Amitriptyline

Absorption

Rapidly absorbed following oral administration (bioavailability is 30-60% due to first pass metabolism). Peak plasma concentrations are reached 2-12 hours after oral or intramuscular administration . Steady-state plasma concentrations vary greatly and this variation may be due to genetic differences .

Toxicity

Toxicity Data: Oral TDLO (child): 4167 μg/kg; Oral TDLO (man): 714 μg/kg/1D (intermittent); Oral TDLO (woman): 10 mg/kg .
Ingestion of 750 mg or more by an adult may result in severe toxicity. The effects in overdose are further increased by simultaneous ingestion of alcohol and another psychotropic agent . 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, among others , .
Use in pregnancy
For amitriptyline, only limited clinical data are available regarding its use in pregnancy. Amitriptyline is not recommended during pregnancy unless clearly required and only after careful consideration of both risks and benefits .
Use in breastfeeding
Amitriptyline and its metabolites are excreted into breast milk (corresponding to 0.6 % - 1 % of the maternal dose). A risk to the suckling child must be considered. A decision should be made as to whether it is appropriate to discontinue breastfeeding or to discontinue/abstain from the therapy of this medicinal product, considering the benefit of breastfeeding for the child and the benefit of therapy for the woman.
Effects on fertility
Animal studies have shown reproductive toxicity. No data on the effects of amitriptyline on human fertility are available .
Mutagenesis and carcinogenesis
The genotoxic potential of amitriptyline has been investigated in various in vitro and in vivo studies. Although these investigations showed some contradictory results, a potential of amitriptyline to lead to chromosome abnormalities cannot be excluded. Long-term carcinogenicity studies have not been performed to this date .

Originator

Elavil HCl Merck Sharp and,Dohme,US,1961

The Uses of Amitriptyline

Amitriptyline is used for anxious-depressive conditions. It is easier to tolerate than imipramine.

The Uses of Amitriptyline

Antidepressant.

Indications

This drug in indicated for the following conditions :
Major depressive disorder in adults
Management of neuropathic pain in adults
Prophylactic treatment of chronic tension-type headache (CTTH) in adults
Prophylactic treatment of migraine in adults
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 product should only be prescribed by a healthcare professional with expertise in the management of persistent enuresis
Off-label uses: irritable bowel syndrome, sleep disorders, diabetic neuropathy, agitation, fibromyalgia, and insomnia

Background

Amitriptyline is a tricyclic antidepressant that has been used to treat depression for decades. ELAVIL, a previously approved branded product of amitriptyline, was first approved by the FDA in 1961. Amitriptyline has been investigated in the treatment of pain-related conditions, attributed to its analgesic properties.

Definition

ChEBI: An organic tricyclic compound that is 10,11-dihydro-5H-dibenzo[a,d][7]annulene substituted by a 3-(dimethylamino)propylidene group at position 5.

Manufacturing Process

Phthalic anhydride is reacted with phenylacetic acid to form 3- benzylidenephthalide which is then hydrogenated to 2-phenethylbenzoic acid. Conversion to the acid chloride followed by intramolecular dehydrochlorination yields the ketone, 5H-dibenzo[a,d]cyclohepten-5-one. The ketone undergoes a Grignard reaction with 3-(dimethylamino)propyl chloride to give 5-(γ- dimethylaminopropylidene)-5H-dibenzo[a,d]cycloheptene.
Then, as described in US Patent 3,205,264, a solution of 5-(γ- dimethylaminopropylidene)-5H-dibenzo[a,d]cycloheptene (42 grams; 0.153 mol) in 105 ml of ethanol is hydrogenated over Raney nickel (1.5 grams) at 65°C under an initial hydrogen pressure of 450 lb. After 1 mol of hydrogen is absorbed (3.5 hours), the reaction mixture is filtered to remove the catalyst and is acidified with 80 ml of 2.5 N hydrochloric acid (0.2 mol). The acidic solution is concentrated to dryness under vacuum and is flushed three times with 100 ml of benzene to remove residual water. The solid residue then is dried under vacuum at 40°C to yield 44.9 grams (94% of theory) of the product, MP 187-189.5°C, equivalent weight 307, ultraviolet absorption A% 2380432. Recrystallization from isopropyl alcohol and ether affords the product in high purity.
In practice it is usually used as hydrochloride.

brand name

Elavil (AstraZeneca); Endep (Roche);Ami-anelun;Amilent;Amilit-ifi;Aminiurin;Amitimid;Amitriptol;Amyline;Amyzol;Annolytin;Apo-amitriptylline;Apo-pram;Deprelio;Deprestal;Diapatal;Elatrolet;Elavil plus;Emitrip;Enovil;Entrafon-210;Entrafon-2-10;Entrafon-2-25;Entrafon-a;Entrafon-forte;Etarfon;Etrafon-a;Etrafon-forte;Laroxal;Larozyl;Levate;Limbatarail;Limbatral;Limbitryl;Limitrol;Longopax;Loxaryl;Mareline;Meravil;Muaban d;Mutaban a/d/f;Nobrital;Novotriptyn;Novotryptin;Novo-tryptin;Parks-plus;Pms levazine;Prouvil;Saratem;Sarotena;Sedans;Sylvemid;Tensorelax;Teperin;Trepiline;Trepulin;Triptizol;Triptonal;Triptpane;Trivial-4-10.

Therapeutic Function

Antidepressant

World Health Organization (WHO)

Amitriptyline, a tricyclic antidepressant was introduced in 1961 for the management of endogenous depression and is listed in the 8th WHO Model List of Essential Drugs. Much of the adverse effects are caused by its antimuscarinic actions. These include dry mouth, cardiac arrhythmias, central nervous system disturbances, blood disorders and risk of suicide. The risk of suicide and dangers related to overdosage led the Norwegian Medicines Control Authority to put the higher strength formulation under prescribing restriction in 1992. The risk of death following overdosage is apparently higher for products containing tricyclic compounds as compared with nontricyclic products.

Biological Functions

Amitriptyline is a tertiary amine dibenzocycloheptadiene TCA with a propylidene side chain extending from the central carbocyclic ring. The diarylpropylideneamine moiety for amitriptyline makes it sensitive to photo-oxidation; therefore, its hydrochloride solutions should be protected from light to avoid ketone formation and precipitation.

Pharmacokinetics

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 .

Pharmacokinetics

Amitriptyline is rapidly absorbed from the GI tract and from parenteral sites.Amitriptyline and its active metabolite, nortriptyline, are distributed into breast milk. Amitriptyline is primarily (65%) metabolized by N-demethylation by CYP2D6 to nortriptyline and hydroxylation to its E-10-hydroxy metabolite. Nortriptyline is pharmacologically active as a secondary amine TCA. Amitriptyline shows approximately equal affinity for 5-HT and NE transporters.

Synthesis

Amitriptyline, 5-(3-dimethylaminopropyliden)-10,11-dihydrodibenzocycloheptene (7.1.4), differs from imipramine in that the nitrogen atom in the central part of the tricyclic system is replaced by a carbon, which is bound to a side chain by a double bond. Amitriptyline (7.1.4) is synthesized by interaction of 10,11-dihydro-N,N-dimethyl- 5H-dibenzo[a,d]cyclohepten-5-one with 3-dimethylaminopropylmagnesium bromide and the subsequent dehydration of the resulting tertiary alcohol (7.1.3) using hydrochloric acid [6–11].

An alternative way of synthesis of amitriptyline is by interaction of 10,11-dihydro-N,Ndimethyl-5H-dibenzo[a,d]-cyclohepten-5-one with cyclopropylmagnesium bromide, giving 10,11-dihydro-N,N-dimethyl-5H-dibenzo[a,d]-cyclohepten-5-cyclopropyl-5-ol (7.1.5). Reacting this with hydrogen bromide in acetic acid results in an opening of the cyclopropyl ring, which forms 5-(3-bromopropyliden)-10,11-dihydro-5H-dibenzo[a,d]-cycloheptene (7.1.6). Alkylating this with dimethylamine gives amitriptyline (7.1.4) [12,13].

Metabolism

In vitro, the metabolism of amitriptyline occurs mainly by demethylation (CYP2C19, CYP3A4) as well as hydroxylation (CYP2D6) followed by conjugation with glucuronic acid. Other isozymes involved in amitriptyline metabolism are CYP1A2 and CYP2C9. The metabolism of this drug is subject to genetic polymorphisms. The main active metabolite is the secondary amine, nortriptyline .
Nortriptyline is a stronger inhibitor of noradrenaline than of serotonin uptake, while amitriptyline inhibits the uptake of noradrenaline and serotonin with equal efficacy. Other metabolites such as cis- and trans-10-hydroxyamitriptyline and cis- and trans-10-hydroxynortriptyline have the same pharmacologic profile as nortriptyline but are significantly weaker. Demethylnortriptyline and amitriptyline N oxide are only present in plasma in negligible amounts; the latter is mostly inactive .