Pets can only be treated with pet-only medicines
As a vet, one of my key powers is being able to prescribe and dispense medication. I'm allowed to do this under Irish law. Without being able to do this, I would not be able to treat the sick animals that I see every day.
Animal medicines are strictly regulated, and so they should be: if the wrong medicines are given to the wrong animals, there can be serious adverse consequences. And important issues like antibiotic resistance can only be tackled by careful, well-informed use of the right antibiotic for the right situation.
Animal medicines have not always been so tightly controlled: during my career, over the past twenty five years, there has been a significant increase in restrictions on how vets are allowed to provide treatment for animals.
Back in the 1980's, vets were more-or-less allowed to buy and sell any medications on the market for the animals under their care. We could order the same range of drugs as human doctors, using the same wholesalers who supply pharmacies. The signature of a vet was the same as the signature of a doctor in this regard. This gave vets (and pet owners) a great deal of flexibility. If a drug was available for humans, we could search through the literature, look for examples where it had been used in animals, work out a dose, then prescribe the drug for our patients.
This all changed in the 1990's, with increasing regulation of what vets are allowed to do. It was recognised that the ideal medicines for animals were those that had been individually assessed for safety and efficacy for a specific use in a particular type of animal. The older idea that a drug would "probably work well enough" was no longer acceptable.
The fact is that individual animal species have physiological differences from humans and from each other. These differences can have a significant effect on the way the animal responds when it is treated. New laws were brought in, at a European level, to control drugs more tightly, to reduce the risk of harm being caused by inappropriate medications being given to animals.
Under the new system, manufacturers of veterinary medicines have to apply for specific licences which prove safety, quality and efficacy for their products when used in specific situations. Vets are no longer allowed to use the human equivalent drug if there is a veterinary version.
These changes were disliked by vets (and by pet owners) at first: the specific veterinary versions of many drugs were often more expensive than the human generic versions. The human drugs are produced in such high volumes that significant cost savings are possible during manufacture and distribution. The restriction of vets to animal-only products meant that pet owners had to start paying more money for medicines when their pets fell ill.
On first impressions, this seems unfair: surely if the label on a human drug shows that it has identical ingredients to the label on the animal drug, it should be just as effective, and if it's cheaper, surely the owner should be able to avail of that saving?
This is where the science comes in: animal medicines containing the same active ingredient as human medicines may appear almost identical, but they are often formulated differently. For example, for orally administered products like tablets and capsules, the formulation needs to ensure that the medicine is properly absorbed through the digestive system. There's a great deal of difference in how the digestive processes works between animal species, as well as between animals and people. The stomach has different levels of acidity and there are different enzymes in the intestines. Using a medicine which is not authorized for animals increases the risk of treatment failure or harm to the treated animal.
The new laws meant that it became an offence for vets to prescribe or dispense human medicines when there are licensed veterinary products. Vets can be fined and disciplined for doing so. This legislation protects animals, but there's a financial cost to the owner for this extra care.
The law does recognise that there are circumstances where the benefits of treatment of animals with "unauthorised medicines" outweigh the risks. This applies particularly where there are no veterinary authorised medicines for a rare condition. As a result, legislators have created a 'prescribing cascade', commonly referred to as 'the cascade', which allows vets to occasionally use particular products that are not specifically licensed for the animal they are treating. This exemption exists to help animal health and welfare in situations where there is no other alternative. In such situations, vets need to justify why they are using the unauthorised product, using facts that can be audited by inspectors if needed.
Cost cannot be used to justify using unauthorised drugs, which can be frustrating: a vet-licensed drug may cost twice as much as the human-licensed one, even though they may outwardly appear very similar. Vets are not allowed to use the cheap human version to save owners money.
The animal medicine laws are strict for a good reason: they prevent animals from suffering.