Types of Antidepressants
The history of antidepressants begins with the tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs). Both of these classes of antidepressants were successful and were discovered by chance. The first antidepressants became available in the late 1950s.
Newer antidepressants such as the SSRIs have largely replaced older TCAs and MAOIs as first-line depression drugs. However, Tricyclic antidepressants and MAOIs remain valuable alternatives for patients with moderate to severe depression.
All antidepressants work on the principle of enhancing one or more of the neurotransmitters in the brain. Neurotransmitters are molecules that specialize in delivering packets of information from one neuron to another.
Important to know: Neurotransmitters cannot be taken orally or intravenously because they cannot pass the brain-blood barrier.
Classification of Antidepressants
There are many different types of antidepressant. Antidepressants are put into groups based on which chemicals in the brain they affect. Main classes of antidepressant include:
Selective Reuptake Inhibitors
Selective Serotonin Reuptake Inhibitors
Selective Serotonin Reuptake Inhibitors (SSRIs) act only on the neurotransmitter serotonin, while tricyclic antidepressants and MAO inhibitors act on both serotonin and another neurotransmitter, norepinephrine, and may also interact with other chemicals throughout the body. Selective serotonin reuptake inhibitors have fewer side effects than tricyclic antidepressants and MAO inhibitors. Some of the side effects that can be caused by SSRIs include dry mouth, nausea, nervousness, insomnia, headache and sexual problems.
The tricyclics have been used to treat depression for a long time. Imipramine was discovered in the early 1950s, and was the first tricyclic antidepressant.
TCAs act on both serotonin and another neurotransmitter, norepinephrine, and may also interact with other chemicals throughout the body. Common side effects caused by these medicines include dry mouth, blurred vision, constipation, difficulty urinating, worsening of glaucoma, impaired thinking and tiredness.
Amoxapine (Asendin) is very rarely used because of severe extrapyramidal side effects.
Serotonin and Norepinephrine Reuptake Inhibitors
Serotonin and norepinephrine reuptake inhibitors (SNRIs) works by slowing down the reuptake of both serotonin and noradrenaline, but more selectively than other antidepressant drugs.
Norepinephrine and Dopamine Reuptake Inhibitors
NDRIs block the reuptake of neurotransmitters norepinephrine and dopamine, increasing the levels of these neurotransmitters in the synapses.
Combined reuptake inhibitors and receptor blockers
Trazodone and nefazodone are phenylpiperazine antidepressants.
Trazodone is a serotonin reuptake inhibitor and is also a 5-HT2 receptor antagonist. This results in more serotonin to stimulate other nerves. This medication has sedative and antidepressant properties.
Nefazodone works by inhibiting the uptake by nerves of serotonin and norepinephrine. Nefazodone is chemically related to trazodone, and shares its actions. Nefazodone has a lesser risk of priapism.
Noradrenergic and Specific Serotonergic Antidepressants
The novel antidepressant mirtazapine has dual mode of action. It is a noradrenergic and specific serotonergic antidepressant that enhances noradrenergic and serotonergic neurotransmission. Mirtazapine has been proved effective in the treatment of patients who were resistant or intolerant to SSRIs.
Monoamine oxidase inhibitors (MAOIs)
MonoAmine Oxidase Inhibitorsare are the oldest class of antidepressants developed in the 1950s. MAOI work by increasing the availability of the monoamine transmitters; norepinephrine (NE), dopamine (DA), and 5- hydroxytryptamine (5-HT), by blocking their metabolism.
Relative Toxicity with Overdose
Therapeutic and Adverse Effects of Antidepressants
References & Resources
Published: May 05, 2007