Based on structure, most NSAID can be divided into 2 broad groups—carboxylic acid and enolic acid derivatives. The main subgroups of enolic acids are the pyrazolones (phenylbutazone) and the oxicams (meloxicam, piroxicam). Carboxylic acid subgroups include the salicylates (aspirin), propionic acids (ibuprofen, naproxen, carprofen, ketoprofen, and vedaprofen), anthranilic acids (tolfenamic and medofenamic acids), phenylacetic acids (acetaminophen), and aminonicotinic acids (flunixin).