The Creation of Intensional Medication Lists Using the NHS Dictionary of Medicines and Devices.

The identification of medications prescribed to patients in routinely collected health records is an important part of the identification of cohorts for surveillance and research. Preparations available for prescription can change frequently and this presents challenges to the maintenance of extensional or "flat lists" of medications, particularly in ongoing studies such as disease surveillance. The NHS publishes a Dictionary of Medicines and Devices weekly, listing almost all the medications available in the UK as an extension to the UK edition of SNOMED CT. We developed a method of creating intensional specifications of medications using specified active ingredients and the form of the medication. The specifications can be expressed using the SNOMED CT Expression Constraint Language, and can be used to form a library which may be used across multiple projects. We have developed intensional definitions of medication groups for all drugs likely to be used in primary care. We have shown that these can be shared as FHIR valuesets using the NHS Terminology Server. Here we show examples of expressions about medications used for neuropathic pain. We have created expressions which improve the specificity of the extraction by filtering on the form and number of ingredients.