|
Pharmacology => Drug => Antidepressant
Antidepressant
INTRODUCTION
Antidepressant, medication used to treat depression, a mood disorder characterized by such symptoms as sadness, decreased appetite, difficulty sleeping, fatigue, and a lack of enjoyment of activities previously found pleasurable. While everyone experiences episodes of sadness at some point in their lives, depression is distinguished from this sadness when symptoms are present most days for a period of at least two weeks. Antidepressants are often the first choice of treatment for depression.
HOW ANTIDEPRESSANTS WORK
Although the cause of depression is unknown, researchers have found that some depressed people have altered levels of chemicals called neurotransmitters, chemicals made and released by nerve cells, or neurons. One neuron, referred to as the presynaptic neuron, releases a neurotransmitter into the synapse, or space, between the neuron and a neighboring cell. The neurotransmitter then attaches, or binds, to a neighboring cell-the postsynaptic cell-to trigger a specific activity. Antidepressants work by interacting with neurotransmitters at three different points: they can change the rate at which the neurotransmitters are either created or broken down by the body; they can block the process in which a spent neurotransmitter is recycled by a presynaptic neuron and used again, called reuptake; or they can interfere with the binding of a neurotransmitter to neighboring cells.
TYPES OF ANTIDEPRESSANTS
The first antidepressants, developed in the 1950s, are the tricyclic antidepressants (TCA) and the monoamine oxidase (MAO) inhibitors. TCAs block the reuptake of neurotransmitters into the presynaptic neurons, keeping the neurotransmitter in the synapse longer, and making more of the neurotransmitter available to the postsynaptic cell. TCAs include amitriptyline, doxepin, imipramine, nortriptyline, and desipramine.
MAO inhibitors decrease the rate at which neurotransmitters are broken down by the body so they are more available to interact with neurons. MAO inhibitors currently available in the United States include phenelzine and tranylcypromine.
Another group of antidepressants, known as selective serotonin reuptake inhibitors (SSRI), became available in 1987. SSRIs block the reuptake of the neurotransmitter serotonin into presynaptic neurons, thereby prolonging its activity. There are currently four SSRIs available for use in the United States: fluoxetine, sertraline, paroxetine, and fluvoxamine. Of this group, the best known is fluoxetine, commonly known by its brand name, Prozac.
Another antidepressant is venlafaxine, which works like TCAs but does not share their chemical structure, and it also causes different side effects. The antidepressant nefazodone prevents serotonin from binding to neighboring neurons at one specific binding site (serotonin can bind to neurons on many sites). It also weakly blocks the reuptake of serotonin.
EFFECTIVENESS AND SIDE EFFECTS
All antidepressants decrease symptoms of depression in about 70 percent of depressed people who take them. Most antidepressants take about two to three weeks of treatment before beneficial effects occur. Because no antidepressant is more effective than the others, doctors determine which antidepressant to prescribe according to the type of side effects an individual can tolerate. For instance, a person who takes TCAs and MAO inhibitors may notice dizziness and fainting when standing up, mouth dryness, difficulty urinating, constipation, and drowsiness. If people who take MAO inhibitors eat certain foods, such as aged cheese or some aged meats, they can experience severe headaches and raised blood pressure. SSRIs can cause side effects such as restlessness, difficulty sleeping, and interference with sexual function.
Back
|
