Horse Medications - Their Use and Contraindications
Table of Contents
Veterinarians are very influential in the decision making and activities related to horse health. We have to remember the following facts when dispensing medications (indicated in italics):
When a veterinarian is called in to diagnose a problem with an owner's horse, it is a very stressful time. Owners often focus on their animal's problem, especially if it is colic or a major injury. When veterinarians are dispensing a medication, it is time consuming, but necessary, that owners focus on hearing and understanding the instructions. It is the veterinarian's responsibility to ensure that owners understand what the medication is, how often it should be used and the route of administration. Some medications may need to be given 2 or 3 times daily. Is the owner or barn manager available to give the medication every 8 or 12 hours for 5 or 7 days in a row?
Since many of our horse owners are new to the industry, veterinarians need to show the owner how to load a syringe, where and how a needle should be placed and ensure that the owner can give the medication without endangering the health of the horse or themselves. The neck bones run just above the jugular furrow, not just under the mane. The landmarks for injection sites should be clearly recognized. The injection triangle in the neck is easily identified as illustrated in Figure 1.
Figure 1. The Most Common Intramuscular Injection Points of the Horse
Women of all ages, but particularly teenage women, are very active in all levels and disciplines of the equine industry. Some medications that are commonly used in and around the stable can affect the menstrual cycle of women or impact on their health, including pregnancy.
Products such as Regu-Mate® can be absorbed after skin contact and especially if wearing latex gloves. The manufacturer warns that the following people should not handle this drug: pregnant women, those with thrombophlebitis, coronary disease, women with breast cancer, estrogen dependant neoplasia or undiagnosed vaginal bleeding (1). Veterinarians should provide owners with a written protocol for the proper handling of medicines. This protocol can be hung in the barn for future reference. For further information, refer to the factsheet, Human Health Concerns when Working with Medications around Horses.
The internet has dramatically increased peoples' access to information. At the touch of a fingertip, one can obtain information on virtually every disease. Unfortunately, this leads to self-diagnosis, misuse of medications, use of homeopathic products of variable and often unknown effects and a blur of what are proper and recognized treatment regimens. Penicillin G procaine and similar penicillin products are available in two strengths, 200,000 and 300,000 IU per mL. The recommended dose ranges from 10,000 - 20,000 IU/kg intramuscularly every 6 hours to 22,000 - 40,000 IU/kg every 12 hours (1). For the owner, the calculation of the correct dosage can be a major obstacle. The following is an example. When using the 300,000 IU/mL penicillin and when recommended to use the 22,000 units per kg dosage, divide the strength (300,000 IU per mL) by the dosage per unit of weight (22,000 IU per kg) to get the dosage of 1 mL per 13.6 kg (300,000/22,000 = 13.6). Many owners have difficulty understanding that a milliliter (mL) is the same as a cubic centimeter (cc).
Instructions should be given, clearly indicating the dosage (e.g., 10 mL), how the medication is to be given (e.g., by the intramuscular or subcutaneous route) and the frequency and length of usage (e.g., every 12 hours for "X" number of days). The number of days will depend on the response of the bacteria causing the infection to the medication. This is determined by the resolution of clinical signs (e.g., a return to a normal rate and depth of breathing) and a return to normal core body temperature (38 + 0.5°C).
Over the past ten years, society in general and, more specifically, horse owners are more conscious of the impact of improper antibiotic use, the ground water and environmental impact of manure run-off. The avermectin products, such as Eqvalan® and Quest, are excreted from the horse and are reported to be quickly bonded to the soil. Approximately one million doses of these dewormers are used in Ontario each year and, since residues may adversely affect fish and water-borne organisms, safe disposal of residual materials, such as syringes, is important.
As we get older, the print on medication bottles is getting smaller and harder to read, especially if we are not carrying our glasses to the barn.
The size of print used on bottles of medications seems to be getting smaller and smaller. Those of us that are over forty and having a struggle with the "length of the arm" when reading and/or are too proud to carry or wear reading glasses or, heaven forbid, bifocals to the barn, have great difficulty deciphering "Is that 1 cc per mL or 2?". Reading beyond the dose to the fine print is out of the question. Warnings on the package inserts for the avermectin products, Eqvalan® and Quest, caution the user to "Wash hands after use." "Dispose of by burial or incineration." "Avoid direct contact with skin and eyes." These are rarely read or followed. Veterinarians should provide readable instructions for every medicine dispensed.
The barn is not a suitable storage area for medications, unless medications are protected from freezing and/or overheating.
Medications should be stored according to the manufacturer's recommendations. Some will require refrigeration but are not able to withstand freezing. The barn window or bright shelf in the tack room may not be a suitable storage location for medications that may be sensitive to light.
Plumb DC. Veterinary Drug Handbook 4th ed. Iowa State Press, 2002.
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