The cascade is a risk based decision tree. The steps, in descending order of suitability, are:

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

If there is no such product that is clinically suitable, either:

• A human medicine authorised in the UK, or

• A veterinary medicine not authorised in the UK, but authorised 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 authorised in a food producing species. If there is no such product that is suitable:

• A medicine prescribed by the vet responsible for treating the animal and prepared especially on this occasion (known as an extemporaneous preparation) by a vet, a pharmacist or a person holding an appropriate manufacturer’s authorisation (ManSA). In exceptional circumstances, where there is no suitable veterinary medicine available either as an authorised product or under the cascade, a vet may treat an animal with a medicine authorised in a country outside of the EU via the Special Import Scheme.