Monoamine Oxidase Inhibitors (MAOIs) – Antidepressants

by Pravin Shukle, MD

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    00:01 Let's start off with the monoamine oxidase inhibitors. Monoamine oxidase reduce the breakdown of norepinephrine and serotonin in the pre-synaptic neuron. So you can see there that the MAO inhibitors are acting at the level of the pre-synaptic neuron to reduce the breakdown of those drugs before they are even released. The increased amounts of norepinephrine and serotonin are then stored in the vesicles. So vesicles is Latin for bag. So they have little bags of hormone at the end of these nerve terminals and they become ready for use. When the nerve fibers are firing, the increased amount of transmitter is then released into the synaptic cleft and so you have more post-synaptic stimulation. That's how MAO's work. Monoamine oxidase inhibitors can be selective and non- selective. The non-selective monoamine oxidase inhibitors include a large list of drugs including phenelzine and tranylcypromine. These are the two that I want you to remember.

    01:13 You don't have to remember obviously the 21 others for your exam. The more selective MAO-A inhibitors include Mannerix or moclobemide. Now this is a prototypical drug. This is the one that you will probably be tested on. The selective MAO-B inhibitor is selegiline and it's also used in Parkinson's disease. This is a prototypical drug. There are many many MAO-B inhibitors that are selective and you don't need to know them all. Side effects to MAO-A's and MAO-B's are usually due to increased norepinephrine in the nerve terminals. So this means peripheral autonomic sympathomimetic effects that we covered before in our autonomic nervous system lectures. It may actually lower blood pressure and it may reduce the seizure threshold. Which means that you have an increased risk of seizures with MAO's. Why is it that MAO's can cause a reduction in blood pressure. Well you have to remember that MAO's are being given in the absence of indirect sympathomimetics.

    02:23 And that's how they cause a drop in blood pressure. So it's not just about sympathomimetic activity, it's about which type of sympathomimetic activity you are endangering. Now in the presence of an indirect sympathomimetic, MAO's cause a large rise in blood pressure. MAO's in fact may cause severe hypertension in patients taking tyramine. So tyramine is a precursor to adrenaline and it is metabolized by monoamine oxidase. Now, tyramine is found in aged cheeses, in soybean, in beers and in red wine. And it's also found in cured and processed meats. So a meal like this to a patient who is taking a monoamine oxidase inhibitor can be quite deadly because it can cause severe hypertension. This is the great drawback of MAO's.

    About the Lecture

    The lecture Monoamine Oxidase Inhibitors (MAOIs) – Antidepressants by Pravin Shukle, MD is from the course CNS - Pharmacology.

    Included Quiz Questions

    1. Selegiline: non-specific MAOI: depression
    2. Selegiline: MAO-B inhibitor: Parkinson's disease
    3. Phenelzine: non-specific MAOI: depression
    4. Tranylcypromine: non-specific MAOI: depression
    5. Moclobemide: MAO-A inhibitor: depression

    Author of lecture Monoamine Oxidase Inhibitors (MAOIs) – Antidepressants

     Pravin Shukle, MD

    Pravin Shukle, MD

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    like it very much
    By Louis S. on 28. November 2017 for Monoamine Oxidase Inhibitors (MAOIs) – Antidepressants

    Hi ! You explain very well it's very understandable! Thank you very much !