Tricyclic Antidepressants

The tricyclic antidepressants, or TCAs, are one of the oldest and first types of antidepressant medications. Due to their many side effects, they are now second-line medications and usually only put into use when newer medications are not effective in controlling depression. They help improve mood and increase activity while reducing morbid feelings and restoring appetite and sleep.

Prototype and Other Medications

The prototype medication of the tricyclic antidepressant category of antidepressants is amitriptyline. Other TCAs that treat depression are imipramine, doxepin, nortriptyline, amoxapine, and trimipramine.

Expected Pharmacologic Action

TCAs help relieve major depression by blocking the reuptake of two neurotransmitters: norepinephrine and serotonin. While there is no firm cause of depression, it’s believed that the link is a deficiency of those two neurotransmitters. As you review the antidepressants in this lesson, you will notice that most of the medications in some way increase the availability of these transmitters. However, it’s also likely that other neurochemical alterations help generate the effects of TCAs because their therapeutic effects are not immediately evident. It takes several weeks for clients to feel the full therapeutic effect of antidepressant medications.

Adverse Drug Reactions

TCAs can cause a variety of adverse effects, the most common of which are drowsiness, sedation, orthostatic hypotension, and tachycardia. Anticholinergic effects such as dry mouth, constipation, urinary retention, and blurred vision are also possible. These medications can also increase the risk of suicide, especially in children and adolescents. Abrupt discontinuation can cause withdrawal, commonly manifesting as anxiety, headache, muscle pain, and nausea. There is also a high risk for overdose with TCAs, which can cause life-threatening dysrhythmias, confusion, and seizures.

Interventions

Monitor clients taking a TCA for sedation and dizziness and take safety measures to prevent falls. Monitor orthostatic vital signs by measuring a client’s blood pressure and pulse as they change from a lying position to sitting or standing. For significant drops in blood pressure or elevations in pulse, withhold medication and report your findings to the provider. Evaluate clients for increases in depression and suicidal ideation, and initiate suicide precautions when appropriate. When discontinuing the medication, taper the dosage over 2 weeks to prevent or minimize withdrawal. For overdose, prepare for gastric lavage, followed by activated charcoal and administer sodium bicarbonate to control dysrhythmias.

Safety Alert

An overdose of a tricyclic antidepressant can be fatal. It causes cardiotoxicity that can result in tachycardia, heart block, and ventricular fibrillation. It can also affect the CNS and cause anxiety, delirium, seizures, and coma. Due to the risk of fatal complications, clients are monitored frequently and only prescribed a limited supply at a time.

Administration

Give TCAs orally at bedtime. That way, the maximum sedative effects occur while the client is asleep or trying to sleep. TCAs have a sleep promotion benefit as well, plus any other adverse effects are minimal during waking hours. Expect the medication to take several weeks to exert its therapeutic effects and encourage clients to continue using the medication for 6 to 12 months to prevent relapse.

Client Instructions

Make sure that clients understand the need to take the medication at bedtime to prevent daytime drowsiness. Tell them not to drive or participate in activities that require mental alertness if they feel drowsy, and make sure they know to move slowly when changing from a lying position to sitting or standing. To minimize or counteract the medications’ anticholinergic effects, tell clients to urinate before taking the daily dose, to increase fiber and fluids, and to chew gum or suck on hard candy. Sipping water can also help. Make sure clients understand that they must be aware of and report any feelings of self-harm or worsening of depression. They should not stop taking the medication abruptly. They must continue medication therapy even if they feel better, and they must take the medication exactly as their provider prescribes.

Contraindications and Precautions

TCAs are contraindicated for clients with a previous allergy to TCAs, children younger than 12, for clients who recently had an acute myocardial infarction, for those who have cardiac dysrhythmias or a history of seizures, and for those who currently take MAOIs. Use these medications with caution for clients who have angle-closure glaucoma, prostatic hypertrophy, a history of urinary retention or electroconvulsive therapy, liver or renal disorders, suicidal ideation, schizophrenia, hematologic or respiratory disorders, diabetes mellitus, or alcoholism.

Interactions

TCAs interact with several medications, so providers need to be careful prescribing them for clients who are taking other prescription medications. CNS depressants increase sedation. Levodopa-carbidopa and sympathomimetic medications may increase the effects of those medications, such as hypertension. Administration within 2 weeks of MAOIs may cause hypertensive crisis. Cimetidine and methylphenidate increase amitriptyline levels. Anticholinergic medications such as antihistamines increase the anticholinergic effects of TCAs. Finally, the herbal supplements St. John’s wort, kava-kava, valerian, and chamomile can adversely affect the efficacy of amitriptyline.