedure that can be done by less trained personnel, reducing clinician workload; and having venous access for a longer time since the vein is not punctured daily (this can be crucial in persistent infections).
The researchers used 19 horses for the study, and they found that using either the saphenous or cephalic vein yielded high concentrations of antibiotic in the fetlock joint that were comparable to those achieved in other studies for the palmar digital vein. The investigators on the current study actually found the concentrations of antibiotic in the fetlock joint were lower when using the palmar digital vein, but Kelmer notes that this might have been due to tourniquet failure, as researchers in other studies have found more success with this location.
"High fetlock joint concentrations of amikacin (the antibiotic used) were attained by regional limb perfusion injected through the proximal (saphenous and cephalic) veins," summarized Andrews. "However, in this study, amikacin concentrations in the fetlock joint were suboptimal with palmar digital vein injection regional limb perfusion using this technique."
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.