Stephen J. Hernandez-Divers, BSc(Hons), BVetMed, Dipl RCVS Zoological Medicine
RCVS Specialist in Zoo & Wildlife Medicine (reptiles), Exotic Animal, Wildlife & Zoo Animal Medicine, Department of Small Animal Medicine & Surgery, College of Veterinary Medicine,
University of Georgia, GA, USA
Birds have high metabolic rates that generally require more frequent administration of higher doses than those used in mammals. In addition, fluid, nutritional and temperature support are critical. A heat and humidity controlled incubator with humidifier/nebuliser attached is particularly useful in avian practice.
Birds are acutely sensitive to the toxic effects of medications and it is imperative that an accurate body weight is obtained prior to and during therapy.
Many of the pharmacokinetic studies have been undertaken using poultry and other domesticated avian species. While an increasing number of exotic species pharmacokinetic studies are being undertaken, there are currently relatively few drug studies involving even fewer exotic species. Therefore, in many cases it is necessary to extrapolate from one species to another, either directly or by allometric scaling.
A number of pharmaceutical difficulties arise from the fact that the vast majority of drugs are not specifically marketed for avian species. Thus, factors such as the relatively small size of birds versus the concentration of drugs in available dosage forms, the relatively small muscle mass for intramuscular injections and the unique structure of the digestive and respiratory systems are an added dimension for consideration when attempting to develop optimum drug dosage regimes for birds.
The most commonly used routes of drug administration to birds are orally (i.e., in water, in feed, by syringe, by oesophageal feeding tube) or parenterally (i.e., intraosseous, intravenous, intramuscular, subcutaneous). Intravenous and intraosseous routes are commonly employed for irritant drugs and in emergencies, e.g., critical care fluid therapy. Other practically useful methods of drug administration include nebulization, therapeutic implants and endoscopic remote injection techniques.
Birds do not tolerate topical medications particularly well. Oil based creams cause feather disruption and matting and most birds will groom their plumage until all medication is removed. Dangers of gastro-intestinal and systemic side effects from the ingestion of topical medications definitely exist. In cases where topical treatment is essential it is wise to consider bandaging and temporary restraint techniques (e.g., reduced lighting and neck collars).
In-feed and in-water medications are only really practical on a large scale. Sick birds may eat and drink less and so this method is less reliable and generally not preferred for treating individual patients.
Most birds will attempt to bite an advancing syringe and low volume medication can be easily administered by this method, particularly by owners. For larger volumes it is advisable to administer drugs via a metal or rubber feeding tube placed down the oesophagus, avoiding the glottis and trachea, and into the crop.
a) For crop tubing a psittacine, hold the bird upright with the neck in extension. b) The tube is passed through the left side of the oral cavity and down the oesophagus in the right side of the pharyngeal cavity. The tip of the tube should be palpated to ensure that it is in the crop before delivering fluids or feeding formula. 1-trachea, 2-oesophagus, 3-crop, 4-laryngeal mound, 5-rima glottis, 6-tongue.
From Ritchie, Harrison and Harrison. 1994. Avian Medicine: Principles and Application. Harrison Bird Foods. Pp 392. Reprinted with permission.
For more critical cases involving disease of the mouth, oesophagus, crop or proventriculus, a soft rubber feeding catheter can be surgically placed, transcutaneously, into the proximal oesophagus and down into the proventriculus or ventriculus.
Subcutaneous injection is seldom used due to slow update and less dependable pharmacokinetics. Exceptions include the administration of certain vaccines (e.g., polyoma, pox).
Usually the parenteral route of choice because of dependable pharmacokinetics and rapid uptake. The most common injection sites are the major pectoral (breast) muscles and the iliotibialis (craniolateral thigh) muscles of the pelvic limbs.
Jugular, basilic and medial metatarsal veins are commonly used for intravenous injections. Avian veins tend to be fragile and damage easily. Therefore catheterisation should be considered if frequent access is required. In addition, the ulnar nerve travels alongside the basilic vein and should be carefully avoided.
Intraosseous catheters are technically easier to place and maintain than intravenous catheters. The distal ulnar and proximal tibia are preferred sites. Care is required to avoid all potentially pneumatized bones including the humerus and femur.
Technique for placing an intraosseous catheter in the distal ulnar. a) The thumb is placed in the centre of the ulnar (1) as a guide. b) The catheter is inserted slightly ventral to the dorsal condyle of the distal ulnar (2). The radius (3) and radial carpal bone (4) can be used for orientation. c) The catheter is sutured or taped in place. From Ritchie, Harrison and Harrison. 1994. Avian Medicine: Principles and Application. Harrison Bird Foods. Pp 387. Reprinted with permission.
Respiratory diseases are often complicated by resistant bacteria and fungal infections requiring the use of potentially nephrotoxic antimicrobial drugs. The aerosolisation of these drugs into a fine mist (with particles less than 3 µm in diameter) appears to be beneficial (e.g., amikacin 50 mg in 10 ml saline, amphoteracin B 100 mg in 15 ml saline). Most nebulised drugs (e.g., amikacin, amphoteracin B) are poorly absorbed across the respiratory epithelium, and therefore systemic toxic effects appear less likely. Nebulization should always be combined with systemic therapy.
The use of fine diameter rigid telescopes (Avian and Exotic Endoscopy, Karl Storz Veterinary Endoscopy) has revolutionized avian medicine. In addition, fine injection/aspiration needles permit the endoscopic administration of drugs directly onto or into a lesion. For example, air sac granulomas are usually resistant to antimicrobial therapy and must be debrided before the local application of antimicrobials via the endoscope.
The use of antibiotic impregnated polymethylmethacrylate beads has also been useful for the treatment of osteomyelitis and chronic cellulitis. Aminoglycoside beads are generally preferred and should only be placed following extensive surgical debridement. Beads should be removed once infection has been controlled.
DRUGS AND DOSAGES
Limited space prevents the inclusion of a drug formulary but readers are directed to the references for specific drugs and dosages.
1. Carpenter JW, Mashima TY, Rupiper DJ. 2001. Exotic Animal Formulary. Second edition. WB Saunders, Philadelphia, PA. Pp109-249.
2. Ritchie B, Harrison GJ, Harrison LR. 1994. Avian Medicine: Principles and Application. Harrison Bird Diets, Delray Beach, FL.
3. Journal of Avian Medicine and Surgery. Published by the Association of Avian Veterinarians. Details available from www.aav.org