The most common side effects are dry mouth, drowsiness, dizziness, constipation, and weight gain. Of note is sexual dysfunction, observed primarily in males. Glaucoma, liver toxicity and abnormal heart rhythms are rare but serious side effects. Blood levels of amitriptyline vary significantly from one person to another, and amitriptyline interacts with many other medications potentially aggravating its side effects.
Amitriptyline is effective for depression, but it is rarely used as a first-line antidepressant due to its higher toxicity in overdose and generally poorer tolerability. It can be tried for depression as a second-line therapy, after the failure of other treatments. For treatment-resistant adolescent depression or for cancer-related depression amitriptyline is no better than placebo. It is sometimes used for the treatment of depression in Parkinson disease, but supporting evidence for that is lacking.
Amitriptyline alleviates painful diabetic neuropathy. It is recommended by a variety of guidelines as a first or second line treatment. It is as effective for this indication as gabapentin or pregabalin but less well tolerated.
There is some (low-quality) evidence that amitriptyline may reduce pain in cancer patients. It is recommended only as a second line therapy for non-chemotherapy-induced neuropathic or mixed neuropathic pain, if opioids did not provide the desired effect.
Moderate evidence exists in favor of amitriptyline use for atypical facial pain. Amitriptyline is ineffective for HIV-associated neuropathy.
Amitriptyline is probably effective for the prevention of periodic migraine in adults. Amitriptyline is similar in efficacy to venlafaxine and topiramate but carries a higher burden of adverse effects than topiramate. For many patients, even very small doses of amitriptyline are helpful, which may allow for minimization of side effects. Amitriptyline is not significantly different from placebo when used for the prevention of migraine in children.
Amitriptyline may reduce the frequency and duration of chronic tension headache, but it is associated with worse adverse effects than mirtazapine. Overall, amitriptyline is recommended for tension headache prophylaxis, along with lifestyle advice, which should include avoidance of analgesia and caffeine.
Amitriptyline is effective for the treatment of irritable bowel syndrome; however, because of its side effects, it should be reserved for select patients for whom other agents do not work. There is insufficient evidence to support its use for abdominal pain in children with functional gastrointestinal disorders.
Amitriptyline may improve pain and urgency intensity associated with bladder pain syndrome and can be used in the management of this syndrome. Amitriptyline can be used in the treatment of nocturnal enuresis in children. However, its effect is not sustained after the treatment ends. Alarm therapy gives better short- and long-term results.
In the US, amitriptyline is commonly used in children with ADHD as an adjunct to stimulant medications without any evidence or guideline supporting this practice. Many physicians in the UK (and the US also) commonly prescribe amitriptyline for insomnia; however, Cochrane reviewers were not able to find any randomized controlled studies that would support or refute this practice.
Contraindications and precautions
The known contraindications of amitriptyline are:
CYP2D6 poor metabolizers should avoid amitriptyline due to increased side effects. If it is necessary to use it, half dose is recommended. Amitriptyline can be used during pregnancy and lactation, in the cases when SSRI do not work.
The most frequent side effects, occurring in 20% or more of users, are dry mouth, drowsiness, dizziness, constipation, and weight gain (on average 1.8 kg). Other common side effects (in 10% or more) are vision problems (amblyopia, blurred vision), tachycardia, increased appetite, tremor, fatigue/asthenia/feeling slowed down, and dyspepsia.
A literature review about abnormal movements and amitriptyline found that this drug is associated with various movement disorders, particularly dyskinesia, dystonia, and myoclonus. Stuttering and restless legs syndrome are some of the less common associations.
A less common side effect of amitriptyline is urination problems (8.7%).
Amitriptyline-associated sexual dysfunction (occurring at a frequency of 6.9%) seems to be mostly confined to males with depression and is expressed predominantly as erectile dysfunction and low libido disorder, with lesser frequency of ejaculatory and orgasmic problems. The rate of sexual dysfunction in males treated for indications other than depression and in females is not significantly different from placebo.
Liver tests abnormalities occur in 10-12% of patients on amitriptyline, but are usually mild, asymptomatic and transient, with consistently elevated alanine transaminase in 3% of all patients. The increases of the enzymes above the 3-fold threshold of liver toxicity are uncommon, and cases of clinically apparent liver toxicity are rare; nevertheless, amitriptyline is placed in the group of antidepressants with greater risks of hepatic toxicity.
The symptoms and the treatment of an overdose are largely the same as for the other TCAs, including the presentation of serotonin syndrome and adverse cardiac effects. The British National Formulary notes that amitriptyline can be particularly dangerous in overdose, thus it and other TCAs are no longer recommended as first-line therapy for depression.
The treatment of overdose is mostly supportive as no specific antidote for amitriptyline overdose is available. Activated charcoal may reduce absorption if given within 1–2 hours of ingestion. If the affected person is unconscious or has an impaired gag reflex, a nasogastric tube may be used to deliver the activated charcoal into the stomach. ECG monitoring for cardiac conduction abnormalities is essential and if one is found close monitoring of cardiac function is advised. Body temperature should be regulated with measures such as heating blankets if necessary. Cardiac monitoring is advised for at least five days after the overdose. Benzodiazepines are recommended to control seizures. Dialysis is of no use due to the high degree of protein binding with amitriptyline.
Since amitriptyline and its active metabolite nortriptyline are primarily metabolized by cytochromes CYP2D6 and CYP2C19 (see Amitriptyline#Pharmacology), the inhibitors of these enzymes are expected to exhibit pharmacokinetic interactions with amitriptyline. According to the prescribing information, the interaction with CYP2D6 inhibitors may increase the plasma level of amitriptyline. However, the results in the other literature are inconsistent: the co-administration of amitriptyline with a potent CYP2D6 inhibitor paroxetine does increase the plasma levels of amitriptyline two-fold and of the main active metabolite nortriptyline 1.5-fold, but combination with less potent CYP2D6 inhibitors thioridazine or levomepromazine does not affect the levels of amitriptyline and increases nortriptyline by about 1.5-fold; a moderate CYP2D6 inhibitor fluoxetine does not seem to have a significant effect on the levels of amitriptyline or nortriptyline. A case of clinically significant interaction with potent CYP2D6 inhibitor terbinafine has been reported.
A potent inhibitor of CYP2C19 and other cytochromes fluvoxamine increases the level of amitriptyline two-fold while slightly decreasing the level of nortriptyline. Similar changes occur with a moderate inhibitor of CYP2C19 and other cytochromes cimetidine: amitriptyline level increases by about 70%, while nortriptyline decreases by 50%.CYP3A4 inhibitor ketoconazole elevates amitriptyline level by about a quarter. On the other hand, cytochrome P450 inducers such as carbamazepine and St. John's Wort decrease the levels of both amitriptyline and nortriptyline
Oral contraceptives may increase the blood level of amitriptyline by as high as 90%. Valproate moderately increases the levels of amitriptyline and nortriptyline through an unclear mechanism.
The prescribing information warns that the combination of amitriptyline with monoamine oxidase inhibitors may cause potentially lethal serotonin syndrome; however, this has been disputed. The prescribing information cautions that some patients may experience a large increase in amitriptyline concentration in the presence of topiramate. However, other literature states that there is little or no interaction: in a pharmacokinetic study topiramate only increased the level of amitriptyline by 20% and nortriptyline by 33%.
Inhibition of serotonin and norepinephrine transporters by amitriptyline results in interference with neuronal reuptake of serotonin and norepinephrine. Since the reuptake process is important physiologically in terminating transmitting activity, this action may potentiate or prolong activity of serotonergic and adrenergic neurons and is believed to underlie the antidepressant activity of amitriptyline.
Inhibition of norepinephrine reuptake leading to increased concentration of norepinephrine in the
posterior grey column of the spinal cord appears to be mostly responsible for the analgesic action of amitriptyline. Increased level of norepinephrine increases the basal activity of alpha-2 adrenergic receptors, which mediate an analgesic effect by increasing gamma-aminobutyric acid transmission among spinal interneurons. The blocking effect of amitriptyline on sodium channels may also contribute to its efficacy in pain conditions.
Amitriptyline is readily absorbed from the gastrointestinal tract (90-95%). Absorption is gradual with the peak concentration in blood plasma reached after about 4 hours. Extensive metabolism on the first pass through the liver leads to average bioavailability of about 50% (45%-53%). Amitriptyline is metabolized mostly by CYP2C19 into nortriptyline and by CYP2D6 leading to a variety of hydroxylated metabolites, with the principal one among them being (E)-10-hydroxynortriptyline (see metabolism scheme), and to a lesser degree, by CYP3A4.
Metabolism of amitriptyline to major active metabolites.
Nortriptyline, the main active metabolite of amitriptyline, is an antidepressant on its own right. Nortriptyline reaches 10% higher level in the blood plasma than the parent drug amitriptyline and 40% greater area under the curve, and its action is an important part of the overall action of amitriptyline.
Another active metabolite is (E)-10-hydroxynortriptyline, which is a norepinephrine uptake inhibitor four times weaker than nortriptyline. (E)-10-hydroxynortiptyline blood level is comparable to that of nortriptyline, but its cerebrospinal fluid level, which is a close proxy of the brain concentration of a drug, is twice higher than nortriptyline's. Based on this, (E)-10-hydroxynortriptyline was suggested to significantly contribute to antidepressant effects of amitriptyline.
Blood levels of amitriptyline and nortriptyline and pharmacokinetics of amitriptyline in general, with clearance difference of up to 10-fold, vary widely between individuals. Variability of the area under the curve in steady state is also high, which makes a slow upward titration of the dose necessary.
In the blood, amitriptyline is 96% bound to plasma proteins; nortriptyline is 93–95% bound, and (E)-10-hydroxynortiptyline is about 60% bound.
Amitriptyline has an elimination half life of 21 hours, nortriptyline - 23–31 hours, and (E)-10-hydroxynortiptyline - 8–10 hours. Within 48 hours, 12-80% of amitriptyline is eliminated in the urine, mostly as metabolites. 2% of the unchanged drug is excreted in the urine. Elimination in the feces, apparently, have not been studied.
Therapeutic levels of amitriptyline range from 75 to 175 ng/mL (270–631 nM), or 80–250 ng/mL of both amitriptyline and its metabolite nortriptyline.
Since amitriptyline is primarily metabolized by CYP2D6 and CYP2C19, genetic variations within the genes coding for these enzymes can affect its metabolism, leading to changes in the concentrations of the drug in the body. Increased concentrations of amitriptyline may increase the risk for side effects, including anticholinergic and nervous system adverse effects, while decreased concentrations may reduce the drug's efficacy.
Individuals can be categorized into different types of CYP2D6 or CYP2C19 metabolizers depending on which genetic variations they carry. These metabolizer types include poor, intermediate, extensive, and ultrarapid metabolizers. Most individuals (about 77–92%) are extensive metabolizers, and have "normal" metabolism of amitriptyline. Poor and intermediate metabolizers have reduced metabolism of the drug as compared to extensive metabolizers; patients with these metabolizer types may have an increased probability of experiencing side effects. Ultrarapid metabolizers use amitriptyline much faster than extensive metabolizers; patients with this metabolizer type may have a greater chance of experiencing pharmacological failure.
The Clinical Pharmacogenetics Implementation Consortium recommends avoiding amitriptyline in patients who are CYP2D6 ultrarapid or poor metabolizers, due to the risk for a lack of efficacy and side effects, respectively. The consortium also recommends considering an alternative drug not metabolized by CYP2C19 in patients who are CYP2C19 ultrarapid metabolizers. A reduction in starting dose is recommended for patients who are CYP2D6 intermediate metabolizers and CYP2C19 poor metabolizers. If use of amitriptyline is warranted, therapeutic drug monitoring is recommended to guide dose adjustments. The Dutch Pharmacogenetics Working Group also recommends selecting an alternative drug or monitoring plasma concentrations of amitriptyline in patients who are CYP2D6 poor or ultrarapid metabolizers, and selecting an alternative drug or reducing initial dose in patients who are CYP2D6 intermediate metabolizers.
Chemical synthesis of amitriptyline.
Amitriptyline is a highly lipophilic molecule having an octanol-water partition coefficient (pH 7.4) of 3.0, while the log P of the free base was reported as 4.92. Solubility of the free base amitriptyline in water is 14 mg/L.
Amitriptyline is prepared by reacting benzosuberone with 3-(dimethylamino)propylmagnesium chloride and then heating the resulting intermediate product with hydrochloric acid to eliminate water.
Amitriptyline was first developed by the American pharmaceutical company Merck in the late 1950s. In 1958, Merck approached a number of clinical investigators proposing to conduct clinical trials of amitriptyline for schizophrenia. One of these researchers, Frank Ayd, instead, suggested using amitriptyline for depression. Ayd treated 130 patients and, in 1960, reported that amitriptyline had antidepressant properties similar to another, and the only known at the time, tricyclic antidepressant imipramine. Following this, the US Food and Drug Administration approved amitriptyline for depression in 1961.
In Europe, due to a quirk of the patent law at the time allowing patents only on the chemical synthesis but not on the drug itself, Roche and Lundbeck were able to independently develop and market amitriptyline in the early 1960s.
According to research by the historian of psychopharmacology David Healy, amitriptyline became a much bigger selling drug than its precursor imipramine because of two factors. First, amitriptyline has much stronger anxiolytic effect. Second, Merck conducted a marketing campaign raising clinicians' awareness of depression as a clinical entity.
Amitriptyline is the English and French generic name of the drug and its INN, BAN, and DCF, while amitriptyline hydrochloride is its USAN, USP, BANM, and JAN. Its generic name in Spanish and Italian and its DCIT are amitriptilina, in German is Amitriptylin, and in Latin is amitriptylinum. The embonate salt is known as amitriptyline embonate, which is its BANM, or as amitriptyline pamoate unofficially.
The few randomized controlled trials investigating amitriptyline efficacy in eating disorder have been discouraging.
^ abSchulz P, Balant-Gorgia AE, Kubli A, Gertsch-Genet C, Garrone G (1983). "Elimination and pharmacological effects following single oral doses of 50 and 75 mg of amitriptyline in man". Arch Psychiatr Nervenkr (1970). 233 (6): 449–55. doi:10.1007/BF00342785. PMID6667101. S2CID20844722.
^ abFangmann P, Assion HJ, Juckel G, González CA, López-Muñoz F (February 2008). "Half a century of antidepressant drugs: on the clinical introduction of monoamine oxidase inhibitors, tricyclics, and tetracyclics. Part II: tricyclics and tetracyclics". Journal of Clinical Psychopharmacology. 28 (1): 1–4. doi:10.1097/jcp.0b013e3181627b60. PMID18204333. S2CID31018835.
^Riblet N, Larson R, Watts BV, Holtzheimer P (2014). "Reevaluating the role of antidepressants in cancer-related depression: a systematic review and meta-analysis". Gen Hosp Psychiatry. 36 (5): 466–73. doi:10.1016/j.genhosppsych.2014.05.010. PMID24950919.
^ abSommer C, Alten R, Bär KJ, Bernateck M, Brückle W, Friedel E, Henningsen P, Petzke F, Tölle T, Üçeyler N, Winkelmann A, Häuser W (June 2017). "[Drug therapy of fibromyalgia syndrome : Updated guidelines 2017 and overview of systematic review articles]". Schmerz (in German). 31 (3): 274–284. doi:10.1007/s00482-017-0207-0. PMID28493231.
^van den Beuken-van Everdingen MH, de Graeff A, Jongen JL, Dijkstra D, Mostovaya I, Vissers KC (March 2017). "Pharmacological Treatment of Pain in Cancer Patients: The Role of Adjuvant Analgesics, a Systematic Review". Pain Pract. 17 (3): 409–419. doi:10.1111/papr.12459. PMID27207115. S2CID37418010.
^Do TM, Unis GD, Kattar N, Ananth A, McCoul ED (October 2020). "Neuromodulators for Atypical Facial Pain and Neuralgias: A Systematic Review and Meta-Analysis". Laryngoscope. 131 (6): 1235–1253. doi:10.1002/lary.29162. PMID33037835. S2CID222256076.
^Klein T, Woo TM, Panther S, Odom-Maryon T, Daratha K (2019). "Somnolence-Producing Agents: A 5-Year Study of Prescribing for Medicaid-Insured Children With Attention Deficit Hyperactivity Disorder". J Pediatr Health Care. 33 (3): e1–e8. doi:10.1016/j.pedhc.2018.10.002. PMID30630642. S2CID58577978.
^Hefner G, Hahn M, Hohner M, Roll SC, Klimke A, Hiemke C (January 2019). "QTc Time Correlates with Amitriptyline and Venlafaxine Serum Levels in Elderly Psychiatric Inpatients". Pharmacopsychiatry. 52 (1): 38–43. doi:10.1055/s-0044-102009. PMID29466824.
^Johne A, Schmider J, Brockmöller J, Stadelmann AM, Störmer E, Bauer S, Scholler G, Langheinrich M, Roots I (February 2002). "Decreased plasma levels of amitriptyline and its metabolites on comedication with an extract from St. John's wort ( Hypericum perforatum )". J Clin Psychopharmacol. 22 (1): 46–54. doi:10.1097/00004714-200202000-00008. PMID11799342. S2CID25670895.
^Berry-Bibee EN, Kim MJ, Simmons KB, Tepper NK, Riley HE, Pagano HP, Curtis KM (December 2016). "Drug interactions between hormonal contraceptives and psychotropic drugs: a systematic review". Contraception. 94 (6): 650–667. doi:10.1016/j.contraception.2016.07.011. PMID27444984.
^Roth BL, Driscol J. "PDSP Ki Database". Psychoactive Drug Screening Program (PDSP). University of North Carolina at Chapel Hill and the United States National Institute of Mental Health. Retrieved 14 August 2017.
^ abcTatsumi M, Groshan K, Blakely RD, Richelson E (1997). "Pharmacological profile of antidepressants and related compounds at human monoamine transporters". Eur. J. Pharmacol. 340 (2–3): 249–58. doi:10.1016/s0014-2999(97)01393-9. PMID9537821.
^ abcOwens MJ, Morgan WN, Plott SJ, Nemeroff CB (1997). "Neurotransmitter receptor and transporter binding profile of antidepressants and their metabolites". J. Pharmacol. Exp. Ther. 283 (3): 1305–22. PMID9400006.
^Hirst WD, Abrahamsen B, Blaney FE, Calver AR, Aloj L, Price GW, Medhurst AD (2003). "Differences in the central nervous system distribution and pharmacology of the mouse 5-hydroxytryptamine-6 receptor compared with rat and human receptors investigated by radioligand binding, site-directed mutagenesis, and molecular modeling". Mol. Pharmacol. 64 (6): 1295–308. doi:10.1124/mol.64.6.1295. PMID14645659. S2CID33743899.
^Monsma FJ, Shen Y, Ward RP, Hamblin MW, Sibley DR (1993). "Cloning and expression of a novel serotonin receptor with high affinity for tricyclic psychotropic drugs". Mol. Pharmacol. 43 (3): 320–7. PMID7680751.
^ abNojimoto FD, Mueller A, Hebeler-Barbosa F, Akinaga J, Lima V, Kiguti LR, Pupo AS (2010). "The tricyclic antidepressants amitriptyline, nortriptyline and imipramine are weak antagonists of human and rat alpha1B-adrenoceptors". Neuropharmacology. 59 (1–2): 49–57. doi:10.1016/j.neuropharm.2010.03.015. PMID20363235. S2CID207225294.
^ abcFallarero A, Pohjanoksa K, Wissel G, Parkkisenniemi-Kinnunen UM, Xhaard H, Scheinin M, Vuorela P (December 2012). "High-throughput screening with a miniaturized radioligand competition assay identifies new modulators of human α2-adrenoceptors". Eur J Pharm Sci. 47 (5): 941–51. doi:10.1016/j.ejps.2012.08.021. PMID22982401.
^Bylund DB, Snyder SH (1976). "Beta adrenergic receptor binding in membrane preparations from mammalian brain". Mol. Pharmacol. 12 (4): 568–80. PMID8699.
^ abcdefvon Coburg Y, Kottke T, Weizel L, Ligneau X, Stark H (2009). "Potential utility of histamine H3 receptor antagonist pharmacophore in antipsychotics". Bioorg. Med. Chem. Lett. 19 (2): 538–42. doi:10.1016/j.bmcl.2008.09.012. PMID19091563.
^ abcdAppl H, Holzammer T, Dove S, Haen E, Strasser A, Seifert R (February 2012). "Interactions of recombinant human histamine H1, H2, H3, and H4 receptors with 34 antidepressants and antipsychotics". Naunyn Schmiedebergs Arch. Pharmacol. 385 (2): 145–70. doi:10.1007/s00210-011-0704-0. PMID22033803. S2CID14274150.
^Ghoneim OM, Legere JA, Golbraikh A, Tropsha A, Booth RG (2006). "Novel ligands for the human histamine H1 receptor: synthesis, pharmacology, and comparative molecular field analysis studies of 2-dimethylamino-5-(6)-phenyl-1,2,3,4-tetrahydronaphthalenes". Bioorg. Med. Chem. 14 (19): 6640–58. doi:10.1016/j.bmc.2006.05.077. PMID16782354.
^ abcdeStanton T, Bolden-Watson C, Cusack B, Richelson E (1993). "Antagonism of the five cloned human muscarinic cholinergic receptors expressed in CHO-K1 cells by antidepressants and antihistaminics". Biochem. Pharmacol. 45 (11): 2352–4. doi:10.1016/0006-2952(93)90211-e. PMID8100134.
^ abcBymaster FP, Nelson DL, DeLapp NW, Falcone JF, Eckols K, Truex LL, Foreman MM, Lucaites VL, Calligaro DO (1999). "Antagonism by olanzapine of dopamine D1, serotonin2, muscarinic, histamine H1 and alpha 1-adrenergic receptors in vitro". Schizophr. Res. 37 (1): 107–22. doi:10.1016/s0920-9964(98)00146-7. PMID10227113. S2CID19891653.
^Werling LL, Keller A, Frank JG, Nuwayhid SJ (October 2007). "A comparison of the binding profiles of dextromethorphan, memantine, fluoxetine and amitriptyline: treatment of involuntary emotional expression disorder". Exp Neurol. 207 (2): 248–57. doi:10.1016/j.expneurol.2007.06.013. PMID17689532. S2CID38476281.
^Yamakawa Y, Furutani K, Inanobe A, Ohno Y, Kurachi Y (February 2012). "Pharmacophore modeling for hERG channel facilitation". Biochem Biophys Res Commun. 418 (1): 161–6. doi:10.1016/j.bbrc.2011.12.153. PMID22244872.
^Horishita T, Yanagihara N, Ueno S, Okura D, Horishita R, Minami T, Ogata Y, Sudo Y, Uezono Y, Sata T, Kawasaki T (December 2017). "Antidepressants inhibit Nav1.3, Nav1.7, and Nav1.8 neuronal voltage-gated sodium channels more potently than Nav1.2 and Nav1.6 channels expressed in Xenopus oocytes". Naunyn Schmiedebergs Arch Pharmacol. 390 (12): 1255–1270. doi:10.1007/s00210-017-1424-x. PMID28905186. S2CID23385313.
^The Pharmaceutical Codex. 1994. Principles and practice of pharmaceutics, 12th edn. Pharmaceutical press
^Hansch C, Leo A, Hoekman D. 1995. Exploring QSAR.Hydrophobic, electronic and steric constants. Washington, DC: American Chemical Society.
^Box KJ, Völgyi G, Baka E, Stuart M, Takács-Novák K, Comer JE (June 2006). "Equilibrium versus kinetic measurements of aqueous solubility, and the ability of compounds to supersaturate in solution--a validation study". J Pharm Sci. 95 (6): 1298–307. doi:10.1002/jps.20613. PMID16552741.
^ abHealy D (1997). The Antidepressant Era. Harvard University Press. pp. 74–76. ISBN0674039572.
^Press J (10 January 2021). "The Sopranos Fan's Guide to The Many Saints of Newark". Vanity Fair. Retrieved 10 January 2021. Livia is already troubled enough in the yesteryear of Many Saints that her doctor wants to prescribe her the antidepressant Elavil, but she rejects it. “I’m not a drug addict!” she sneers. Tony pores over the Elavil pamphlet with great interest and even schemes with Dickie Moltisanti to get his suffering mother to take it: “It could make her happy.”