compounded drugs in equine practice

COMPOUNDED DRUGS IN EQUINE PRACTICE

William E. Jones, DVM, PhD

The practice of equine medicine becomes more sophisticated every day. There is a knowledge explosion in mat- ters pertaining to equine medicine, as therapies for human diseases are tried in horses and found to be successful. However, the armamentarium of the equine practitioner is sadly deficient, compared to that of the human physi- cian. A relatively few FDA-approved drugs are labeled for use in horses.

"The dilemma of equine veterinary medicine is that practitioners find themselves attending to conditions for which there are little clinical data to support therapeutic choices," said Dr. Joseph Bertone, speaking at the Con-

vention of the American Association of Equine Practitioners (AAEP), in Phoe- nix, AZ. "In these situations, equine veterinarians often use compounded medications. ''1

Dr. Bertone took the position that the veterinarians cannot depend on current regulatory actions to assure the quality of compounded drugs for veterinary use. He advised that veterinarians are ultimately responsible for the quality, strength, purity and stability of the compounded drugs purchased from a pharmacy. Pharmacy practice is regu- lated for the most part by the state pharmacy boards, but Dr. Bertone was skeptical as to the assurance this brings to quality of veterinary compounds.

In order to show due diligence in selecting a compounding pharmacy, equine practitioners should consider the following:

• Compounded medica t ions should be prepared in a state-licensed facility and certified clean room.

• Compounding pharmacies should have an experienced staff of pharmacists and technicians dedicated exclusively to compounding.

• Injections should undergo quality assurance and quality control for sterility.

• Compounding pharmacies should maintain an inventory of USP/ NF-grade prescription chemicals.

• Compounding pharmacies should adhere to USP guidelines of good compounding practices.

• Compounding pharmacis ts should routinely attend national, state and regional veterinary meetings to explore the needs of veterinarians, to support the veterinary community, and to keep abreast of new developments

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and treatments. Estimates are that 40 to 80% of the

drugs used in the typical equine practice are compounded drugs. Whatever the percentage of compounded drugs used in equine practice, it is alarming that so little reference is made in the literature to common compounds. Equine practitioners have little information available to them as tO what other practitioners prescribe or use.

A limited telephone survey of pharmacies filling prescriptions from equine practitioners in their own state and out of state revealed that a compound for equine protozoal myeloen- cephalitis (EPM) was the most requested compound. This was generally pyrimethamine, one mg/kg orally, once daily, in combination with a sulfona- mide antimicrobial (such as sulfadiaz- ine) with or without trimethoprim, administered orally, once or twice daily, 20 to 30 mg/kg. Sometimes vitamin E was included, and often folic acid or brewers yeast was requested to help offset the anemia which is often caused

by pyrimethamine. (See page 172 for current recommendations on EPM treatment,)

The second most common equine prescription request was for drugs which are no longer available commercially, such as dipyrone, combiotic, and some steroid injections. Estrone and testosterone are high on the list. A very common prescription is for injectable drugs not available commercially in the required concentration. Sometimes generic components of popular drugs, such as ivermectin, are put into special formulations to make up a more palat- able paste for horses- - such as an apple flavor. Combinations of NSAIDs in various formulations for specific cases are popular. Ophthalmic prescriptions are common for drug concentrations or forms not commercially available.

Hormones for injection include estrone, testosterone and progesterone. Estrone is being used for exercise-in- duced pulmonary hemorrhage (EIPH). Testosterone is used in horses to im- prove weight gain, strength and perfor-

Volume 19, Number 3, 1999 155

TALKING IT OVER

mance. Perhaps the most widespread use of progesterone is to control estrus cycles. Prednisone injection (crystal- line prednisone suspension) is used for treatment of inflammatory conditions of the skin and joint and for supportive care during periods of stress.

The veterinarian writing a prescription for a compound he/she has not previously requested should consult the pharmacist as to compatibilities of the ingredients, stability and other fac- tors which might impact the quality, effectiveness and safety of the drug. The prescription is a legal document directing the pharmacist to prepare the prescribed medicine, affix the direc- tions, and sell the preparation to the client or patient. The writer of the prescription is held responsible for its ac- curacy.

Traditionally veterinarians have done more dispensing than prescribing, but our changing legal environment and the unavailability of many useful drugs is causing a shift to more prescription writing. In 1955 Knapp 2 enu- merated the reasons why veterinarians should become adept at prescription writing and employ the services of a registered pharmacist. These reasons still apply today.

1. The veterinarian can charge just about the same fee as when drugs are dispensed; payment for services and knowledge rather than just payment of the remedy should receive higher prior- ity.

2. Writing a prescription elimi- nates the cost of the dispensed item so that subtraction from the fee is obviated.

3. Prescribing provides the prac- ticing veterinarian with a supply of pharmaceuticals that might not always be available on the shelves of the clinic.

4. Prescriptio n writing reduces the investment tied up in drug inventory when one dispenses drugs.

5. If a client does not pay the bill, cost of the medicines dispensed are not lost.

6. Prescribing can bring about im- proved cooperation between the pharmaceutical and veterinary medical professions.

7. The client is frequently more inclined to pay for two smaller fees

than one large fee. 8. Prescription writing provides a

means for learning, including an appre- ciation of drugs and their actions, indi- cations, and dosages; individuals adept in prescription writing usually have

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more detailed information at their com- mand than those who are not.

It should be pointed out that it is legal for a practitioner to purchase a supply of compounded medications to hold in inventory to be administered by the veterinarian in the treatment of pa- tients.

The prescription should have seven parts to be complete. 3

1. The date of writing the prescription.

2. The identity and address of owner and patient.

3. The superscription, Rx, is an abbreviation of the Latin word recipe meaning "take thou of."

4. The inscription lists the names and amounts of drugs to be incorpo- rated in the prescription. Names of the drugs should be written in English and the total amounts required should be written in the metric system, which is preferred and official in the USP-NE

5. The subscription gives the instructions to the pharmacist. These in-

structi0ns may be entirely in English or with Latin abbreviations.

6. The signa (Sig. or S.) consists of instructions for administration of the medicine, which the pharmacist types on the label.

7. The signature of the practitioner must appear on written prescriptions to make it a legal document, but oral prescription orders via fax or phone are permissible with the exception of certain scheduled drugs.

Incompatibilities between two or more drugs in a compound, or in a patient, can reduce drug safety or efficacy. Three types of incompatibility may be encountered in practice: 4 therapeutic, chemical, or pharmaceutical. Knowledge of these is necessary for the veterinarian to avoid unnecessary problems with therapy and to be able to antagonize certain drug effects.

According to Booth, a "Therapeu- tic incompatibilities occur as a result of antagonistic pharmacological actions in the patient or interference with drug

absorption following administration; e.g., a therapeutic incompatibility will arise if you simultaneously administer physostigmine and atropine in the eye. Physostigmine constricts the pupil, whereas atropine dilates it. Chemical incompatibilities will manifest themselves in a number of ways (precipita- tion, change in color, evolution of gas, gelatinization, inactivation without any visible change). This may be the result of the drugs undergoing a chemical reaction, pH changes in the dosage forms, interactions with preservatives or solvents in the dosage form, and combination of divalent cations with components of the mixture. Pharma- ceutical incompatibilities are usually of a physical nature, e.g., incomplete solutions resulting from low solubility of drug in a given solvent, immiscibil- ity of liquids mixed together, and pre- cipitation. One can avoid these problems by thoroughly understanding the actions of drugs used in therapy, using

Continued on page 205

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Continued from page 158

the services of a pharmacist, refraining from mixing different medicaments in the same syringe prior to administration, and being parsimonious in use of drugs."

In the current FDA environment we live in here in the United States, proof of efficacy and safety is a prime consideration when a drug is administered to a patient. The original Food and Drug legislation did not seriously consider the needs of the veterinary profes- sion and shoehorned requirement for veterinarians into a common law for use of drugs by all health care profes- sionals. Eventually the veterinary pro- fession gained passage of a new law which recognized the dearth of drugs labeled for veterinary use in the various species treated. Now extra-label use is a legally and accepted procedure in equine practice, and an important question in everyone's mind is how do I know the prescribed drug is efficacious and safe.

Sometimes there are preliminary trials which show a drug to be promis-

ing for a particular equine condition, but there is never the kind of proof we have become accustomed to with FDA ap- proval. As a result each practitioner is faced with determining his/her own level of comfort with the kind of "proof ' which is available for any extra-label drug use. This is also true of most compounds. It generally comes down to ask- ing advice from other equine practitioners who have tried the compound or extra-label use of a drug before. Essen- tially, the question of safety and efficacy regarding extra label use and compounded prescriptions is based on the clinical observations and experience of practitioners, as has occurred throughout the history of medical advancement.

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R E F E R E N C E S

1. Bertone J J: Good clinical practice and compounded drugs. AAEP Proc 1997;43:178-181.

2. Knapp WA: Southeast Vet 3. Booth NH, McDonald LE:

Veterinary pharmacology and therapeutics. Iowa State University Press.

4. Davis LE: In: W Guin (ed) Veterinary Values. New York: Ag Resources.

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Volume 19, Number 3, 1999 205

compounded drugs in equine practice

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