Compare and contrast the mechanism of action and side effects of tricyclic antidepressants, selective serotonin reuptake inhibitors and monoamine oxidase inhibitors.

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College Answer

Good answers were in tabular format.
The antidepressant action is similar for each agent. Initial increase in 5HT and NA, followed
in 2-3 weeks by a down regulation or change in efficiency of 5HT transmission. The agents
produce elevated neurotransmitters via different mechanisms, either reuptake blockade or
enzyme inhibition. MAOIs can be competitive or non-competitive. Mention of the different
neurotransmitters affected by each agent was required.
A description of significant side effects at therapeutic doses, and in overdose was expected
with explanations provided. These should have included - the anticholinergic effects and
cardiotoxicity of TCAs, postural hypotension, the catecholamine, pethidine and tyramine
related complications of MAOIs, and serotonin syndrome with SSRI/MAOI use and or
overdose. More marks were gained for mention that side effect profiles can be beneficial e.g.
analgesic properties of TCAs, sedation with TCAs/ SSRIs and energizing benefits of
SSRIs/SNRIs. SSRI’s safety and efficacy have markedly reduced the use of MAOIs and to a
lesser extent TCA’s..
Syllabus G2f2d
Reference: Stoelting p 398-407
Katzung p 476-487.