High-Performance Liquid Chromatography Determination of Meloxicam and Piroxicam with Ultraviolet Detection

A simple accurate and sensitive high-performance liquid chromatographic method for the determination of meloxicam and piroxicam concentrations in small volume plasma samples has been developed. Following a liquid extraction using chloroform, samples were separated by reversed-phase high-performance liquid chromatography on an XBridge C18 column (4.6？×？250？mm) and quantified using ultraviolet detection at 360？nm. The mobile phase was a mixture of water with glacial acetic acid (pH 3.0) and acetonitrile (50？:？50), with a flow rate of 1.0？mL/min. The standard curve ranged from 5 to 10,000？ng/mL for meloxicam in bearded dragon (Pogona vitticeps) plasma and piroxicam in crane (Grus rubicunda) plasma. Intra- and interassay variability for meloxicam and piroxicam were less than 10% and the average recovery was greater than 90% for both drugs. This method was developed in bearded dragon and crane plasma and should be applicable to any species, making it useful for those investigators dealing with small sample volumes, particularly when conducting pharmacokinetics studies which require multiple sampling from the same animal. 1. Introduction Meloxicam, 4-hydroxy-2-methyl-N-(5-methyl-1,3-thiazol-2-yl)-1,1-dioxo-1λ6,2-benzothiazine-3-carboxamide, and piroxicam, 4-hydroxy-2-methyl-1,1-dioxo-N-pyridin-2-yl-1λ6,2-benzothiazine-3-carboxamide, are nonsteroidal anti-inflammatory drugs (NSAIDs) with analgesic properties. They are generally used to treat osteoarthritis and rheumatoid arthritis; however, they can be used for other painful conditions such as injuries, cancer surgery, and dental infections. Meloxicam preferentially inhibits the cyclooxygenase-2 (COX-2) enzyme over COX-1. The ability to only inhibit the inflammatory COX proved to be revolutionary for pain management. The introduction of COX-2 preferential NSAIDs has reduced stomach and intestinal side effects. While piroxicam is used to treat painful conditions, it has recently been used in a variety of protocols to treat squamous cell carcinoma and hemangiosarcoma. Meloxicam can be metabolized to as many as four biologically inactive metabolites depending on the species; however, the 5-hydroxy methyl derivative is the most common metabolite. Piroxicam metabolism occurs via a cytochrome P450 2C isoform to multiple biologically inactive metabolites, with 5-hydroxy-prioxicam being the most common. Nonsteroidal anti-inflammatory drugs are commonly used in large and small veterinary practices for relief of pain, fever, and inflammation. Increasing public awareness of animal welfare will likely continue to make