Applying the principles of intravenous drug delivery

How are the pharmacologic principles for intravenous drug delivery applied? Joe Smith, DVM, MPS, PhD, DACVIM, DACVCP, cVMA, an associate professor at the University of Tennessee College of Veterinary Medicine in Knoxville, explains in a dvm360 interview recorded at the 2026 American College of Veterinary Internal Medicine Forum in Seattle, Washington. Smith, who specializes in farm animal medicine and veterinary clinical pharmacology, discussed these principles during a recent lecture at the meeting. In this video, he talks about intravenous regional limb perfusion and the appropriate use of intravenous drugs for different patient species.

The following is a transcript of this video, a portion of the interview:

Joe Smith, DVM, MPS, PhD, DACVIM, DACVCP, cVMA: Intravenous regional limb perfusion is a technique that's been fascinating me for a while. For this technique, if you're not familiar with it, we apply a tourniquet above the distal aspect of the limb for a very short period of time, then we place a catheter into the vein. And we will put drugs directly into the vein while we have that tourniquet on there, so that we're increasing the pressure within the veins, which will then drive those drugs into the tissues around the veins instead of it circulating throughout the body. This allows us to treat a very specific part of the patient in a very precise way.

One [way] I think this precision is very useful is [in] antimicrobial stewardship. If we wanted to give antibiotics for a distal limb infection to the entire animal, we're going to have to give a very, very high dose, [whereas] if we use a regional limb perfusion technique, we can give a very small dose overall that will be very concentrated in those tissues. And it's not just for antimicrobials to treat infection, either. We can do this with anti-inflammatories…[and] with local anesthetics.

This technique [was] developed from the human oncology side of things, where they'll do very unique things to treat a tumor that might be in a limb and get very high levels of chemotherapy in that limb without actually treating the entire patient with large amounts of chemotherapy. So the principles there are typically the size of the molecule: A smaller molecule typically crosses barriers much farther, [and] charge and uncharged molecule[s] typically cross barriers much better. Lipid solubility comes into play, as well. Typically, a drug that can be dissolved in lipid is going to be able to perfuse into the tissues. But all these different factors interact with each other, and in a way, that fascinates me, because we can see situations where maybe a drug that has a very large molecular size but is very lipid soluble will work very well for regional limb perfusion.

There's been a new paper with tulathromycin, which is a very large molecule antimicrobial that's actually absorbed pretty decently into the tissues around the limb when we deliver it by that technique, whereas before then, we were using smaller molecules [such as] ampicillin…just because we thought they would get through those blood vessels into the tissues better.