Challenging drug classifications

Shakespeare said that a rose by any other name would smell as sweet.

A dose by any other name would be just as good to treat. And probably better – since a new system of nomenclature based on neurobiology will free our thinking.  

The WHO-approved system first published in 1976 introduced the ATC (Anatomical, Therapeutic, Chemical) classification. But, at least in psychiatry, it has been outgrown by advances in psychopharmacology and by our expanding armamentarium of agents: currently well over one hundred drugs are used in psychiatry, and the same type of drug is often used for many different purposes.

Some “antipsychotics”, for example, are also approved as antimanics and even antidepressants.  And it may seem a subtle difference, but talking of “drugs for depression” rather than “antidepressants” is preferable since it does not imply that treating depression is their only use.

Instead, we will have a “multiaxial” classification including a drug’s primary pharmacological target and mode of action, the relevant neurobiology, clinical observations of efficacy and side effects, and indications.  Classifying by indication will no longer be the main focus.

The current ATC system has been terminally challenged by the development of drugs with multiple and complex modes of action. It included classes such as non-selective monoamine reuptake inhibitors and SSRIs but had a catch-all category of “other” which has become swamped by the flood of new agents.

The category of tricyclic antidepressants is based on chemical structure but conveys little clinically useful information and tells us nothing about mode of action. 

SSRI is a reasonable concept, but the term SNRI has led to great confusion about how these drugs work. Yet, in response to a survey by the task force developing the new nomenclature, more than 80% of psychiatrists said that the SSRI/SNRI distinction affected their prescribing decisions!

We currently have a restricted number of words to describe drugs. And this is restricting our ability to think constructively about what we are doing. We should be like the Eskimos who have developed many words for snow to reflect important distinctions in their experience. So “serotonin dopamine antagonist” is far preferable to “second generation antipsychotic” or even “atypical antipsychotic”. 

The new system is the fruit of four year’s work by an independent task force of experts representing learned societies from all quarters of the globe.  It is available as a pocket-sized book but, more importantly, as the freely-downloadable NbN app on Apple and Android phones.

What we have now is not the last word on this issue, but rather a work in progress, Professor Goodwin emphasised. It requires our help to make it better.