The prescribing cascade

Veterinary medicinal products (VMPs) must be administered in accordance with the prescribing cascade, as set out in The Veterinary Medicines Regulations 2013. These Regulations provide that when no authorized VMP exists for a condition in a particular species, veterinary surgeons exercising their clinical judgement may, in particular to avoid unacceptable suffering, prescribe for one or a small number of animals under their care other suitable medications in accordance with the following sequence:

  1. A VMP authorized in the UK for use in another species with the same condition, or for a different condition in the same species.
  2. A medicine authorized in the UK for human use or a VMP authorized in another EU member state for use in any species under the Special Import Scheme.
  3. A VMP prepared extemporaneously by a properly authorized person as prescribed by the veterinary surgeon.

‘Off-label’ use is the use of medicines outside the terms of their marketing authorization. It may include medicines authorized outside the UK that are used in accordance with an import certificate issued by the VMD. A veterinary surgeon, with detailed knowledge of the medical history and clinical status of a patient, may reasonably prescribe a medicine ‘off-label’ in accordance with the prescribing cascade. Authorized medicines have been scientifically assessed against statutory criteria of safety, quality and efficacy when used in accordance with the authorized recommendations on the product literature. Use of an unauthorized medicine provides none of these safeguards and may, therefore, pose potential risks that the authorization process seeks to minimize. Note that the use of an ESPA medicine not in accordance with the product’s labelling would be classed as use under the cascade and considered an extemporaneous preparation.

Medicines may be used ‘off-label’ for a variety of reasons including:

  • No authorized product is suitable for the condition or specific subpopulation being treated
  • Need to alter the duration of therapy, dosage, route of administration, etc., to treat the specific condition presented
  • An authorized product has proved ineffective in the circumstances of a particular case (all cases of suspected lack of efficacy of authorized veterinary medicines should be reported to the VMD).

He or she should inform the owner of the reason why a medicine is to be used ‘off-label’ and record this reason in the patient’s clinical notes. When electing to use a medicine ‘off-label’ always:

  • Discuss all therapeutic options with the owner
  • Use the cascade to determine your choice of medicine
  • Obtain signed informed consent if an unauthorized product is to be used, ensuring that all potential problems are explained to the client
  • Administer unauthorized medicines against a patient-specific prescription. Do not administer to a group of animals if at all possible.

An ‘off-label’ medicine must show a comparative clinical advantage to the authorized product in the specific circumstances presented (where applicable). Medicines may be used ‘off-label’ in the following ways (this is not an exhaustive list):

  • Authorized product at an unauthorized dose
  • Authorized product for an unauthorized indication
  • Authorized product used outwith the authorized age range
  • Authorized product administered by an unauthorized route
  • Authorized product used to treat an animal in an unauthorized physiological state, e.g. pregnancy (i.e. an unauthorized indication)
  • Product authorized for use in humans or a different animal species to that being treated.

Adverse effects may or may not be specific for a species, and idiosyncratic reactions are always a possibility. If no adverse effects are listed, consider data from different species. When using novel or unfamiliar drugs, consider pharmaceutical and pharmacological interactions. In some species, and with some diseases, the ability to metabolize/excrete a drug may be impaired/enhanced. Use the lowest dose that might be effective and the safest route of administration. Ensure that you are aware of the clinical signs that may suggest toxicity.

Information on ‘off-label’ use may be available from a wide variety of sources ().

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