When I started practicing exotic animal medicine, more than 2 decades ago, practitioners in the Netherlands generally used three different drug: doxycycline, prednisolone and euthanasia solution.

The most commonly used antibiotic currently is enrofloxacin. The question arises, however, if this antibiotic should be chosen over any other. As mentioned during the lecture on “Advanced therapeutics in rabbits”, fluoroquinolones have been placed by the World Health Organisation (WHO) on the list of critically important antimicrobials, thereby restricting its use to specific circumstances where no other antibiotics can be employed anymore. Antibiotics such as doxycycline and trimethoprim/sulfamethoxazole, however, are still excellent choices for treating bacterial infections in companion mammals. The most commonly used antifungal drug in companion mammals is itraconazole, although others may be just as effective. The most commonly used antiparasitic drug used in companion mammals is fenbendazole. Not only is this used for endoparasite infections, but it is also the most common treatment option for E. cuniculi infections in rabbits. For the ectoparasitic infections. Ivermectin and selamectin are most commonly used. These drugs have proven to be very effective, although higher dosages compared to the more common companion animals may be needed. The drugs used for other conditions (e.g., cardiac disease; gastrointestinal disease; endocrine disease; ophthalmological disease; etc.) are most commonly based on knowledge obtained from dog and cat medicine.

Based on What Criteria Should Any Drug Be Chosen?

In 1996, the first edition of the extremely practical “exotic animal formulary” from Carpenter came on the market. This has revolutionized the use of drugs in exotic animals and at the time of writing the 4th edition has become the standard in practice. Aside from this formulary, the BSAVA has an “Exotic Pets” (9th edition of their small animal formulary. Both formularies should be considered complementary to each other as their approach is different. The BSAVA formulary has the drug as main search topic and then provides the dosages for the different species, while the “Carpenter” formulary has sections divided by species. What these formularies have in common though is that they demonstrate the huge amount of drugs that can be used in companion mammals, and other exotic animal species. Unfortunately, this comes with a price as well. So many different drugs are mentioned and so many different dosages are given that a strategy needs to be followed to select the appropriate drug and dose.

For exotic companion mammals, not many drugs have been registered for use in these species. The selection of a drug of first choice should therefore be chosen by using the Cascade. The British government has defined the Cascade as a “risk based decision tree that allows you to use your clinical judgement to treat an animal under your care by deciding which product to use when there is no authorized veterinary medicine available”. The steps that have to be followed (in descending order of suitability) are:

• A veterinary medicine authorized in the UK for use in another animal species, or for a different condition in the same species

If there is no such product, either:

• A medicine authorized in the UK for human use, or
• A veterinary medicine not authorized in the UK, but authorized in another member state for use in any animal species in accordance with the Special Import Scheme; in the case of a food-producing animal the medicine must be authorized in a food-producing species
• A medicine prescribed by the veterinarian responsible for treating the animal and prepared especially on this occasion (known as an extemporaneous preparation or special) by a veterinarian, a pharmacist or a person holding an appropriate manufacturer’s authorization (so called specials manufacturers)
• In exceptional circumstances, medicines may be imported from outside Europe via the Special Import Scheme

With regard to the selection of antibiotics, however, the cascade is overruled by the guidelines of the WHO.

When these guidelines have been followed there are still selections to be made. These are based on available evidence and (pharmacokinetic and pharmacodynamic) studies that have been performed with the selected drugs. When looking at the formularies, all drugs dosages are referenced. With the aid of these references, information can be obtained where the dosage is based on (personal experience, or performed studies).

After having followed these steps, the most appropriate drug may be chosen.