O-TRYPTYLINE

Indications

• Major depressive disorder
• Anxiety disorders
• Chronic pain syndromes
• Post-herpetic neuralgia
• Diabetic neuropathic pain
• Fibromyalgia (off-label use)

Dosage

Adults: The usual starting dose for adults is 75 mg daily, which can be adjusted based on response and tolerability, up to a maximum of 150 mg daily. For chronic pain, lower doses may be effective.

Mechanism of action

Amitriptyline inhibits the membrane pump mechanism responsible for the re-uptake of neurotransmitters like norepinephrine and serotonin, thereby increasing their concentrations at synaptic clefts in the brain. This action addresses deficiencies in neurotransmission that are linked to depressive symptoms. Its analgesic effects may stem from both its mood-altering properties and additional pharmacological actions.

Pharmacodynamics

Amitriptyline exhibits anticholinergic and sedative properties. It has demonstrated efficacy in managing conditions such as post-herpetic neuralgia and diabetic neuropathic pain, with clinical studies showing a good to moderate response in a significant proportion of patients. The drug may also influence cardiovascular function, potentially leading to ECG changes and increasing the risk of cardiac arrhythmias due to its effects on ion channels essential for cardiac repolarization.

Pharmacokinetics

Amitriptyline is well absorbed after oral administration and undergoes extensive first-pass metabolism, primarily by the liver. It has a high volume of distribution and is highly protein-bound. The half-life of amitriptyline varies considerably among patients, typically ranging from 10 to 50 hours. The drug's metabolites, including nortriptyline, also contribute to its therapeutic effects.

Contra-indications

• Hypersensitivity to amitriptyline or any of its components
• Acute recovery phase after myocardial infarction
• Concurrent use with monoamine oxidase inhibitors (MAOIs)

Adverse effects

• Drowsiness
• Dry mouth
• Constipation
• Blurred vision
• Weight gain
• Cardiac arrhythmias
• Orthostatic hypotension

Interactions

• Increased sedation with alcohol or other central nervous system depressants
• Increased risk of toxicity with other tricyclic antidepressants or drugs that affect serotonergic neurotransmission
• Potentially increased plasma levels of amitriptyline with drugs that inhibit CYP2D6

Precautions

• Caution in patients with a history of cardiovascular disease
• Use with caution in the elderly, due to increased risk of side effects
• Monitor for signs of serotonin syndrome when used with other serotonergic agents

Pregnancy

Amitriptyline should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

Amitriptyline is excreted in breast milk. Caution is advised when administering to nursing mothers.

Storage

Store in a cool, dry place away from light. Keep out of reach of children.

Formulations

• Tablets
• Oral solution

Mechanism of action

The mechanism of action of this drug is not fully elucidated. It is suggested that amitriptyline inhibits the membrane pump mechanism responsible for the re-uptake of transmitter amines, such as norepinephrine and serotonin, thereby increasing their concentration at the synaptic clefts of the brain,. These amines are important in regulating mood. The monoamine hypothesis in depression, one of the oldest hypotheses, postulates that deficiencies of serotonin (5-HT) and/or norepinephrine (NE) neurotransmission in the brain lead to depressive effects. This drug counteracts these mechanisms, and this may be the mechanism of amitriptyline in improving depressive symptoms. Whether its analgesic effects are related to its mood-altering activities or attributable to a different, less obvious pharmacological action (or a combination of both) is unknown. Acute and chronic effects of the antidepressant drugs tranylcypromine, a monoamine oxidase inhibitor, and amitriptyline, a monoamine uptake inhibitor, were studied on beta-adrenergic receptor function in mouse astrocytes in primary cultures. In clinically relevant concentrations, acute administration of either antidepressant drug had a direct inhibitory effect on the binding of the beta-adrenergic ligand dihydroalprenolol and on the isoproterenol-induced accumulation of cyclic AMP. However, in the absence of isoproterenol, these drugs enhanced the formation of cyclic AMP in the astrocytes. Chronic exposure to amitriptyline or tranylcypromine led to a decrease in isoproterenol-induced accumulation of cyclic AMP, and the time course for the development of this phenomenon was similar to that reported for whole brain in vivo. These findings suggest that these antidepressant drugs act as a partial agonists at beta-adrenergic receptors on astrocytes, and that the down-regulation of beta-adrenergic activity that occurs in vivo after chronic administration of antidepressant drugs may, to a large extent, take place in astrocytes and may result from the partial beta-agonist nature of the drugs. Astrocytes play important roles in guiding the construction of the nervous system, controlling extracellular ions and neurotransmitters, and regulating CNS synaptogenesis. Egr-1 is a transcription factor involved in neuronal differentiation and astrocyte cell proliferation. In this study, we investigated whether the tricyclic antidepressant (TCA) amitriptyline induces Egr-1 expression in astrocytes using rat C6 glioma cells as a model. We found that amitriptyline increased the expression of Egr-1 in a dose- and time-dependent manner. The amitriptyline-induced Egr-1 expression was mediated through serum response elements (SREs) in the Egr-1 promoter. SREs were activated by the Ets-domain transcription factor Elk-1 through the ERK and JNK mitogen-activated protein (MAP) kinase pathways. The inhibition of the ERK and JNK MAP kinase signals attenuated amitriptyline-induced transactivation of Gal4-Elk-1 and Egr-1 promoter activity. Our findings suggest that the induction of Egr-1 expression in astrocytes may be required to attain the therapeutic effects of antidepressant drugs. Antidepressants such as serotonin-noradrenaline reuptake inhibitors (SNRIs) and tricyclic antidepressants (TCAs) are frequently used for the management of neuropathic pain. Noradrenaline (NA) and serotonin (5-HT) increase in the spinal cord by reuptake inhibition is considered to be main mechanism of the therapeutic effect of antidepressants in neuropathic pain. In the present study, we examined the analgesic effects of duloxetine (SNRI) and amitriptyline (TCA) in a rat model of neuropathic pain induced by spinal nerve ligation (SNL). Intraperitoneal administration of duloxetine and amitriptyline dose-dependently (3,10 and 30 mg/kg) suppressed hyperalgesia induced by SNL. In vivo microdialysis in the lumbar spinal dorsal horn revealed that NA and 5-HT concentrations increased after intraperitoneal administration of duloxetine and am

Pharmacodynamics

**Effects in pain and depression** Amitriptyline is a tricyclic antidepressant and an analgesic. It has anticholinergic and sedative properties. Clinical studies have shown that oral amitriptyline achieves, at a minimum, good to moderate response in up to 2/3 of patients diagnosed with post-herpetic neuralgia and 3/4 of patients diagnosed with diabetic neuropathic pain, and neurogenic pain syndromes that are frequently unresponsive to narcotic analgesics. Amitriptyline has also shown efficacy in diverse groups of patients with chronic non-malignant pain. There have also been some studies showing efficacy in managing fibromyalgia (an off-label use of this drug),. **Cardiovascular and Anticholinergic Effects** Amitriptyline has strong anticholinergic properties and may cause ECG changes and quinidine-like effects on the heart. Amitriptyline may inhibit ion channels, which are necessary for cardiac repolarization (hERG channels), in the upper micromolar range of therapeutic plasma concentrations. Therefore, amitriptyline may increase the risk for cardiac arrhythmia. Orthostatic hypotension and tachycardia can be a problem in elderly patients receiving this drug at normal doses for depression. There is evidence in the literature that these effects may occur, rarely, at the lower dosages utilized in the treatment of pain. As with any other tricyclic antidepressant agent, increased glucose levels can occur with amitriptyline. **Effects on seizure threshold** This drug also decreases the convulsive threshold and causes alterations in EEG and sleep patterns.