The Cascade (“Off-label drugs”)

The cascade is a set of legislation that vets are legally obliged to follow. It is made to ensure that vets use drugs that are licensed for the species of animal and the indication for which they are prescribed whenever possible, while providing the flexibility to allow use of drugs that are not licensed when no licensed drugs are available. This is to ensure safety for the animal, the owner and vet administering the drug and for the environment, while at the same time allowing sick animals to be treated in the most appropriate way when they become ill.

Licensed drugs will have undergone rigorous tests to ensure that they are safe and effective in treating specific diseases in specific species. Unfortunately there are relatively few drugs specifically licensed for horses, which means that we need to use other drugs licensed in other species or people.

The cascade is as follows:

Veterinary surgeons must use medication licensed for the species (e.g. horse or donkey) and indication (i.e. illness or medical condition) for which they are prescribed. If no such medication is available the cascade is followed (this is called “off-label use”):

1. Use another veterinary medicine licensed for another species, or one that is licensed for another indication in the same species where appropriate
2. Use a medicine authorised in the UK for human use
3. A medicine can be made up at the time on a one-off basis by a veterinary surgeon or a properly authorised person.
4. If no appropriate medication exists that is authorised in the UK, it is possible to use a medication authorised in a different country if a special import licence has been issued by the Veterinary Medicines Directorate.

Use of “off-label” drugs:

The use of off label drugs may be necessary when licensed medicines are not available, but there are certain risks involved. Drugs can be metabolised differently in different species, so although it may be safe in one species it can be harmful in another, or the dose required may be different. The same goes for use of human drugs in animals. It is down to the prescribing veterinary surgeon to use their clinical knowledge and experience to weigh up the risk versus the benefit of the treatment in each case. They must inform the owner that an off licence medication is being used and will ask the owner to sign a form agreeing to this use. In the majority of cases the drug will have been used previously and will have shown to be safe and effective in a clinical setting, even though it has not been subjected to the licensing protocols.

It is very expensive and labour intensive to get a drug tested and approved for each species and indication, so unless a large market exists for the particular drug it may not become licensed. It is however, important to use the licensed drugs whenever possible, as this is not only the best way to ensure safe and effective treatment, but also provide funds to further the research and allow more drugs to become tested and licensed for animal use.