Tricyclic Antidepressants (TCAs)

Tricyclic antidepressants(TCAs) are a class ofantidepressant药物具有相似的化学方法e and biological effects. Scientists believe that patients with depression may have an imbalance in neurotransmitters, chemicals that nerves make and use to communicate with other nerves.

Tricyclicantidepressantsincrease levels of去甲肾上腺素andserotonin, two neurotransmitters, and block the action ofacetylcholine, anotherneurotransmitter. Scientists believe that by restoring the balance in these neurotransmitters in the brain that tricyclic antidepressants alleviate depression. In addition to relieving depression, tricyclic antidepressants also cause sedation and somewhat block effects ofhistamine.

Tricyclic antidepressants are approved by the Food and Drug Administration (FDA) for treating several types of depression, obsessive compulsive disorder, and bedwetting.

In addition, they are used for several off-label (non-FDA approved) uses such as:

• panic disorder,
• bulimia,
• chronic pain (for example,migraine, tension headaches, diabeticneuropathy, and post herpeticneuralgia),
• phantom limb pain,
• chronic itching, and
• premenstrualsymptoms.

Tricyclic antidepressants differ in their relative effects on serotonin, norepinephrine, and acetylcholine. The differences are reflected in how the tricyclic antidepressants are used and, most importantly, their propensity to cause certain side effects. For instance,amitriptyline(Elavil) causes more sedation,dry mouth, and constipation than other tricyclic antidepressants.

Tricyclic antidepressants may cause:

• blurred vision,
• dry mouth,
• constipation,
• weight gain or loss,
• low blood pressureon standing,
• rash,
• hives, and
• increased heart rate.

Tricyclic antidepressants should be used cautiously in patients with seizures since they can increase the risk of seizures.

Tricyclic antidepressants may worsen urinary retention (difficulty urinating) and narrow angleglaucoma. Abnormal heart rhythms and sexual dysfunction have also been associated with tricyclic antidepressants.

If tricyclic antidepressants are discontinued abruptly, withdrawal symptoms (for example, dizziness, headache, nausea, and restlessness) may occur.Withdrawal symptomsmay occur when even a few doses are missed. Therefore, the dose of antidepressant should be reduced gradually when therapy is discontinued.

Antidepressants increased the risk of suicidal thinking and behavior in short-term studies in children and adolescents with depression and other psychiatric disorders. Anyone considering the use of any antidepressant in a child or adolescent must balance this risk with the clinical need. Patients who are started on therapy should be closely observed for clinical worsening, suicidal thinking or behavior, and unusual changes in behavior.

Tricyclic antidepressants should not be used with monoamine oxidase inhibiting drugs [for example, tranylcypromine (Parnate)]. High fever, convulsions, and even death can occur from such combinations.

Epinephrine(Primatene,Adrenalin,Ana-Kit,EpiPen,Marcaine) should not be used with tricyclic antidepressants, since together they can cause severehigh blood pressure.

Alcohol blocks the antidepressant action of tricyclic antidepressants but increases itssedativeeffect.

Cimetidine(Tagamet) can increase blood levels and side effects of tricyclic antidepressants.

Combining tricyclic antidepressants with drugs that block acetylcholine can stop bowel movements and paralyze the intestine (paralyticileus). Dangerous elevations in blood pressure may occur if TCA are combined withclonidine(Catapres,Catapres-TTS).

The following are approved TCAs in the U.S.:

• amitriptyline (Elavil),
• clomipramine(Anafranil),
• doxepin(Sinequan),
• imipramine (Tofranil),
• trimipramine (Surmontil),
• amoxapine(Amoxapine Tablets),
• desipramine(Norpramin),
• nortriptyline(Pamelor, Aventyl), and
• protriptyline (Vivactil).