Compounding drugs may allow you to get a medicine in a form you prefer, such as a liquid over powder.

Compounding is the practice of hand-mixing drugs to meet a special need for a different dosage or different ingredients, including the inactive bases, than is available from a pharmaceutical company. Compounding may also be allowed if a horse needs a drug that no longer is being manufactured, as long as it wasn’t withdrawn from the market for safety reasons, such as the issues with pergolide for human use but without safety concerns for horses (see June 2007).

There are compounded flavored phenylbutazones, anti-ulcer medications and antihistamines, liquid formulas for foals, and a variety of injectables, including joint treatments, hormones, performance concoctions and more. There’s even a company offering an apple-flavored reserpine, the long-acting tranquilizer.

While compounded drugs are supposed to be made from FDA-approved active ingredients, the final product is not an FDA-approved drug. Compounded drugs in their final form don’t have to be tested for potency, safety, sterility or shelf life.

POTENCY. Even if the compounded product contains the stated amount of active substance, there’s still no guarantee it’s as potent as a drug-company product. If bulk drug is used to make the product (only allowed for drugs no longer on the market), the shelf life of the bulk drug is often much shorter than in a finished product.

Encapsulation and protective coatings on pills greatly prolong the active life of the drug. Bulk powders may have been stored beyond their expiration date, or under conditions that frequently expose them to heat, light, air/moisture and lead to early degradation of the drug.

Compounded drugs made from a commercially available pill or capsule have a more reliable starting potency, but the processing required to make the compounded product immediately destroys that advantage for the finished product.

SAFETY. Compounded drugs are made either from drugs that have already completed the FDA-approval process, or vets may use their experience and judgment in prescribing a medication that has not been officially approved for the species. There are other considerations, though.

A compounded formula may be absorbed at a different rate or have irritating effects on the intestinal tract, vein or muscles. The pH of the product or the inactive ingredients could either increase or decrease the bioavailability of the product, leading to either over or underdosing compared to a tested product. In addition, even the inactive ingredients in drug company products must be at least USP grade.

STERILITY. Drug manufacturers are required by law to routinely test their injectable and oral medications for bacterial contamination and to manufacture them under carefully specific clean or sterile conditions. There’s no similar law for compounded drugs.

SHELF LIFE. This is where you can really get into trouble. Pergolide again is a good example, but the same applies to other drugs. Bulk pergolide powder has a shelf life of six months compared to two years or more for the pills that are no longer available. If your compounder’s pergolide is older than six months from the date the powder was made, you may be getting a drug that is less potent.

Formulations
Drugs may be made into:

Capsules: These are powder loaded into individual capsules.

Loose powder: Allows you to measure a dosage by a convenient measure like a teaspoon. True shelf life of loose powders that are opened once or twice a day is unknown.

Liquids: Depends upon whether it’s water- or oil-based. Be sure you ask.

Flavored chewable treats: These are a complete unknown in terms of how well the medication is absorbed.

Bottom Line
One reason compounded drugs are so inexpensive is that the pharmacies do not have to jump through the same quality-control hoops as drug manufacturers do. If you need or want to use a compounded product, start by asking if the pharmacy has an independent analysis on their finished product, and if they have conducted shelf-life studies. Most won’t, but it never hurts to ask, and it clearly sends the message that you know how to ask the hard questions.

Don’t rely on statements like "We’ve been making this for 20 years" or "Thousands of vets use our products." Get the most stable form of the drug available, preferably capsules, and ask about ideal storage conditions.

Finally, if your horse doesn’t respond to the product as he should, switch to a more stable formulation or another pharmacy before giving up on the drug your vet recommended.