Administration Method Does Not Affect Antibiotic Levels After IVRLP

Intravenous regional limb perfusion (IVRLP) offers a simple, cost-effective method of delivering high concentrations of antibiotics to a horse’s distal limb without unwanted systemic effects. A common indication for IVRLP is a traumatic wound involving synovial structures, often infected with Staphylococcus, Enterobacteriaceae, and Enterococcus. For these pathogens, amikacin sulfate is an ideal antimicrobial because it has a good spectrum of activity.  

“When amikacin is administered via IVRLP, we can achieve target tissue concentrations that exceed the mean inhibitory concentration of the target bacteria,” explained Stephanie Ortiz-Gutierrez, MVZ, from the University of California, Davis.   

There are, however, different methods for administering perfusate, attempting to maximize tissue (e.g., synovial) levels. These include applying a tourniquet, injection characteristics, and altering time and volume of perfusate, among others.  

Study on IVRLP Methods

Ortiz-Gutierrez and colleagues compared two methods of administering the perfusate (amikacin) when performing IVRLP:  

1. Administering 2 grams of amikacin followed by 52 mL saline. 

2. Diluting 2 grams of amikacin to 60 mL with saline for administration.  

The study involved six healthy, non-lame horses. A regional nerve block was performed, and horses were sedated. A tourniquet and catheter were placed in the cephalic vein in the proximal antebrachium, and injections were administered over a five-minute period. The tourniquet was removed 30 minutes after the injection.  

Amikacin concentrations were determined by a fluorescence polarization immunoassay every five minutes from synovial fluid collected from the radiocarpal joint. The goal was to achieve target concentrations > 160 µg/mL.  

Study Findings

“No systemic or local complications were observed in this study, and no differences in Cmax, plasma amikacin concentrations, peak synovial concentrations, or Tmax were appreciated,” said Ortiz-Gutierrez. “All horses reached the target minimum synovial concentration of 160 mg/mL.” 

The study authors did find higher peak synovial fluid amikacin levels than in previous studies. Ortiz-Gutierrez said this could be because she administered the antibiotic over five minutes whereas in other studies the researchers administered the medication over only one to three minutes.  
 
“It seems prudent to deliver perfusate slowly,” she advised.  

Even though both methods achieved adequate synovial fluid amikacin concentrations (160mg/mL), she suggested one advantage to administering the amikacin alone first (protocol one), rather than diluted in a larger volume, is the horse has a better chance of receiving the amikacin via IVRLP if the procedure has to be aborted.  

One limitation to the study was that it involved healthy horses, which might have different pharmacokinetic/dynamics than horses with inflamed joints.

Medical coverage from the 2025 AAEP Convention is brought to you by American Regent Animal Health.

Related Reading

• Disease Du Jour: Regional Limb Perfusions
• Mastering Regional Limb Perfusions in Horses
• Chlorhexidine Flush: Potential Treatment for Septic Arthritis in Horses?

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