Guidance

The cascade: prescribing unauthorised medicines

Guidance for prescribing vets on the use of the cascade.

Veterinary medicines are authorised for specific conditions for specific target species, based on assessed data. The conditions of use for each authorised veterinary medicine are listed in its Summary of Product Characteristics (SPC). The VMD’s Product Information Database contains the SPCs of all veterinary medicines authorised in the UK.

Where there is no suitable veterinary medicine authorised in the UK for the specific condition in the animal being treated, in particular to avoid unacceptable suffering, vets are permitted to use their clinical judgement to treat animals under their care in accordance with the cascade.

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.

Prescribing decisions under the cascade should be made on a case by case basis. For example, if a suspected adverse event occurred when using a medicine in an animal, this does not mean that the cascade should always be used when treating other animals.

The prescribing vet is personally responsible for the choice of product and, as part of the Royal College of Veterinary Surgeons (RCVS) Code of Professional Conduct for Veterinary Surgeons, must obtain the owner’s consent for their animal to be treated under the cascade. They must also maintain accurate records.

The prescribing vet, or a person acting under their supervision, may administer a product prescribed under the cascade; however the prescription and use of the product remains the vet’s responsibility.

When using a product under the cascade, the vet should balance the expected benefits to the animal with the risks of using a medicine under the cascade. 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

When prescribing medicines under the cascade, vets must ensure that the evidence base for their prescribing decisions is robust and complies with Recognised Veterinary Practice (RVP). This is particularly important when prescribing medicines lower down the cascade; if the treatment does not comply with RVP it may require licensing by the Home Office as a regulated procedure under the Animal (Scientific Procedures) Act. Further guidance on RVP is available from the RCVS.

Dispensing

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 (Table 1) 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 the final administration of the medicine and the point the animal can be slaughtered to enter the food chain or when produce is taken.

The prescribing vet is required to specify an appropriate withdrawal period when prescribing or administering a medicine to food-producing animals under the cascade. When setting the withdrawal period, the vet 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.

Where the product is not used as authorised, for example, when a higher dose is used, or a species for which the product is not indicated is treated, then care needs to be taken to ensure that a suitable withdrawal period is set. This ensures that no residues of veterinary medicines above the MRL remain at the time of slaughter or when produce is taken.

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

However, in cases where the authorised withdrawal periods are close to, or longer than, the ‘statutory minimum’ withdrawal periods, the vet should consider other factors when setting a suitable withdrawal period. Factors to consider include:

  • The length of the authorised withdrawal period(s)
  • The known pharmacokinetics of the active substance(s) in both the authorised species and the species being treated (if different)

The vet could, for example, increase the authorised withdrawal period by 50% (where a 30 day withdrawal period is authorised in cattle (meat and offal), a 45 day withdrawal period might be suitable for goats).

If a higher dose is given, then a longer period may be warranted.

Honey

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

Horses

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 guidance page.

Human medicines

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

Human medicines and veterinary medicines containing the same active substance may not be interchangeable.

Importing Medicines under the cascade

In order to legally import medicines for use under the cascade, an Import certificate must be obtained from the VMD under the Special Import Scheme. Failure to obtain a certificate for an imported veterinary product is an offence under the Regulations.

Further information on how to apply for an import certificate is published along with the link to the online application system.

Cascade use when new products come to market

If an authorised veterinary medicine becomes available while an animal is already being treated for a condition under the cascade, the prescribing vet should consider transferring the animal onto the authorised veterinary medicine. However, if the vet has concerns that changing the product could compromise the stability of the patient’s condition, it may be acceptable to continue treatment under the cascade. Any new cases should receive the authorised veterinary medicine.

Extemporaneous preparations

Extemporaneous preparations and the cascade

Extemporaneous preparations (also known as “veterinary specials”) are products that do not hold a marketing authorisation (MA). These products have not been assessed by the VMD against the same standards of quality, safety (for the target animal, user, consumer and environment) and efficacy as authorised veterinary medicines. They can legally be prescribed, supplied and used under the last tier of the cascade.

Vets should recognise that, as the last tier of the cascade, extemporaneous preparations carry a higher risk than authorised medicines and should take this into account when prescribing them. There are further requirements for labelling and record keeping under the cascade.

Manufacturers of extemporaneous products must be authorised, that is hold a ManSA, and comply with the general principles of good manufacturing practice (GMP). Their facilities, equipment and procedures are regularly inspected by the VMD to ensure they manufacture extemporaneous products to a set quality standard.

During inspections of veterinary practice premises (VPPs) both the VMD and RCVS will inspect supplies of products used under the cascade and associated records.

Registers

Further information on the manufacture of extemporaneous preparations can be found on the Apply for a manufacturing authorisation for veterinary medicines guidance 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 vets 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

Vets may keep limited quantities of human medicines, imported medicines and extemporaneous preparations in their possession for the treatment of animals where cascade use is required. The amount held should be justified by the immediate clinical need under the cascade rules. These medicines should not be used as a first choice treatment in every situation. Vets should keep up to date with new authorisations and change their prescribing habits and stocking policies accordingly.

Labelling

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, vets 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.

The RCVS requires that consent must be obtained from clients before prescribing 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

The VMD encourages vets to report adverse events to all medicines. This includes those prescribed under the cascade, including veterinary medicines used outside the terms of their marketing authorisation, human medicines and extemporaneous preparations. 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.

A product’s SPC is based on assessed data and details the advice for correct administration, precautions and warnings to ensure safe and effective use of the product. The cascade permits deviations from the SPC when a suitable authorised product is not available. Any such deviations should be based on robust clinical reasons, with the individual prescribing vet taking responsibility for use under the cascade.

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 product behaves differently when administered by a different route (for example, administering a vaccine intended for intramuscular administration in drinking water or feed).

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, for example, an adult dog being revaccinated sometime after puppy vaccinations, there is no need for the vet 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, such as 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 other 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.

Examples of how the cascade may be applied

Individual characteristics

If a particular animal has characteristics, such as age, general condition or known sensitivity to a particular substance, which the vet judges 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.

Unavailability of product

If a product cannot be obtained despite a thorough 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.

If vets cannot obtain authorised products from their usual wholesaler, they may issue a written prescription for the animal owner to use with another supplier.

Animal owner considerations

The vet should take into account the animal owner’s ability to administer the medicine when prescribing. For example, a vet may conclude that an animal owner would have difficulties in administering the authorised product (for example due to age or disability). In the interest of animal welfare and treatment compliance the vet could consider an alternative treatment under 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, such as, 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.

Responsible use of antibiotics

The VMD has published guidance on the responsible use of antibiotics under the cascade.

To minimise the development of antibiotic resistance, where a particular antibiotic is shown to be effective against a bacterial pathogen (for example by culture and sensitivity data), it is acceptable to prescribe a narrow spectrum antibiotic under the cascade instead of a broad spectrum antibiotic that has an authorised indication for the condition being treated.

Contact

By email, quote Use of the Cascade in the subject line to postmaster@vmd.gov.uk

Published 1 June 2015
Last updated 20 June 2019 + show all updates
  1. Reviewed and updated to add further clarification
  2. Correction to the steps, in descending order of suitability,
  3. First published.