Target species
Horses and ponies (non-food producing).
Indications for use
For the treatment of musculoskeletal disorders in horses and ponies where the anti-inflammatory and analgesic properties of phenylbutazone can offer relief. Examples of conditions normally considered suitable for treatment with phenylbutazone include lameness associated with osteoarthritic conditions, acute and chronic laminitis, bursitis and carpitis, and in the reduction of post-surgical soft tissue reaction.
Contraindications
The therapeutic index of phenylbutazone is low. Do not exceed the stated dose or the duration of treatment.
Do not administer with other non-steroidal anti-inflammatory drugs (NSAIDs) concurrently or within 24 hours of each other.
Do not use in animals suffering from cardiac, hepatic or renal disease; where there is the possibility of gastrointestinal ulceration or bleeding; or where there is evidence of a blood dyscrasia.
Do not use in cases of known hypersensitivity to the active substance or to any of the excipients.
Special warnings for each target species
The clinical effect of phenylbutazone can be evident for at least three days following cessation of administration. This should be borne in mind when examining horses for soundness.
Special precautions for use in animals
Use in any animal under six weeks of age, or in aged animals, may involve additional risks. If such use cannot be avoided, animals may require a reduced dosage and special clinical management.
Avoid use in any dehydrated, hypovolaemic or hypotensive animal as there is a risk of increased toxicity.
It is preferable that NSAIDs which inhibit prostaglandin synthesis are not administered to animals undergoing general anaesthesia until fully recovered.
Response to long term therapy should be monitored at regular intervals by a veterinary practitioner.
NSAIDs can cause inhibition of phagocytosis and hence in the treatment of inflammatory conditions associated with bacterial infections, appropriate concurrent antimicrobial therapy should be instigated.
Special precautions to be taken by the person administering the veterinary medicinal product to animals
The product should be handled with care at all times to reduce the risk of accidental ingestion, skin contact or dust inhalation. If accidental skin or eye contact occurs, the site should be washed immediately with water. If the product is ingested, seek medical advice and show the product packaging.
Advice to doctors: gastric lavage (emesis in children) should be performed urgently. Charcoal haemoperfusion has also been shown to be beneficial. Treatment should then be administered symptomatically.
Adverse reactions
In common with other NSAIDs that inhibit prostaglandin synthesis, there may be gastric and/or renal intolerance. This is usually associated with overdosage and such events are rare. Recovery is usual on cessation of treatment and following the initiation of supportive symptomatic therapy (see Overdose for further information). If adverse reactions occur, treatment shoud be discontinued and the advice of a veterinarian should be sought.
Use during pregnancy and lactation
The safety of phenylbutazone in pregnancy has not been established. Use during pregnancy should be avoided whenever possible, particularly during the first trimester.
Interactions
Some NSAIDs may be highly bound to plasma proteins and compete with other highly bound drugs to produce an increase in non-bound pharmacologically active concentrations which can lead to toxic effects. Concurrent administration of potentially nephrotoxic drugs (e.g. aminoglycoside antibiotics) should be avoided. Gastrointestinal tract ulceration may be exacerbated by corticosteroids in animals given NSAIDs.
Amounts to be administered and administration route
For oral administration only. When mixed with a concentrate feed, the product was shown to be palatable to horses.
The dosage should be adjusted according to the individual animal’s response, but the following may be taken as a guide:
Horses: 450 kg (1000 lb) body weight: the contents of two sachets to be administered twice on day 1 of treatment (equivalent to 8.8 mg/kg/day) followed by the contents of one sachet twice daily for four days (4.4 mg/kg/day), then one sachet daily, or on alternate days, sufficient to keep the horse comfortable (2.2 mg/kg/day).
Ponies: 225 kg (500 lb) body weight, one sachet (4.4 mg/kg) on alternate days.
Discontinue treatment if no response is evident after four to five days treatment.
For ease of administration mix the powder with a small quantity of feed.
Dampening of the veterinary medicinal product in feed 5 minutes prior to feeding has been shown to have no detrimental influence on the palatability of the product. However, the influence of prolonged dampening on palatability or stability of the product is not known.
Overdose
Overdosing may result in gastric and large intestinal ulceration and general enteropathy. Renal papillary damage may also occur with impaired renal function. Subcutaneous oedema, especially under the jaw may become evident due to plasma protein loss.
There is no specific antidote. If signs of possible overdosage occur, treat the animal symptomatically.
The therapeutic index of phenylbutazone is low. In man, charcoal haemoperfusion in conjunction with dopamine has been used successfully to treat overdosage with phenylbutazone, but there is no experience of the use of this technique in the horse.
Withdrawal periods
Not to be used in horses intended for human consumption. Treated horses may never be slaughtered for human consumption. The horse must have been declared as not intended for human consumption under national horse passport legislation.