MAO inhibitors in psychiatry

Editor, – I would like to respond to Associate Professor Evans' concluding remarks (Aust Prescr 1993;16:59-60) regarding the new reversible MAO-A inhibitor moclobemide. He suggests tricyclics (TCAs) should be 'the treatment of first choice for most patients with major depressive disorder' and that TCAs 'are effective and safe when (my emphasis) used properly and we know (my emphasis) how to use them properly'. Hence, he suggests moclobemide occupies a second order or lesser status.

In 1990, 386 Australians (source: ABS) died by suicide by ingestion of solid and liquid substances. A Brisbane survey of overdose fatalities¹ suggests that TCAs account for about 10% of these suicides (i.e. 10% of 386). Hence, TCAs kill about 38 Australians a year by over dosage alone. Professor Evans gives brief mention of the overdose issue which does not do justice to this mortality nor the reality that depression is associated with more than 50%of all suicides (all methods). Saying that TCAs are 'safe when used properly' reminds me of the outmoded attitudes of the motor vehicle industry - that cars are safe when driven properly! Also, we do not know how to use TCAs properly for the simple reason that the ability of psychiatrists (not to mention others) to predict which patients will overdose is dismal.

I suggest that in considering which antidepressants to use, the potential for overdose is a vital consideration. As we cannot reliably predict suicide, I advocate that the newer less toxic antidepressants should be first-line drugs in patients at significant risk. I say this acknowledging the hazard of the unknown associated with new drugs (e.g. zimelidine and nomifensine - 'new' antidepressants which were subsequently withdrawn). In my opinion, tricyclics generally maybe first-line drugs in those patients who one is confident will not overdose.

Dr Chris Cantor
Suicide Research and Prevention Program
Princess Alexandra Hospital
Woolloongabba, Qld

Associate Professor L. Evans, the author of the article, comments:
As I understand it, Dr Cantor is critical of my opinion that the tricyclics are still the first treatment of choice for major depressive disorder. The argument is that approximately35 people per year kill themselves with tricyclics in Australia. I'm pleased he has made this argument as it is being put to doctors to suggest that they prescribe the newer and certainly much more expensive antidepressants instead of the older cheaper tricyclics. However, there is good evidence to show that removing a drug or particularly noxious agent which is popular as a means of suicide does not cut down the suicide rate. What it does do is transfer those who wish to kill themselves to some other means of doing so. In Britain the suicide rate dropped with the introduction of the tricyclic antidepressants, but did not decrease at the time the barbiturates were withdrawn and the benzodiazepines introduced. To use the motor vehicle analogy, restricting tricyclics would be as logical as preventing depressed people having access to car keys, as we know the car to be the means of suicide for many, or to prevent them from going into supermarkets or chemist shops which abound with drugs which can be fatal.

I am not sure that Dr Cantor is right about the newer antidepressants being less toxicin overdose, although I hope he is. I commented that drugs should be viewed with suspicion as to their lethality in overdose until their toxicity is known. For example, it took quite a long time for the evidence of the lethality of paracetamol in overdose to emerge. In my view, the real concern about the lethality of drugs and their prescription relates to people who have easy access to medications commonly used for minor sedative or analgesic purposes who may then take them impulsively at times of crisis without actually intending suicide or even self-harm. Relating this to the tricyclics reinforces the view that they should not be prescribed indiscriminately, particularly as night sedation, not that they shouldn't be used as inferred by Dr Cantor.