Abstract
P. K. Gillman Mount Pleasant, Qld, Australia:
As a warning for general practitioners (GPs), Beerworth and Tiller's article [1] is important but specialists need a more detailed knowledge of toxicology. It is not accurate to take the approach of lumping the tricyclic antidepressants (TCAs) nor the selective serotonin re-uptake inhibitors (SSRIs) and other new drugs together in considering either their side effects or toxicity.
The mechanisms of the toxic (proconvulsant and cardiotoxic) effects of drugs are still poorly understood but are not ‘class’ related [2]. The intraclass variations in toxicity are large, and of a similar order of magnitude to the interclass variations. An example is clomipramine (and lofepramine, not presently available in Australia), which may be about 10 times less toxic than desipramine or dothiepin [3] and of similar, or lesser, toxicity to some of the new drugs. However, the ‘toxicoepidemiology’ evidence (see Buckley [4]) from which one might make confident judgements is not yet available, although there are indications that one or two of the newer drugs may be as toxic as some TCAs.
Ironically, as mentioned by Beerworth and Tiller, it may turn out that the toxicity of SSRIs and moclobemide is significantly elevated when they are coingested. This may be more frequent and dangerous than is currently appreciated [5], [6], but again, we simply do not have sufficient quality data to make firm judgements.
There are also very large differences in toxicity between individual drugs within all other classes or groups of psychotropics (e.g. anticholinergics, see Buckley [7]). Beerworth and Tiller's article reinforces the importance of detailed awareness of these factors for optimal prescribing.