Anti-Depressants | MOIs

Question 1

What are some of the drugs found in this class?

Answer 1

A. Selective Medications (MO-B) (mainly used for Parkinson’s disease)
1. Selegiline
2. Rasigiline
B. Non-selective Medications: (MO-A&B)
1. Isocarboxazid
2. Phenelzine
3. Tranylcypromine

Question 2

What is their mechanism of action?

Answer 2

They work by inhibiting monoamine oxidase enzymes which increases the levels of neurotransmitters that are decreased by depression and they are of two types:
1. Selective: blocking only MO-B which increases dopamine levels only

2. Non-selective: blocking MO-A&B which increases the levels of both dopamine, norepinephrine and serotonin.

Question 3

What are their indications?

Answer 3

1. Selective: Parkinson’s disease (can also be used for depression, not very effective)
2. Non-selective: atypical depression (mainly) and major depressive disorder. However it should be noted that it’s the second or third line medication due to the fact that it can increase the levels of all 3 neurotransmitters.

Question 4

What are their side effects?

Answer 4

1. Serotonin Syndrome (antidote: cyproheptadine)
2. Hypertensive Crisis:
   Tyramine-rich foods (meat, beer) –> MO-A&B in gut cells –> breakdown, when MOIs are given, tyramine builds up and increases norepinephrine levels leading to hypertensive crisis. Antidote: phentolamine