“Bute” (phenylbutazone) and Banamine® (flunixin meglumine) are both anti-inflammatory, non-steroidal anti-inflammatory drugs (NSAIDS) that are commonly given to horses to address pain. They are two medications that I try to have on hand (especially Banamine) because when you need them, you need them right now.
I’ve always used Bute for musculoskeletal pain. If a horse is lame, for example, your vet might suggest Bute for a couple of days. It should not be used for long term pain treatment as It is likely to cause ulcers, especially in the large colon. Bute is usually dispensed in a powder or paste form.
Banamine is a drug that is most commonly given for colic relief as it has extra anti-inflammatory benefits that make it helpful for treating intestinal problems. Unlike Bute, when you give Banamine to a horse you can see the results within a half hour — a colicky horse often shows significant relief. Banamine is usually dispensed as a past although it can also be given intravenously and some people give it intramuscularly, although that can be irritating to tissues.
For more information, there is an excellent series of articles on the differences between the two drugs on Behind the Bit.
Bute vs. Banamine: Banamine, Part 2