PHENYLBUTAZONE

Bizolin Gel, Butatron TM Oral Gel, Phen-Buta-Vet Inj., Phen-Buta-Vet Tabs, Phenyl Gel-4, Phenylbutazone Inj. Phenylbutazone Inj. 20%, Phenylbutazone Tabs, Phenylzone Paste, Pro-Bute TM Inj., Pro-ButeTM Tabs

DESCRIPTION

Phenylbutazone is a non-steroidal anti-inflammatory drug. It also has analgesic (pain relief) and antipyretic (fever-reducing) activity. The drug acts directly on tissues and its most marked effects are on inflamed tissues.

INDICATIONS

Phenylbutazone is indicated for the treatment of a wide range of musculoskeletal disorders, including muscular sprain and strain, muscular overuse (including both muscular damage and strain/damage of the tendons attaching muscles to bone), tendonitis, acute joint injury/strain/sprain, and arthritic conditions.

Anti-inflammatory drugs do not cure musculoskeletal problems. They do control the inflammation, thereby helping to decrease the ultimate damage and scarring, and making the horse more comfortable during the painful periods.

Pain and inflammation control also serve to make movement more comfortable. This helps prevent any permanent decrease in range of motion of the affected areas so that they do not become too "scarred down." Pain control/exercise must be carefully counterbalanced with the veterinarian's instructions to limit stress and avoid reinjury or worsening injury to damaged areas.

Phenylbutazone also is often used to help control pain from injuries, infections, laminitis, or virtually any other source of pain. Its effectiveness under these conditions will vary widely, depending both on the individual horse and the cause of the pain. It is a reasonable first choice drug for pain control.

Phenylbutazone also is often used to control the fever associated with viral or bacterial infections. Its use under these circumstances may mask the severity of the problem and/or any worsening of symptoms. It should only be used when the veterinarian has determined that symptoms are severe enough to prevent normal eating/drinking, and/or that they are otherwise interfering with the horse's recovery.

Appropriate antibiotic treatment must also be continued.

DOSAGE AND ROUTE OF ADMINISTRATION

Phenylbutazone may be given orally or by the intravenous route. Oral preparations available include tablets (to be crushed and mixed with feed or given with a balling gun), paste, and gel forms.

The maximum manufacturer's recommended intravenous dose is 1-2 grams/1000 Ib daily. The upper dose limit is recommended for initial injection to achieve rapid control of the inflammatory process. This should then be decreased.

The maximum manufacturer's recommended oral dose is 2-4 grams/1000 Ib daily. Because blood levels drop rapidly, it is suggested that the total daily dose be divided and the drug be administered every 8 hours for best effect. Many veterinarians and owners get satisfactory results giving phenylbutazone only once or twice a day.

SPECIAL PRECAUTIONS

Extreme care must be used when phenylbutazone is injected intravenously. Phenylbutazone is extremely irritating to tissues and can cause extensive swelling, pain, tissue damage, and even loss of tissues if injected outside the vein. Repeated injections of phenylbutazone into the same vein may also cause damage or destruction of the vein itself, possibly leading to chronic local swelling and edema of the areas of the body normally drained by the vein that has been damaged.

When giving phenylbutazone orally, follow instructions for proper administration of gel or paste forms. The mouth should be inspected to be sure that it is free of any grain or hay, rinsing if necessary. The medication should be injected on the back of the tongue with the head held slightly elevated. Hold the head in this position or keep the horse on short cross-ties for several minutes after administration of paste or gel. This prevents it from falling out of the horse's mouth, and keeps the horse from spitting it out. Water buckets also should be removed for approximately 15 minutes after administration to prevent the horse from rinsing part or the entire dose out in the water.

When using crushed tablets in feed, the full dose must be consumed to be effective. Most horses will readily accept the drug when mixed in with sweet feed.

For horses that will not take the medicated grain, try mixing the medication in a small amount of molasses and adding this mixture to the grain. If this does not work, a thick mixture can be made of phenylbutazone and molasses, or phenylbutazone and an antacid such as Milk of Magnesia, which is then placed directly onto the back of the horse's tongue.

SIDE EFFECTS/TOXICITY

Overdoses with phenylbutazone can occur relatively easily. Once a blood level of phenylbutazone reaches a toxic level the metabolism of phenylbutazone is inhibited and elimination of the drug is reduced. Overdoses result in mouth and tongue lesions, gastrointestinal ulcers, and possibly hemorrhage. This is particularly a risk with young and stressed horses, or horses ill from other causes.

Damage to the lining of the gastrointestinal tract can be severe enough to cause the horse to leak significant amounts of protein from his blood into the intestine. The lowered blood protein levels result in edema, usually in the legs and along the belly. General symptoms include thirst, decreased appetite, weight loss and weakness that is, in part, secondary to the low protein and low levels of calcium in the blood. Advanced cases progress to renal (kidney) failure and death (see below). Damage to the kidneys also has been associated with prolonged use of phenylbutazone, particularly at high dosages.

Extended use of phenylbutazone also may cause damage to the portal vein in the liver, or other liver abnormalities. Phenylbutazone should not be used in horses known to have preexisting liver, kidney), or gastrointestinal disease.

DRUG INTERACTIONS

Studies in other species show that phenylbutazone is highly bound (attached to) to the proteins in the serum blood, that also serve to carry other drugs. Therefore, concurrent use of other drugs that are normally highly bound to serum proteins may result in greater action and/or toxicity of those other drugs.

Phenylbutazone also increases the anticoagulant effect blood thinning of the drug Coumadin. It should therefore be used with great caution, if at all, in horses receiving Coumadin therapy for conditions such as laminitis or navicular disease.

NSAID toxicities are additive, and NSAIDs should not be used in combination.

PREGNANCY/NURSING

Studies in other animal species have shown that phenylbutazone is potentially toxic to the embryo and can appear in umbilical cord blood and in the milk. Caution is therefore advised in using phenylbutazone in pregnant or nursing mares.

DRUG TESTING

Detection Time Information: Phenylbutazone's pharmacological effects are not thought of as lasting longer than about 24 hours after a clinical dose, particularly an IV dose. Phenylbutazone or its metabolites may be detected in plasma and particularly in urine for longer periods (up to 7 days or longer) after administration of a course of phenylbutazone therapy. The ARCI-recommended plasma level threshold or tolerance level for phenylbutazone is 5 mcg/ml in blood. The Canadian authorities report a 4-day detection time for this drug in horses, while Australian work reports a 5-day detection time.