TRIPTA TABLET 25mg

Amitriptyline

Source of information: Drugbank (External Link). Last updated on: 3rd July 18
*Trade Name used in the content below may not be the same as the HSA-registered product.

Active Ingredient / Synonyms

10,11-dihydro-5-(gamma-Dimethylaminopropylidene)-5H-dibenzo(a,D)cycloheptene | 10,11-dihydro-N,N-Dimethyl-5H-dibenzo(a,D)heptalene-delta(5),gamma-propylamine | 3-(10,11-dihydro-5H-Dibenzo(a,D)cyclohepten-5-ylidene)-N,N-dimethyl-1-propanamine | 3-(10,11-dihydro-5H-Dibenzo[a,D]cyclohepten-5-ylidene)-N,N-dimethylpropan-1-amine | 5-(3-Dimethylaminopropylidene)-10,11-dihydro-5H-dibenzo(a,D)cycloheptatriene | 5-(3-Dimethylaminopropylidene)-10,11-dihydro-5H-dibenzo(a,D)cycloheptene | 5-(gamma-Dimethylaminopropylidene)-5H-dibenzo[a,D][1,4]cycloheptadiene | Amitriptilina | Amitriptylin | Amitriptyline | Amitriptylinum | Amitriptyline |

Description

Amitriptyline hydrochloride is a dibenzocycloheptene-derivative tricyclic antidepressant (TCA) and analgesic. 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. Tertiary amine TCAs, such as amitriptyline, are more potent inhibitors of serotonin reuptake than secondary amine TCAs, such as nortriptyline. TCAs also down-regulate cerebral cortical β-adrenergic receptors and sensitize post-synaptic serotonergic receptors with chronic use. The antidepressant effects of TCAs are thought to be due to an overall increase in serotonergic neurotransmission. TCAs also block histamine-H1 receptors, α1-adrenergic receptors and muscarinic receptors, which accounts for their sedative, hypotensive and anticholinergic effects (e.g. blurred vision, dry mouth, constipation, urinary retention), respectively. Amitriptyline may be used to treat depression, chronic pain (unlabeled use), irritable bowel syndrome (unlabeled use), diabetic neuropathy (unlabeled use), post-traumatic stress disorder (unlabeled use), and for migraine prophylaxis (unlabeled use).

Indication

- 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, have 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

Mechanism of Action

Amitriptyline has anticholinergic and sedative properties. It 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 [FDA Label]. 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. There is some evidence in literature that neuronal and glial plasticity may be a critical action mediated by antidepressants via production of neurotrophic factors, such as GDNF, that promote neurogenesis, gliogenesis, development, plasticity, and survival [A31905]. In a study involving C6 glioma cells and normal human astrocytes, amitriptyline may activate the FGFR/FRS2α/ERK/CREB signaling cascade, thus resulting in GDNF production [A31905]. Amitriptyline displays affinity for muscarinic and histamine H1 receptors [FDA Label]. At both central and spinal cord level, amitriptyline exhibits ion-channel blocking effects on sodium, potassium and NMDA channel [FDA Label]. The noradrenaline, sodium and the NMDA effects are mechanisms known to be involved in the maintenance of neuropathic pain, chronic tension type headache prophylaxis and migraine prophylaxis [FDA Label]. In cultured rat cortical neurons, amitriptyline blocked sodium channel current (I(Na)) in a concentration-dependent, not voltage-dependent manner and reduced mRNA expression of sodium channels [A31906]. This may explain the actions of amitriptyline leading to migraine prophylaxis.

Pharmacodynamics

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, cardiovascular effects including orthostatic hypotension, changes in heart rhythm and conduction, and a lowering of the seizure threshold. As with other antidepressants, several weeks of therapy may be required in order to realize the full clinical benefit of amitriptyline. Although not a labelled indication, amitriptyline is widely used in the management of chronic nonmalignant pain (e.g., post-herpetic neuralgia, fibromyalgia).

Pharmacokinetics

Absorption:

Rapidly and well absorbed following oral administration (bioavailability is 30-60% due to first pass metabolism). Peak plasma concentrations occur 2-12 hours following oral or intramuscular administration. Amitriptyline and the main metabolite nortriptyline pass across the placental barrier and small amounts can be excreted with the breast milk [FDA Label].

Distribution:

The apparent volume of distribution (Vd)β estimated after intravenous administration is 1221 L±280 L; range 769-1702 L (16±3 L/kg) [FDA Label].

Metabolism:

Amitriptyline undergoes hepatic metabolism that mainly involves demethylation. Demethylation leads to the formation of its primary active metabolite, nortriptyline. This secondary amine retains a pharmacological activity. It can further undergo hydroxylation (mediated by CYP2D6) followed by conjugation with glucuronic acid. Other isozymes involved are CYP1A2 and CYP2C9. The metabolism is subject to genetic polymorphism [FDA Label]. Other metabolites such as cis- and trans-10-hydroxyamitriptyline and cis- and trans-10-hydroxynortriptyline have the same profile as nortriptyline but is considerably weaker.Demethylnortriptyline and amitriptyline N oxide are only present in plasma in minute amounts; the latter is almost inactive. All the metabolites are less anticholinergic than amitriptyline and nortriptyline. In plasma the amount of total 10-hydroxynortriptyline dominates but most of the metabolites are conjugated [FDA Label].

Elimination:

Amitriptyline and its metabolites are mainly excreted in the urine. Virtually the entire dose is excreted as glucuronide or sulfate conjugate of metabolites, with about 2% of unchanged drug appearing in the urine [FDA Label]. 25-50% of a single orally administered dose is excreted in urine as inactive metabolites within 24 hours. Small amounts are excreted in feces via biliary elimination.

Half-life

The elimination half-life (t1⁄2 β) amitriptyline after peroral administration is about 25 hours (24.65 ± 6.31 hours; range 16.49-40.36 hours) [FDA Label].

Clearance

The mean systemic clearance (Cls) is 39.24 ± 10.18 L/h, range 24.53-53.73 L/h [FDA Label].

Toxicity

LD50=350 mg/kg (in mice). Symptoms of overdose include abnormally low blood pressure, confusion, convulsions, dilated pupils and other eye problems, disturbed concentration, drowsiness, hallucinations, impaired heart function, rapid or irregular heartbeat, reduced body temperature, stupor, and unresponsiveness or coma. Side effects include: sedation, hypotension, blurred vision, dry mouth, constipation, urinary retention, postural hypotension, tachycardia, hypertension, ECG changes, heart failure, impaired memory and delirium, and precipitation of hypomanic or manic episodes in bipolar depression. Withdrawal symptoms include gastrointestinal disturbances, anxiety, and insomnia.

References

  1. Health Science Authority of Singapore - Reclassified POM
  2. Drugbank

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Approval Information

TRIPTA TABLET 25mg was registered with Health Science Authority of Singapore by ATLANTIC PHARMACEUTICAL (S) PTE LTD. It is marketed with the registration number of SIN00414P with effective from 1988-04-27.

This product contains 25mg of Amitriptyline in the form of TABLET, SUGAR-COATED.

The medicine was manufactured by ATLANTIC LABORATORIES CORPN LTD in THAILAND

It is a Presciption Only Medicine which can only be obtained from a doctor or a dentist, or from a pharmacist with a prescription from a Singapore-registered doctor or dentist.

Anatomical Therapeutic Chemical (ATC) Classification

ATC Code: N06AA09

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