The Cascade: Prescribing unauthorised medicines

Guidance for prescribing vets on the use of the Cascade.

If there is no suitable veterinary medicine authorised in the UK to treat a condition in a particular species, you can treat an animal under your care in accordance with the Cascade.

The Cascade is 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 authorised veterinary medicine available in the UK. As part of the Royal College of Veterinary Surgeons (RCVS) Code of Professional Conduct for Veterinary Surgeons, you must obtain the owner’s consent for their animal to be treated under the Cascade.

You should balance the benefits against the risks of not following the clinical particulars on the Summary of Product Characteristics (SPC) and take responsibility for your decision. Risks could include those to:

  • the animal
  • the owner
  • the person administering the medicine
  • consumers of food which may contain residues of the veterinary medicine
  • the environment
  • wider public health, for example, increased selection for antimicrobial resistance

If you ignore the advice and warnings in the SPC, you may be open to litigation if something goes wrong with the treatment, as the advice and warnings given are there for good reason and based on assessed data.

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 available, either:

  • a medicine authorised in the UK for human use, 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 available:

  • a medicine prescribed by the vet responsible for treating the animal and prepared especially on this occasion (known as an extemporaneous preparation or special) by a vet, a pharmacist or a person holding an appropriate manufacturer’s authorisation (so called specials manufacturers)

  • in exceptional circumstances, medicines may be imported from outside Europe via the Special Import Scheme

You or the person acting under your supervision may administer a product prescribed under the cascade; however, the prescription and use of the product remains your responsibility.


Only vets registered with the RCVS may prescribe medicines under the Cascade.

A Suitably Qualified Person (SQP) may retail supply an authorised veterinary medicine that falls within the scope of the registration they hold, against a prescription from a vet for use under the prescribing cascade.

A pharmacist may dispense authorised veterinary and human medicines, and extemporaneous preparations they have prepared against a prescription from a vet.

Food-producing species

The following conditions apply when prescribing a product under the Cascade for use in food-producing species:

  • the pharmacologically active substances contained in the medicine must have an Maximum Residue Limit (MRL), but not necessarily in the species for which it is intended to be used. For more information see the table of allowed substances in EU Commission Regulation 37/2010.

  • the vet responsible for prescribing the medicine must specify an appropriate withdrawal period

  • the vet responsible for prescribing the medicine must keep specified records

Setting withdrawal periods

A withdrawal period is the length of time that must lapse between administration and the point the animal can be slaughtered to enter the food chain.

You are required to specify an appropriate withdrawal period to the animal produce when prescribing or administering a medicine to food-producing animals under the Cascade. When setting the withdrawal period, you must take into account known information about the use of the product on the authorised species when prescribing for another species.

If a product is used as authorised, for example, use of an imported product from another member state, the authorised withdrawal period should be followed.

The longer of the following two withdrawal periods should be applied when a medicine is given to an animal that it is not indicated for, or at a higher dose rate than recommended to an animal that the product is indicated for:

  • the minimum statutory withdrawal period
  • the withdrawal period stated on the product’s SPC

The minimum statutory withdrawal periods are:

  • 7 days for eggs and milk
  • 28 days for meat from poultry and mammals
  • 500 degree days for fish meat


As there is no minimum withdrawal period set for honey, you must set a suitable withdrawal period that will ensure no risk to consumer health. Further guidance is available by contacting the National Bee Unit.


A horse declared as non-food producing in its passport can be treated as a non-food animal under the Cascade.

A horse that has not been signed out of the food chain in its passport must be treated as a food-producing animal under the Cascade.

There is a list of substances essential for the treatment of horses. This legislation allows the use of certain substances in horses (declared as food or non-food producing in the passport) under the Cascade and with a statutory withdrawal period of six months.

Further information about the use of medicines in horses is available on the Horse medicines and record keeping requirements page.

Human medicines

You are not allowed to prescribe a human medicine simply because it is cheaper than using an authorised veterinary medicine.

A human medicine may be used in accordance with the Cascade and assuming you can justify the course of treatment based on animal welfare.

Human homeopathic products may be used in food producing animals under the rules of the Cascade, but only if the active substances are listed in Table 1 Allowed Substances of Commission Regulation No 37/2010. In this case, the statutory withdrawal period must be applied.

Human medicines and veterinary medicines containing the same active substance are not always interchangeable, and some animal species react differently to medicines, e.g. ibuprofen is poisonous to dogs; therefore, you must use your clinical judgement when prescribing a human medicine for use in an animal.

Extemporaneous preparations: Specials

Any medicine tailored for a particular animal or herd, prepared by a vet, a pharmacist, or a person who holds an appropriate manufacturing authorisation, is an extemporaneous preparation.

A veterinary prescription is needed to use an extemporaneous preparation under the Cascade, but this may be written or oral.

To prepare an extemporaneous preparation, the vet should contact a holder of a Specials Manufacturing Authorisation (ManSA), who is well prepared and equipped to prepare medicines of suitable quality.

A list of veterinary only Specials Manufacturers is available.

A list of combined human and veterinary Specials Manufacturers is available.

Further information on the manufacture of specials can be found on the Apply for a Manufacturing authorisation for veterinary medicines page.

Exemptions for Small Pet Animals

Medicines marketed under the Exemption for Small Pet Animals are available over the counter and may be used in accordance with the product’s labelling. If you wish to use one of these products not in accordance with its recommended use, this would be classed as use under the Cascade and considered an extemporaneous preparation.

Stock of medicines

You may keep human medicines, imported medicines and extemporaneous preparations in your possession for use under the Cascade. The amount held should be justified by the clinical need under the Cascade rules; these medicines should not be used as a first choice treatment in every situation. You should keep up to date with new authorisations and change your prescribing habits and stocking policies accordingly.


The information that must be included on the label for products used under the Cascade is listed in the Veterinary Medicines Regulations (VMR). If all or part of the information cannot be included on the label, you may include it on a separate sheet.

It is the responsibility of the person supplying the medicine to ensure it is appropriately labelled.

Record keeping

As well as the normal record keeping requirements there are specific requirements for vets who administer or supply medicines under the Cascade.

These must be kept for 5 years and made available upon request from a duly authorised person. The records that must be retained are listed in the VMR.

Adverse events

You do not have to report adverse events to medicines prescribed under the Cascade, but we encourage you to do so. Guidance is available on reporting adverse events.

Practical considerations

Cascade use vs Authorised use

Authorised use is when a product is used in accordance with the clinical advice given on the product’s SPC. The SPCs for all authorised veterinary medicines are available on the Product Information Database.

Cascade use is when a veterinary medicine is used in another species or to treat another disease.

It is not always clear what the difference is, so some examples are given below.

Scenario Cascade use Authorised use
SPC dose regimen is 10 mg per kg for 3 days and the applied dose regimen is 20 mg per kg for 3 days Yes No
SPC dose regimen is 10mg per kg but this is extended in duration from a recommended 3 days to 6 days if from days 4 to 6 if from days 1 to 3
SPC dose is 10 mg per kg for 6 days and the applied dose regimen is 20 mg per kg for 3 days Yes No
SPC includes special warnings concerning the use of the product in animals with kidney disease but the animal to be treated has kidney disease No as long as special warnings are followed
Anticancer drug indicated for use in dogs with tumours with specific genetic markers – used in dogs with tumours not displaying the markers or the tumour markers are not established Yes No
SPC for the vaccine specifies primary vaccination in animals from 10 weeks of age or older, and animals are 12 weeks at the time of vaccination No Yes
SPC for the vaccine recommends a primary schedule of vaccination at 6 and 12 weeks but the animal to be treated is vaccinated at 8 and 14 weeks No Yes

Special considerations for the responsible use of antibiotics under the Cascade

The VMD supports and encourages the responsible use of antibiotics. Please read our Summary Position Statement on this topic.

Special considerations for use of vaccines under the Cascade

Where the SPC for a vaccine specifies a booster vaccination for a component after three years, but an annual booster vaccination is carried out this is Cascade use.

Where an animal is to be revaccinated beyond the period of the authorised schedule (e.g. an adult dog being revaccinated sometime after puppy vaccinations) there is no need for you to use the same product on the animal as was used previously. Vets should make a benefit:risk assessment taking into account current knowledge concerning the individual disease against which they are vaccinating. For example, there may be no real justification for administering a full primary puppy vaccination course for the World Small Animal Veterinary Association (WSAVA) recommended core antigens (i.e. Distemper, Adenovirus and Parvovirus) when a dog’s booster vaccination schedule has been allowed to lapse, as a single dose of vaccine may be sufficient to provide adequate immunity. This is not the case for antigens, such as, leptospira and so it is important for vets to make a benefit:risk assessment in relation to the specific animal and its circumstances.

Simultaneous and concurrent use of vaccines

Where SPCs specifically state that two named vaccines can be administered concurrently or simultaneously, this will be authorised use.

Where there is no such SPC statement, concurrent or simultaneous administration represents Cascade use. A decision to use a vaccine before or after any other veterinary medicine needs to be made on a case by case basis by the vet.

Use of a route of administration other than the authorised route

Use of an unauthorised route of administration could have serious consequences for the animal, the owner, the environment and the consumer if the attenuated virus behaves differently when administered by a different route (for example, administering a vaccine intended for intramuscular administration in drinking water or feed).

Examples of how the Cascade may be applied

Dosage considerations

Sometimes a vet may consider that the effective treatment of a particular condition in a particular animal requires a different dosage regime from that on the label of a product. In such circumstances recourse to the Cascade would be appropriate and the vet may compare the merits of using that product with a dosage regime different from that described on the product’s SPC with an alternative authorised veterinary medicine.

If neither can safely be administered at the dosage required, the vet should consider further options under the Cascade.

Individual characteristics

If a particular animal has characteristics, such as age, general condition or known sensitivity to a particular substance, which the vet judged to present unacceptable risks and to contra-indicate the use of the authorised product, they could conclude that no authorised product existed for that condition in that animal and consider other treatments.

Chronic infections

If a condition persists following treatment with an authorised product, the vet may consider in a particular case that there is no authorised treatment for that particular condition and that further use of medicines containing substances in the same chemical group is not appropriate. In such circumstances the vet can consider alternatives in accordance with the Cascade.

Complex conditions

Diagnosis is a matter for the prescribing vet. Some conditions need to be viewed more widely and treated accordingly. For instance, pneumonia may be regarded as a single condition. On the other hand, the diagnosis may be of more than one concurrent condition, such as pneumonia with fluid retention. In such circumstances the vet would need to exercise their professional skills to reach a diagnosis and prescribe the most effective treatment.

If the vet considered that in the circumstances there were two or more concurrent conditions, the treatment of each would need to be considered. However, factors such as drug incompatibilities or side-effects must be considered.

Unavailability of product

If a product cannot be obtained despite diligent search and in a reasonable time, the vet may conclude that in these circumstances it does not exist. In such circumstances the Cascade should be followed to identify a suitable alternative. However, it is appreciated that there may be cases where urgency dictates that a vet uses whatever is to hand, whether authorised or not. The VMD publishes details of supply issues which have the potential to cause animal welfare issues and provides where possible information on alternative products.

Animal owner considerations

The vet should take into account the owner of the animal when prescribing. For example, if a vet considers that an elderly or disabled pet owner would have difficulty in crushing and administering tablets which were the only form in which an authorised product was available, they could consider alternatives in line with the Cascade.

Medicines commonly found around the home

Sometimes a vet may judge there is a need to alleviate a pet’s discomfort until a home visit can be made or the animal brought to the surgery. It would be unlikely that action would be taken if in an emergency a vet recommended that an animal owner could use a human medicine that the owner already has in their possession (for example, antihistamine tablets). This does not mean a pet owner should be encouraged to go into a pharmacy and ask for a human medicine for their pet.


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Published 1 June 2015
Last updated 30 October 2015 + show all updates
  1. Correction to the steps, in descending order of suitability,
  2. First published.