By Karen Rosenthal, DVM, MS
One of the many mysteries in medicine for ferret owners is how veterinarians determine a dose of a drug for their pet. Some people may believe that doses are all based on hard scientific facts developed after extensive research but, unfortunately, many of our doses for ferrets are based on the doses that seem to work in dogs, cats and other animals.
The determination of a correct dose is developed either by:
- Research studies in ferrets (very uncommon)
- Research studies in closely related species (also uncommon)
- Research studies in distantly related species (more common)
- This drug dose has worked for 20 years, let’s use it (most common)
The two most important considerations when using a medication in ferrets are — is this drug safe and is it effective. Of those two concerns, safety is the most important aspect of drug dosing. The goal is to have a high enough blood concentration of the drug for a long enough time such that the drug is effective and side effects are minimal.
Based on this goal, some drugs can have high enough blood concentrations for many hours, which allows us to prescribe the drug in a once a day or even every other day manner. Some drugs are metabolized and eliminated through the liver or kidneys so quickly that the concentration needs to be replenished every few hours, which translates into dosing three to four times a day.
Knowing how a drug is metabolized or eliminated is extremely important in tailoring the drug dose for a particular ferret. For example, if a ferret with hepatitis needs to be sedated with a drug that is metabolized by the liver, only half the normal dose will be given to the ferret as that drug will remain in the ferret’s system much longer than normally would be expected than in a ferret with a properly functioning liver.
Also as confusing, is the volume of medication that is given. It is important not to confuse volume with dose. Dose refers to the milligrams of drug that is delivered into your ferret, and that depends on the amount of the drug that needs to be circulating in your ferret’s bloodstream. Volume depends on the concentration of the drug in the form in which it is administered. A very dilute concentration means a larger volume (i.e., bigger pill or more liquid) is given to your ferret versus a very concentrated formulation, which allows a smaller amount.
For example, let’s assume your ferret needs 1 milligram (mg) of prednisone orally. If the concentration of the drug formulation is 10 mg of prednisone per 1 milliliter (ml) of liquid, then your ferret will need only 0.10 ml of medication. But if the concentration of the drug formulation is 1 mg of prednisone per 1 ml of liquid, then your ferret will need 1.0 ml of medication to get the same dose of drug (1 mg). So, if you have always given 1 ml of a liquid prednisone medication to your ferret and now your veterinarian tells you to give only 0.1 ml, the dose may not have changed, but your veterinarian is now using a more concentrated form of medication even though your ferret is getting the same dose of prednisone.
Finally, why are there different liquid concentrations with the same drug? This is all dependent on the manufacturer of the medication. Different manufacturers produce different concentrations. And if your veterinarian or a pharmacist needs to make up the medication specifically for your ferret (called “compounding”), he or she can make the medication into their own specialty concentration that best suits your ferret’s needs.