Rx: Responsible Drug Use
Tranquilizers can calm a nervous, first-time dam and allow her to accept her foal; anti-inflammatory drugs may allow a mildly arthritic horse to continue safely in a handicapped riding program; antibiotics can be life--and career--saving to a racehorse with pneumonia. At some time, medications could be an important part of the equation in your horse's health, which starts with a relationship with your veterinarian.
The Veterinary Connection
The telephone calls (and now e-mail) are incoming at least five or six times every week--"My horse has mange and the stuff that my veterinarian gave me isn't working. What should I use?" "A yearling of mine has chronic diarrhea and I've tried everything, but nothing has worked. What do you suggest I try next?" And even international calls: "My horse has white muscle disease, what should I give him ... there have only been three cases in my country."
Veterinarians (or physicians, dentists, etc.) cannot diagnose a condition or prescribe treatment over the telephone without direct knowledge of the animal. Think of it this way...can you imagine calling up a cardiologist and saying (if you could even directly speak to him/her) "Gee, I really don't agree with my physician about what is wrong with my fluttering heart. This is what it feels like, and this is the medication I am on--what other drugs could I try?" No upstanding physician would attempt to answer that question without directly examining you and perhaps conferring with your original physician with your permission. Why do animal owners expect veterinarians to do things differently?
There is, however, a big difference if an animal owner requests information regarding skin diseases of horses, causes of chronic diarrhea, or inquires about vitamin E/selenium deficiency. This information is readily available on the Web, in text books, and in magazine articles, and it is not in any way meant to encourage horse owners to diagnose or treat their horses on their own. But when owners are asking for information on treatment of a specific condition in a particular animal, the veterinary-client-patient relationship (VCPR) comes into play (see sidebar below). This is a basic, fundamental concept in veterinary medicine. For the health of your animal, establish a working relationship with a veterinarian before you need his or her services. When you get to know your veterinarian (and vice versa) and that colic occurs at 2 a.m., you can call a professional who already is familiar with your horse and your facilities, you can give a description of the problem, and get some advice on what to do until he arrives.
A pet peeve of one Montana veterinarian is to arrive at a farm with a horse that has had colic for several hours, only to find the animal "floating" on Banamine when it really should have had immediate veterinary attention. One owner called in the middle of the night with a horse which had colic for the past nine hours. Upon rigorous questioning, the owner reluctantly admitted that he administered three full doses of Banamine because he noticed the horse was uncomfortable. (The usual dose of Banamine is one dose every 24 hours, not one dose every three hours.) The last dose was not successful in alleviating the pain, so only then was the vet called. When the veterinarian arrived and examined the animal, it had a severe impaction colic and was seriously dehydrated. Self-diagnosis and treatment are not the best courses of action!
Prescribing Medication Is The Role Of The Veterinarian
Owners should be educated about any medications that are prescribed for their animal, or are obtained over-the-counter, such as dewormers. If you have questions, ask your veterinarian--if it still isn't clear, ask for more information. Sometimes it is best to write down the directions.
The prominent instruction "READ THE LABEL" is there for a reason, since the printed material on the box, or in the package insert, contains valuable information. Other sources of information on veterinary drugs include Veterinary Pharmaceuticals and Biologicals, which is equivalent to the Physician's Desk Reference for humans, as well as the Web pages maintained by veterinary pharmaceutical companies.
Read The Label
Reading and understanding the drug label are important prior to administering a drug. That tiny piece of paper included in the box of tablets or glued to the bottle's side, with bifocal-inducing tiny print, has a world of information. So, let's take a walk through the standard sections of most prescription drug inserts.
What's in a name? The trade name usually is listed first. Banamine is the registered trade name for the drug flunixin meglumine. When a drug is first introduced into the market, the parent company holds the patent for the drug and no generic alternatives can be produced for a period of time. When the patent expires, comparable drugs made by several manufacturers can be marketed under different names. Sometimes drugs are referred to by common names, such as "Bute" being phenylbutazone. It is best to know the generic name of the drug that is being used on your horse to eliminate any confusion among the multitude of brand names for the same drug.
OTC vs Rx drugs Over-the-counter (OTC) drugs can be purchased without a prescription, and can be classified that way for several reasons. The drug must be relatively safe to use without the supervision of a doctor and have clearly written directions for use. Dewormers, certain antibiotics, and topical medications for wounds are some examples. (See article on Administering Medications in The Horse of June 1998, page 43.) In recent years, several human prescription drugs became available OTC, such as Motrin and Zantac (anti-ulcer medication); however, they are available in lower concentrations than the prescription drugs.
The symbol "Rx" on a drug insert next to the name indicates it is available only by prescription from your veterinarian because professional knowledge is needed about the animal and the disease condition prior to drug administration. For example, the antibiotic gentamycin is commonly used in horses, but can cause kidney damage if overdosed or used for an extended period of time. It is neither possible nor wise to have cardiac or pulmonary drugs available over-the-counter, since precise diagnosis and choice of drug are critical to a positive outcome.
Other drugs which are available by prescription only include tranquilizers, depressants, stimulants, and anabolic steroids. Drugs that leave tissue residues are also Rx drugs since improper administration could cause the drug to enter into the food chain via animals used for food purposes. A prescription drug label will have a statement such as: "Caution: Federal (USA) law restricts this drug to use by or on the order of a licensed veterinarian." A VCPR must be in place for a veterinarian to prescribe Rx drugs for a client's horse.
This was not an adverse drug reaction. The drug elicited a response by the cardiovascular system that caused a severe decrease in blood pressure. The drug was dispensed for use in normal, but nervous, horses, but not for an agitated horse with a serious wound. Had the horse owner made a quick telephone call to her vet, or twitched the horse and received some reinforcements to control the animal while applying an appropriate pressure bandage, there would have been a simple wound repair waiting for the veterinarian, instead of a horse in shock with a bleeding wound. The veterinarian promptly came and the horse is now just as feisty as before the incident. Because this drug is a potent tranquilizer and has side effects that cannot be easily explained on a label for lay persons, it is available by prescription only, and must be used within a VCPR.
Indications The drug's primary actions and the species it is approved for are listed here.
Description, Activity/Actions. These sections of the package insert describe what is contained in the drug, including additives, preservatives, and the drug's main purpose in life. Flunixin meglumine "is a potent, non-narcotic, non-steroidal, analgesic agent with anti-inflammatory and anti-pyretic activity." For antibiotics, "Actions" will describe the spectrum of infectious agents it has been shown to be effective against, and where in the body the drug maintains its highest concentrations. Sometimes this is pretty technical stuff!
Toxicity Information about toxic reactions to drugs during testing is included here. For example, in addition to kidney problems with high or extended doses of the antibiotic gentamycin, impairment of equilibrium also was noted. This information can be especially important if the calculated drug dosage is off by one decimal point--giving 10 cc of a drug instead of 1.0 cc!
Pharmacokinetics The activity of drugs in the body from time of administration through distribution in the body through metabolism through excretion--and everything that happens in between--is known as pharmacokinetics. Certain antibiotics are better for killing bacteria in bone than in the brain, for example, mainly because the drug can penetrate specific tissues better. Rifampin and erythromycin are commonly used together to fight Rhodococcus equi infections primarily because they have a synergistic, or complementary, effect and thus are more effective at penetrating the R. equi abscesses in the lungs than certain other antibiotics.
Dosage Drug dosage is not always black and white, primarily because horses do not read the drug inserts! Each horse is an individual, and the dose of a tranquilizer that works in a 1,000-pound Quarter Horse might have less (or more!) effect on a 1,000-pound Belgian youngster. A veterinarian factors in many variables when deciding upon a dosage for an individual horse, such as the drug itself with its known actions and side effects, the horse's age, general health, temperament (especially with tranquilizers and anesthetics), concurrent medications being given, and even breed. Because of this, owners should not take it upon themselves to adjust a medication dosage based on the latest news article or information gained from the Web.
Administration An excellent discussion regarding routes of administration can be found in the June 1998 issue of The Horse (pages 43-49). Another lesson learned the hard way: one horse owner assumed that phenylbutazone could be used IM. As soon as she injected the drug into the neck, the horse literally "jumped off the needle" in pain. The veterinarian was called since the horse could no longer be touched on that side of the neck. Skin and muscle tissue sloughed off the area of injection. Injectable bute is only for IV use, which is stated on the label. As is well stated in Dr. Mike Ball's article of June 1998, IV administration should only be attempted by people who have had special training, due to many potential complications.
Another factor to consider when administering an injectable drug: make absolutely sure about the amount administered, because once the syringe plunger is depressed, you can't take the drug back out of the horse!
Contraindications, Precautions, Cautions, and Warnings This group of headings always should be read and heeded. Information might include animals for which the drug should not be used (stallions or broodmares, horses with shock or certain organ abnormalities, such as kidney failure); drugs which should not be administered concurrently; specific emphasis on how the drug should be administered, etc. Even if the warning is not printed in black and white on the label, always keep animal drugs away from children!
Storage So what? You just keep medicine in the tack trunk all year long anyway, don't you? Many drugs need to be kept away from light so they retain potency. The temperatures at which medication needs to be kept also are important. All of these cautions are listed under the "Storage" heading. Procaine penicillin needs to be refrigerated, not kept on the dashboard of the truck in July, which inevitably results in "Dashboard Death." Not only can the effectiveness of the drug be decreased, but harmful chemical reactions can occur when drugs are not properly stored, such as crystal or precipitate formation.
Sometimes there is other, more detailed information on the label, sometimes less, depending upon the drug and whether it is OTC or prescription. The above details of drug inserts will help owners understand the medication's actions better.
Don't Extrapolate Between Species
Just as it is not prudent to assume the same mg/lb dosage of drug can be used in both adult horses and newborn foals, or between a healthy horse and a 30-year-old retired broodmare, neither is it suitable to extrapolate use of drugs between species. Many drugs that can be used in horses are not approved for use in food producing animals. Additionally, drug dosages for a 1,000-pound horse might be vastly different than for a 1,000-pound cow. For example, the same dose of xylazine for sedating a 1,000-pound horse could easily knock out a similar-sized bovine--and if that animal is in a chute, it might die from not being able to breathe. Xylazine is not labeled for use in food animals and must only be administered under the direction of a veterinarian.
The fact of life is that an adverse reaction to a drug can occur even in an absolutely healthy horse given the exact dose, by the appropriate method, out of a new bottle, by a DVM, PhD, Board Certified-in-Everything veterinarian. The way to reduce the risk of this happening is by consulting a veterinarian regarding the use of drugs, asking questions, and reporting any adverse reactions shown by your horse. Do not extrapolate drug dosages from other large animals. Do not use drugs in an extralabel manner on your own. Do not change the prescribed dose without speaking to your veterinarian. And never mix drugs or vaccines in the same syringe!
Veterinary Pharmaceuticals and Biologicals, 10th edition. (1997/1998) Veterinary Medicine Publishing Group, Lenexa, Kan.
Hoopes, KH, Thwaits, RN. Principles of Veterinary Science. Williams & Wilkins, Baltimore, 1997.
ASPCA/National Animal Poison Control Center Hotline
Telephone consultations are available to both veterinarians and animal owners in cases of suspected poisonings. There is a charge per case, which is paid via credit card. Callers should be prepared to supply information such as the suspected substance, details of exposure, and clinical symptoms.
Drugs In Show Horses
The American Horse Shows Association (AHSA) has strict guidelines for the legal use of certain NSAIDs. However, there is concern about horses which have been administered three, or even more, different NSAIDs concurrently.
Let's think about this...if you have a sore back, do you go home and take a full dose of acetominophen, and aspirin, and ibuprofen, and ketoprofen? (Sorry, there is no bute or flunixin meglumine labeled for human use.) Likely not. If the pain were that severe, hopefully you would call a physician for advice.
"Administering multiple NSAIDs to one horse can cause serious problems, especially over the long term," stated Richard Smith, RPh, DVM of Prescott, Ariz. As both a registered pharmacist and veterinarian, Smith commented, "Not only is there danger of gastrointestinal problems such as ulceration and diarrhea, but also the significant potential for kidney, liver, and other organ damage in animals." Mixing multiple drugs together also has the added risk of adverse drug interactions, which can be even more harmful to the body.
Besides the AHSA penalties for illegal drug use in show horses and the potential serious side effects, why would any reputable owner or trainer administer four or five NSAIDs to a horse for competition?
About the Author
Roberta Dwyer, DVM, MS, Dipl. ACVPM, is a professor within the University of Kentucky's Maxwell H. Gluck Equine Research Center and editor of Equine Disease Quarterly.
POLL: Horses Living With Livestock