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The new antidepressants
Editor, – I refer to the articles by Professor J. Tiller (Aust Prescr1995;18:92-6) and Professor G. Shenfield (Aust Prescr 1995;18:100-1) on the new antidepressants. The new drugs are being compared with tricyclics (TCAs) in a way which one can only describe as disingenuously simplistic. The tricyclics are a heterogeneous group and vary greatly in their binding affinity at various receptors. For instance, desipramine is 1000-fold more potent, as a noradrenaline reuptake inhibitor, than trimipramine. Also plasma levels of TCAs vary greatly. Thus, comparing all 'TCAs' with SSRIs is misleading. Comparing therapeutic levels of desipramine and nortriptyline would be more appropriate.
The statement by Professor Shenfield regarding MAOIs that 'numerous serious interactions with a range of other drugs including TCAs.....' requires putting into perspective. Despite treating about 1000 patients with MAOIs in my career, I have rarely seen even minor morbidity from hypertensive reactions, which are easily treatable. I have managed many thousand 'patient years' of combinations(of MAOIs with TCAs) and never seen problems (one avoids clomipramine and imipramine which have clinically significant serotonin reuptake inhibition capacity).
In contrast, I have seen quite a few serious serotonin syndrome reactions already and a computer search shows a rapid increase in reports from 8 in1992, to 16 in 1994, and 12 in the first 7 months of 1995. There is no effective treatment for this potentially fatal interaction; bathroom cupboards every where now contain both moclobemide and SSRIs; individually very safe, when combined, potentially fatal.
Mount Pleasant, Qld