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Piroxicam for Veterinary Use
by Barbara Forney, VMD
Piroxicam is an NSAID that is used to treat some cancers in dogs and cats and, to a lesser degree, for pain due to osteoarthritis. Piroxicam is a nonselective cyclooxygenase (COX) inhibitor with inhibitory effects on both COX-1 and COX-2. COX-1 produces prostaglandins that regulate homeostasis, allowing the kidney to respond to hypotension and protect the GI tract. COX-2 produces the prostaglandins that are increased in the presence of inflammation. COX-2 is upregulated in many types of tumors, including nasal epithelial tumors, mammary tumors, colorectal tumorsoral squamous cell carcinomaoral melanoma, prostatic carcinoma, transitional cell carcinoma (TCC) of the urinary bladder and osteosarcoma.There also is some research that COX-1 over expression plays a role in as many as 39% of canine TCC incidences. Although the mechanism of action is not understood completely, COX-2 inhibitors may affect tumor cell apoptosis and disrupt tumor angiogenesis.
Like other NSAIDs, piroxicam has anti-inflammatory, analgesic and antipyretic activity. It is used less commonly as a classic NSAID for pain relief because there are other drugs with fewer side effects.
Dogs and Cats
Piroxicam is used within a variety of protocols to treat TCC, squamous cell carcinoma (oral and cutaneous), hemangiosarcoma, prostatic carcinoma and some rectal neoplasms. Many protocols combine piroxicam with a chemotherapeutic drug such as cisplatin or mitoxantrone. In one study of dogs with TCC of the bladder, 35.4% had a measurable response to combined chemotherapy and piroxicam, while 75% showed subjective improvement. Mean survival time (MST) for dogs with TCC treated with the combination of piroxicam and mitoxantrone was just under a year. Radiation therapy may be added to piroxicam and mitoxantrone protocols for TCC.
Piroxicam is thought to have a positive effect on survival time for prostatic carcinoma (MST=6.9 months). Treatment of oral squamous cell carcinoma with cisplatin and piroxicam resulted in a 56% response rate and a MST of almost eight months. There are additional concerns regarding renal toxicity with the drug combination of cisplatin and piroxicam (as high as 86% in one study). The use of piroxicam suppositories for palliative treatment of rectal cancer in dogs is well accepted for the improvement of quality of life. Piroxicam does not appear to confer additional benefits when combined with doxorubicin to treat lymphoma.
Piroxicam is used in cats as an adjunctive therapy to treat TCC of the bladder and oral squamous cell carcinoma. The half-life of piroxicam in the cat is 12 to 13 hours, which is shorter than the 37 to 40 hour half-life in dogs.
Piroxicam is well-absorbed orally and the absorption is not affected by the presence of antacids. It should be given with food to decrease the likelihood of GI ulceration. Piroxicam is excreted primarily in the urine and only about 1% of the plasma level is found in milk. Piroxicam may be combined with opioid analgesic drugs to manage pain in cancer patients. NSAIDs provide synergistic pain relief with opioid analgesics allowing for a lower dose which may minimize the sedating side effects.
Piroxicam Side Effects
Side effects may include gastrointestinal irritation and ulceration and nephrotoxicity.
- Piroxicam has a narrow margin of safety due to GI and renal side effects. Piroxicam should not be used in dehydrated animals and fluid supplementation may be warranted.
- Based on studies in humans, it should be used with additional caution in dogs with decreased cardiac function.
- Animals taking piroxicam for extended periods should be monitored for GI bleeding and be followed for renal and liver function.
- Aminoglycoside antibiotics, cisplatin may increase the risk of renal toxicity.
- Aspirin, corticosteroids, biphosphonates may increase the risk of GI ulceration.
- Aspirin, anticoagulants may increase the risk of bleeding.
- Piroxicam is highly protein bound and may affect the serum levels or duration of action of other highly protein bound drugs including phenytoin, valproic acidoral antacids, salicylates, sulfonamides and sulfonylurea antidiabetic compounds.
- Piroxicam may decrease the effects of furosemide.
- Methotrexate should not be combined with piroxicam due to potential severe toxicity.
If the overdose is recognized promptly, GI emptying with emetics and activated charcoal is warranted. GI protectants against GI ulceration and fluid diuresis for renal protection also may be appropriate.
About the Author
Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.
She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
You can purchase books by Dr. Forney at www.exclusivelyequine.com
Wedgewood Pharmacy's compounded veterinary preparations are not intended for use in food and food-producing animals.