SSRIs, SNRIs and triptans

The cost to the system

Antidepressants make up the largest expenditure for medications of any category.

In 2000, the domestic sales of antidepressants in the U.S. totaled $10.4 billion, outweighing all other expenditures for medications. Of these sales, three antidepressants stood out in retail sales–fluoxetine (Prozac) at $2.6 billion, sertraline (Zoloft) at $1.9 billion, and paroxetine (Paxil) at $1.8 billion. Although some antidepressants are prescribed more often than others, there is no compelling reason to prescribe any one over another.

In 2004, antidepressants totaled $13 billion worldwide, with only 10 drugs on the market. Nine of these 10 face a loss of patent from 2006 to 2010. Predictions suggest this loss of patent means a nearly 50 percent loss of total revenues, bringing it down to about $7 billion.

Related material: Prescribing antidepressants

Types of antidepressants

About 62 percent of antidepressant prescriptions in the U.S. are selective serotonin reuptake inhibitors (SSRIs), which are the newest class of antidepressants. The other major classes are monoamine oxidase inhibitors (MAOIs) and tricyclics.

These major classes of antidepressants all operate on a similar assumption that mood is regulated in the brain by certain chemicals called neurotransmitters. Research suggests that abnormal activity in the monoamine neurotransmitters (norepinephrine, serotonin, dopamine) can affect mood and behavior. Antidepressants work by blocking nerve cells from reabsorbing these neurotransmitters, thus keeping more of these chemicals in the brain. This enhances neurotransmitter activity, which is thought to improve mood.

Treating depression with drugs

According to the National Institute of Mental Health (NIMH), SSRIs are the first line of treatment for anxiety and depressive disorders. When treating depression, antidepressants typically need to be taken for 6 to 8 weeks before the full therapeutic effect can be felt. Additionally, there is no way to know beforehand which medication will work, so often doctors will start with one for 6 to 8 weeks, then try another. On top of that, it’s recommended to continue medication for 6 to 12 months for full effectiveness and to prevent relapse of depression. In patients with a history of multiple bouts of depression, long-term use is recommended. If the first treatment doesn’t work, different antidepressants can be tried, or the original medication can be augmented with additional medications, such as aripiprazole (Abilify) or mirtazapine (Remeron).

Selective Serotonin Reuptake Inhibitors (SSRIs)

SSRIs work by blocking reabsorption of neurotransmitters in the brain, but this class of drugs specifically target the neurotransmitter serotonin. SSRIs are considered safer than MAOIs and tricyclics. They are less likely to have adverse interactions with other drugs, and they are less dangerous if overdosed.

Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)

SNRIs block reabsorption of both serotonin and norepinephrine, like the tricyclics. However, more like the SSRIs, these drugs selectively target only these two neurotransmitters. Because these drugs are similar to SSRIs, they share similar side effects. Since SNRIs also block norepinephrine, this creates additional side effects.

Monoamine Oxidase Inhibitors (MAOIs)

MAOIs work by preventing certain neurotransmitters from metabolizing, thereby increasing the amount of these chemicals in the brain. Most MAOIs act irreversibly, meaning that once an MAOI has altered the neurotransmitters, they stay altered until the body naturally replaces the affected neurotransmitters, which can take about two weeks.

MAOIs also react with certain foods and alcoholic beverages, such as aged cheeses, foods containing monosodium glutamate (MSG), Chianti and other red wines, and other medications, such as over-the-counter cold and allergy preparations, local anesthetics, amphetamines, insulin, some narcotics, and antiparkinsonian medications. Because of this, patients on MAOIs must adhere to strict diets and be closely monitored for adverse drug interactions.

Tricyclics

Tricyclics work by blocking the reabsorption of neurotransmitters at cell receptor sites. These drugs primarily target serotonin and norepinephrein, but they also affect other neurotransmitters, including dopamine, to a lesser degree. Not much is known about how these drugs work specifically, but they do interfere with other cell receptors, causing many of their side effects.

Tricyclics can interact with thyroid hormone, antihypertensive medications, oral contraceptives, some blood coagulants, some sleeping medications, antipsychotic medications, diuretics, antihistamines, aspirin, bicarbonate of soda, vitamin C, alcohol, and tobacco.

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Effectiveness of SSRIs
Risks and side effects
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