Amitriptyline; Uses, Side Effects, Interactions, Pregnancy

Amitriptyline
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Amitriptyline is a derivative of dibenzocycloheptadiene and a tricyclic antidepressant. Amitriptyline inhibits the re-uptake of norepinephrine and serotonin by the presynaptic neuronal membrane in the central nervous system (CNS), thereby increasing the synaptic concentration of norepinephrine and serotonin. Due to constant stimulation to these receptors, amitriptyline may produce a downregulation of adrenergic and serotonin receptors, which may contribute to the antidepressant activity.

Amitriptyline hydrochloride is a medicine used to treat a number of mental illnesses. These include major depressive disorder and anxiety disorder, and less commonly attention deficit hyperactivity disorder and bipolar disorder. Other uses include prevention of migraines, treatment of neuropathic pain such as fibromyalgia and postherpetic neuralgia, and less commonly insomnia , its basically dibenzocycloheptene-derivative tricyclic antidepressant (TCA). TCAs are structurally similar to phenothiazines. They contain a tricyclic ring system with an alkyl amine substituent on the central ring. In non-depressed individuals, amitriptyline does not affect mood or arousal but may cause sedation. In depressed individuals, amitriptyline exerts a positive effect on mood. TCAs are potent inhibitors of serotonin and norepinephrine reuptake.

Mechanism of Action of Amitriptyline

Amitriptyline, a tertiary amine tricyclic antidepressant, is structurally related to both the skeletal muscle relaxant cyclobenzaprine and the thioxanthene antipsychotics such as thiothixene. It is extremely sedating, and thus improvement of sleep patterns can be the first benefit of treatment. Amitriptyline exhibits strong anticholinergic activity. Amitriptyline is metabolized to nortriptyline which inhibits the reuptake of norepinephrine and serotonin almost equally. Amitriptyline inhibits the membrane pump mechanism responsible for uptake of norepinephrine and serotonin in adrenergic and serotonergic neurons. Pharmacologically this action may potentiate or prolong neuronal activity since reuptake of these biogenic amines is important physiologically in terminating transmitting activity. This interference with the reuptake of norepinephrine and/or serotonin is believed by some to underlie the antidepressant activity of amitriptyline.

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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 AMPin the astrocytes. Chronic exposure to amitriptyline or tranylcypromine led to a decrease in the isoproterenol-induced accumulation of cyclic AMP, and the time course for the development of this phenomenon was similar to that reported for the whole brain in vivo. These findings suggest that these antidepressant drugs act as 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.

Indications of Amitriptyline

Indicated for the treatment of major depressive disorder in adults – Indicated for the management of neuropathic pain in adults – Indicated for the prophylactic treatment of chronic tension-type headache (CTTH) in adults – Indicated for the prophylactic treatment of migraine in adults – Indicated for the the treatment of nocturnal enuresis in children aged 6 years and above when organic pathology, including spina bifida and related disorders, has been excluded and no response has been achieved to all other non-drug and drug treatments, including antispasmodics and vasopressin-related products. This medicinal product should only be prescribed by a healthcare professional with expertise in the management of persistent enuresis. -Other off-label uses include irritable bowel syndrome, sleep disorders, diabetic neuropathy, agitation and insomnia

Contraindications of Amitriptyline

Dosages of Amitriptyline

Strengths: 10 mg; 25 mg;  50 mg; 75 mg; 100 mg;  150 mg;

Depression

Outpatients

  • Usual dose: 75 mg orally per day in divided doses; this may be increased to a total of 150 mg per day if needed
  • Alternate dose: 40 to 100 mg orally as a single dose at bedtime; this may be increased by 25 or 50 mg as needed at bedtime to a total of 150 mg per day
  • Maximum dose: 150 mg orally per day

Inpatients

  • Initial dose: 100 mg orally per day
  • Maintenance dose: 40 to 100 mg orally as a single dose at bedtime
  • Maximum dose: 300 mg orally per day

Geriatric Dose for Depression

  • 10 mg orally 3 times a day with 20 mg at bedtime

Pediatric Dose for Depression

12 years or older

  • 10 mg orally 3 times a day with 20 mg at bedtime

Neuropathic pain,tension headache, migraine

Adults

  • Recommended doses are 25 mg – 75 mg daily in the evening. Doses above 100 mg should be used with caution.
  • The initial dose should be 10 mg – 25 mg in the evening. Doses can be increased with 10 mg – 25 mg every 3 – 7 days as tolerated.
  • The dose can be taken once daily, or be divided into two doses. A single dose above 75 mg is not recommended.
  • The analgesic effect is normally seen after 2 – 4 weeks of dosing.
  • Elderly patients over 65 years of age and patients with cardiovascular disease
  • A starting dose of 10 mg – 25 mg in the evening is recommended.
  • Doses above 75 mg should be used with caution.

Neuropathic pain

Treatment is symptomatic and should, therefore, be continued for an appropriate length of time. In many patients, therapy may be needed for several years. Regular reassessment is recommended to confirm that the continuation of the treatment remains appropriate for the patient.

Prophylactic treatment of chronic tension-type headache and prophylactic treatment of migraine in adults

Treatment must be continued for an appropriate length of time. Regular reassessment is recommended to confirm that the continuation of the treatment remains appropriate for the patient.

Nocturnal enuresis

Pediatric population

The recommended doses for

  • Children aged 6 to 10 years: 10 mg – 20 mg. A suitable dosage form should be used for this age group.
  • Children aged 11 years and above: 25 mg – 50 mg daily
  • The dose should be increased gradually.
  • Dose to be administered 1-1½ hours before bedtime.
  • The maximum period of treatment course should not exceed 3 months. If repeated courses of

amitriptyline is needed, a medical review should be conducted every 3 months.

Postherpetic Neuralgia (Off-label)

  • 65-100 mg PO qDay for at least 3 weeks

Eating Disorder (Off-label)

  • 150 mg PO qHS for 8 weeks

Side Effects of Amitriptyline

The most common

Common 

Rare

Drug Interaction of Amitriptyline

Amitriptyline may interact with the following drugs, supplements, & may change the mode of action of drugs.

Pregnancy & Lactation of Amitriptyline

FDA Pregnancy Category C

Pregnancy

For amitriptyline, only limited clinical data are available regarding exposed pregnancies.

Animal studies have shown reproductive toxicity.

Amitriptyline is not recommended during pregnancy unless clearly necessary and only after careful consideration of the risk/benefit.

During chronic use and after administration in the final weeks of pregnancy, neonatal withdrawal symptoms can occur. This may include irritability, hypertonia, tremor, irregular breathing, poor drinking, and loud crying and possibly anticholinergic symptoms (urinary retention, constipation).

Lactation

Amitriptyline and its metabolites are excreted into breast milk (corresponding to 0.6 % – 1 % of the maternal dose). A risk to the suckling child cannot be excluded. A decision must be made whether to discontinue breastfeeding or to discontinue/abstain from the therapy of this medicinal product taking into account the benefit of breastfeeding for the child and the benefit of therapy for the woman.

References

 

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