- Tricyclic antidepressant
Tricyclic antidepressants (abbreviation TCAs) are a class of
antidepressantdrugs first used in the 1950s. They are named after the drugs' molecular structure, which contains three rings of atoms (compare tetracyclic antidepressant).
The first tricyclic antidepressant discovered was
imipramine, which was discovered accidentally in a search for a new antipsychoticin the late 1950s.
Antidepressant drugs in the tricyclic drug group (along with their actions as listed in
Note: Other sources suggest that most of the tricyclics combine adrenergic and serotonergic effects to some degree. This is often reported as selectivity ratios. Some of the above, in order from most selective for nor-epinephrine to most selective for serotonin: lofepramine, nortriptyline, amitriptyline, imipramine, clomipramine [Antidepressants and upper gastrointestinal bleeding, http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1116881, table at http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1116881&blobname=bmj_319_7217_1081__index.html] .
Tricyclics are sometimes classified as tertiary amines and secondary
amines. In general, the tertiary amines boost serotonin as well as nor-epinephrine (adrenergic) and produce more sedation, anticholinergic effects, and orthostatic hypotension. [ [http://www.emsvillage.com/articles/article.cfm?id=2099 Tricyclic Antidepressants: An Overview for EMS (Part 1 of 3) ] ] The secondary amines act primarily on nor-epinephrine and tend to have a lower side-effect profile [Managing Neuropathic Pain: New Approaches for Today's Clinical Practice, slide 37] .
Tertiary amines include: amitriptyline, imipramine, trimipramine, doxepin, clomipramine, and lofepramine.
Secondary amines include: nortriptyline, desipramine, protriptyline, and amoxapine.
Mechanism of action
mechanism of actionis not well understood, however it is generally thought that tricyclic antidepressants work by inhibiting the re-uptakeof the neurotransmitters norepinephrineand serotoninby neurons. Interestingly dopaminesystem is nearly spared of their action. Tricyclics may also possess an affinity for muscarinic and histamine H1 receptors to varying degrees. Although the pharmacologic effect occurs immediately, often the patient's symptoms do not respond for 2 to 4 weeks.cite book | editor = Sweetman SC | title =Martindale. The complete drug reference | edition = 33 | year = 2002 | publisher = Pharmaceutical Press | isbn = 0-85369-499-0] Although norepinephrineand dopamineare generally considered stimulatory neurotransmitters, tricyclic antidepressants also increase the effects H1 histamine, and thus most have sedativeeffects. [ [http://findarticles.com/p/articles/mi_m3225/is_3_71/ai_n11836585 Antidepressants and antiepileptic drugs for chronic non-cancer pain | American Family Physician | Find Articles at BNET.com ] ]
Chemistry of re-uptake inhibitors
The chemical action of re-uptake inhibitors in general was unknown for a long time. In August 2007, two research groups independently reported that the tricyclic molecule docks to the transporter protein in a cavity adjacent to where the neurotransmitter substrate binds, locking the substrate in place and thereby obstructing re-uptake transport. [ [http://www.rsc.org/chemistryworld/News/2007/August/09080702.asp Cheerful news for antidepressant research ] ]
Tricyclic antidepressants are used in numerous applications; mainly indicated for the treatment of
clinical depression, neuropathic pain, nocturnal enuresis, and ADHD, but they have also been used successfully for headache(including migraineheadache), anxiety, insomnia, smoking cessation, bulimia nervosa, irritable bowel syndrome, narcolepsy, pathological cryingor laughing, persistent hiccups, interstitial cystitis, and ciguaterapoisoning, and as an adjunct in schizophrenia.
For many years they were the first choice for pharmacological treatment of depression. Although still considered effective, they have been increasingly replaced by SSRIs and other newer drugs. A recent
Cochrane reviewof their effectiveness concluded that they were only slightly more effective than active placebos. [Moncrieff et al. (2003). [http://www.cochrane.org/reviews/en/ab003012.html Active placebos versus antidepressants for depression] . Cochrane databases.] Newer antidepressants are thought to have fewer side effects and are also thought to be less likely to result in death or serious injury if used in a suicideattempt, as the treatment and lethal doses (see therapeutic index) are farther apart than with the tricyclic antidepressants. Tricyclic antidepressants are sometimes still used to treat treatment-resistant depressionthat has failed to respond to standard SSRI therapy.cite journal | author = Broquet K | title = Status of treatment of depression | journal = South Med J | volume = 92 | issue = 9 | pages = 846–56 | year = 1999 | pmid = 10498158] They are not considered addictive and are preferable to the MAOIs. Side effects usually occur before depression is effectively suppressed; for this reason and via other mechanisms they can be dangerous, as volition may be increased, giving the patient greater ability to attempt suicide.cite journal | author = Teicher M, Glod C, Cole J | title = Antidepressant drugs and the emergence of suicidal tendencies | journal = Drug Saf | volume = 8 | issue = 3 | pages = 186–212 | year = 1993 | pmid = 8452661 | doi = 10.2165/00002018-199308030-00002 ]
Tricyclic antidepressants have been shown to be effective in treating
attention-deficit hyperactivity disorder.cite journal | author = Biederman J, Baldessarini R, Wright V, Knee D, Harmatz J | title = A double-blind placebo controlled study of desipramine in the treatment of ADD: I. Efficacy | journal = J Am Acad Child Adolesc Psychiatry | volume = 28 | issue = 5 | pages = 777–84 | year = 1989 | pmid = 2676967] ADHD is thought to be caused by dopamineand norepinephrineshortages in the brain's prefrontal cortex. Tricyclic antidepressants block the reuptake of these neurotransmitters.cite journal | author = Biederman J, Spencer T | title = Attention-deficit/hyperactivity disorder (ADHD) as a noradrenergic disorder | journal = Biol Psychiatry | volume = 46 | issue = 9 | pages = 1234–42 | year = 1999 | pmid = 10560028 | doi = 10.1016/S0006-3223(99)00192-4 ] They are commonly used in patients for whom psychostimulants (the primary medication for ADHD) are ineffective or contraindicted. TCAs are more effective in treating the behavioral aspects of ADHD than the cognitive deficits; they help limit hyperactivity and impulsivity but have little effect on attention.cite journal | author = Popper C | title = Antidepressants in the treatment of attention-deficit/hyperactivity disorder | journal = J Clin Psychiatry | volume = 58 | issue = Suppl 14 | pages = 14–29; discussion 30–1 | year = 1997 | pmid = 9418743]
Tricyclics are also known as effective
analgesicsfor different types of pain, especially neuropathic).cite journal | author = Micó J, Ardid D, Berrocoso E, Eschalier A | title = Antidepressants and pain | journal = Trends Pharmacol Sci | volume = 27 | issue = 7 | pages = 348–54 | year = 2006 | pmid = 16762426 | doi = 10.1016/j.tips.2006.05.004 ] cite journal | author = McQuay H, Tramèr M, Nye B, Carroll D, Wiffen P, Moore R | title = A systematic review of antidepressants in neuropathic pain | journal = Pain | volume = 68 | issue = 2-3 | pages = 217–27 | year = 1996 | pmid = 9121808 | doi = 10.1016/S0304-3959(96)03140-5 ] A precise mechanism for their analgesic action is unknown, but it is thought that they modulate opioidsystems in the CNS via an indirect serotonergic route.cite journal | author = Botney M, Fields H | title = Amitriptyline potentiates morphine analgesia by a direct action on the central nervous system | journal = Ann Neurol | volume = 13 | issue = 2 | pages = 160–4 | year = 1983 | pmid = 6219612 | doi = 10.1002/ana.410130209 ] They are also effective in migraineprophylaxis, but not in relief of an acute migraine attack. This is also believed to be related to serotonergic effects. There is, however, little evidence for an analgesic effect in acute pain.
Tricyclics with greater
anti-muscarinicaction (i.e., amitriptyline, imipramineand nortriptyline) may prove useful in helping to treat nocturnal enuresis(bedwetting) in children over the age of 7 years. The drug needs to be gradually withdrawn and the total treatment period is advised to be no greater than 3 months at a time. It is thought that the anticholinergic effects of tricyclics may inhibit urination, and/or the CNS stimulant effect may lead to easier arousal when the stimulus of a full bladder occurs.cite book | editor = McEvoy GK | title =AHFS drug information | year = 2005 | publisher = American Society of Health-System Pharmacists | isbn = 1-58528-117-4] However, one robust review of tricyclics for the treatment of enuresis found the benefits of tricyclics were relatively small and transient and due to potentially serious adverse effects suggested more research into other methods ( bedwetting alarms, behavioural methods, desmopressin) which may be better suited for treatment of this condition.cite journal | author = Glazener C, Evans J, Peto R | title = Tricyclic and related drugs for nocturnal enuresis in children | journal = Cochrane Database Syst Rev | volume = | issue =3 | pages = CD002117 | year = 2003| pmid = 12917922 | doi = 10.1002/14651858.CD002117]
Many side effects are related to tricyclics
antimuscarinicactions. The antimuscarinic side effects are relatively common and include:
* Dry mouth (salivary secretion is affected)
* Dry nose
* Blurred vision (accommodation in the eye is affected)
* Decreased gastro-intestinal motility and secretion. This may lead to
* Urinary retention or difficulty with urination
Tolerance to these adverse effects often develops if treatment is continued, side effects may also be less troublesome if treatment is initiated with low dose and then gradually increased, although this may delay the clinical effect.
Other side effects may include drowsiness,
anxiety, restlessness, cognitive and memorydifficulties, confusion, dizziness, akathisia, hypersensitivityreactions, increased appetite with weight gain, sweating, decrease in sexual ability and desire, muscletwitches, weakness, nausea and vomiting, hypotension, tachycardia, and rarely, irregular heart rhythms.Rhabdomyolysis or muscle breakdown has been rarely reported with this class of drugs. [http://www.occup-med.com/content/1/1/16]
TCAs are highly metabolized by the cytochrome P450 hepatic enzymes. Drugs that inhibit cytochrome P450 (for example
cimetidine, methylphenidate, antipsychotics, and calcium channel blockers) may produce decreases in the tricyclic's metabolism leading to increases in tricyclic blood concentrations and accompanying toxicity. Drugs which prolong the QT intervalincluding antiarrhythmics such as quinidine, the antihistamines astemizoleand terfenadine, and some antipsychotics may increase the chance of ventricular dysrhythmias. TCAs may enhance the response to alcoholand the effects of barbiturates and other CNS depressants. Side effects may also be enhanced by other drugs which have antimuscarinic properties.
Tricyclic antidepressant overdose is a significant cause of fatal drug
poisoning. The severe morbidityand mortality associated with these drugs is well documented due to their cardiovascular and neurological toxicity. Additionally, it is a serious problem in the pediatric population due to their inherent toxicitycite journal | author = Rosenbaum T, Kou M | title = Are one or two dangerous? Tricyclic antidepressant exposure in toddlers | journal = J Emerg Med | volume = 28 | issue = 2 | pages = 169–74 | year = 2005 | pmid = 15707813 | doi = 10.1016/j.jemermed.2004.08.018 ] and the availability of these in the home when prescribed for bed wetting and depression.
central nervous systemand heartare the two main systems that are affected. Initial or mild symptoms include drowsiness, a dry mouth, nausea, and vomiting. More severe complications include hypotension, cardiac rhythm disturbances, hallucinations, and seizures. Electrocardiogram(ECG) abnormalities are frequent and a wide variety of cardiac dysrhythmias can occur, the most common being sinus tachycardia and intraventricular conduction delay (QRS prolongation).cite journal | author = Thanacoody H, Thomas S | title = Tricyclic antidepressant poisoning : cardiovascular toxicity | journal = Toxicol Rev | volume = 24 | issue = 3 | pages = 205–14 | year = 2005 | pmid = 16390222 | doi = 10.2165/00139709-200524030-00013] Seizures and cardiac dysrhythmias are the most important life threatening complications.
Tricyclics have a narrow
therapeutic index, i.e. the therapeutic doseis close to the toxic dose. In the medical literature the lowest reported toxic dose is 6.7 mg per kg body weight, ingestions of 10 to 20 mg per kilogram of body weight are a risk for moderate to severe poisoning, although doses ranging from 1.5 to 5 mg/kg may even present a risk. Most poison control centers refer any case of TCA poisoning (especially in children) to a hospital for monitoring.cite journal | author = McFee R, Mofenson H, Caraccio T | title = A nationwide survey of the management of unintentional-low dose tricyclic antidepressant ingestions involving asymptomatic children: implications for the development of an evidence-based clinical guideline | journal = J Toxicol Clin Toxicol | volume = 38 | issue = 1 | pages = 15–9 | year = 2000 | pmid = 10696919 | doi = 10.1081/CLT-100100910] Factors that increase the risk of toxicity include advancing age, cardiac status, and concomitant use of other drugs.cite journal | author = Preskorn S, Irwin H | title = Toxicity of tricyclic antidepressants--kinetics, mechanism, intervention: a review | journal = J Clin Psychiatry | volume = 43 | issue = 4 | pages = 151–6 | year = 1982 | pmid = 7068546] However, serum drug levels are not useful for evaluating risk of arrhythmia or seizure in tricyclic overdose.cite journal | author = Boehnert M, Lovejoy F | title = Value of the QRS duration versus the serum drug level in predicting seizures and ventricular arrhythmias after an acute overdose of tricyclic antidepressants | journal = N Engl J Med | volume = 313 | issue = 8 | pages = 474–9 | year = 1985 | pmid = 4022081]
Most of the toxic effects of TCAs are caused by four major pharmacological effects. TCAs have
anticholinergiceffects, cause excessive blockade of norepinephrinereuptake at the postganglionic synapse, direct alpha adrenergic blockade, and importantly they block sodium membrane channels with slowing of membrane depolarization, thus having quinidinelike effects on the myocardium.cite journal | author = Kerr G, McGuffie A, Wilkie S | title = Tricyclic antidepressant overdose: a review | journal = Emerg Med J | volume = 18 | issue = 4 | pages = 236–41 | year = 2001 | pmid = 11435353 | doi = 10.1136/emj.18.4.236 ]
Initial treatment of an acute overdose includes gastric decontamination of the patient. This is achieved by administering
activated charcoalwhich adsorbsthe drug in the gastrointestinal tracteither orally or via a nasogastric tube. Other decontamination methods such as stomach pumps, ipecac induced emesis, or whole bowel irrigationare not recommended in TCA poisoning.cite journal | author = Teece S, Hogg K | title = Gastric lavage in tricyclic antidepressant overdose | journal = Emerg Med J | volume = 20 | issue = 1 | pages = 64 | year = 2003 | pmid = 12533375 | doi = 10.1136/emj.20.1.64 ] cite journal | author = Dargan P, Colbridge M, Jones A | title = The management of tricyclic antidepressant poisoning : the role of gut decontamination, extracorporeal procedures and fab antibody fragments | journal = Toxicol Rev | volume = 24 | issue = 3 | pages = 187–94 | year = 2005 | pmid = 16390220 | doi = 10.2165/00139709-200524030-00011]
Symptomatic patients are usually monitored in an intensive care unit for a minimum of 12 hours, with close attention paid to maintenance of the airways, along with monitoring of blood pressure, arterial pH, and continuous ECG monitoring. Supportive therapy is given if necessary, including respiratory assistance, maintenance of body temperature, and administration of
sodium bicarbonateas an antidote. Sodium bicarbonate is given intravenouslyand it has been shown to be an effective treatment for resolving the metabolic acidosisand cardiovascular complications of TCA poisoning. If sodium bicarbonate therapy fails to improve cardiac symptoms, conventional antidysrhythmic drugs such as phenytoinand magnesiumcan be used to reverse any cardiac abnormalities. However, no benefit has been shown from lidocaineor other class 1a and 1c antiarrhythmic drugs; it appears they worsen the sodium channel blockade, slow conduction velocity, and depress contractility and should be avoided in TCA poisoning.cite journal | author = Bradberry S, Thanacoody H, Watt B, Thomas S, Vale J | title = Management of the cardiovascular complications of tricyclic antidepressant poisoning : role of sodium bicarbonate | journal = Toxicol Rev | volume = 24 | issue = 3 | pages = 195–204 | year = 2005 | pmid = 16390221 | doi = 10.2165/00139709-200524030-00012 ] Hypotension is initially treated with fluids along with bicarbonate to reverse metabolic acidosis(if present), if the patient remains hypotensive despite fluids then further measures such as the administration of epinephrine, norepinephrine, or dopaminecan be used to increase blood pressure. Another potentially severe symptom is seizures; often seizures resolve without treatment but administration of a benzodiazepineor other anticonvulsive may be required for persistent muscular overactivity. There is no role for physostigminein the treatment of tricyclic toxicity as it may increase cardiac toxicity and cause seizures.
Tricyclic antidepressants are highly protein bound and have a large
volume of distribution; therefore removal of these compounds from the blood with hemodialysis, hemoperfusionor other techniques are unlikely to be of any significant benefit.
Studies in the 1990s in
Australiaand the United Kingdomshowed that between 8 and 12% of drug overdoses were following TCA ingestion. TCAs may be involved in up to 33% of all fatal poisonings, second only to analgesics.cite journal | author = Thomas S, Bevan L, Bhattacharyya S, Bramble M, Chew K, Connolly J, Dorani B, Han K, Horner J, Rodgers A, Sen B, Tesfayohannes B, Wynne H, Bateman D | title = Presentation of poisoned patients to accident and emergency departments in the north of England | journal = Hum Exp Toxicol | volume = 15 | issue = 6 | pages = 466–70 | year = 1996 | pmid = 8793528] cite journal | author = Buckley N, Whyte I, Dawson A, McManus P, Ferguson N | title = Self-poisoning in Newcastle, 1987-1992 | journal = Med J Aust | volume = 162 | issue = 4 | pages = 190–3 | year = 1995 | pmid = 7877540]
Tricyclic antidepressants were developed amid the "explosive birth" of psychopharmacology in the early 1950s. The story begins with the synthesis of
Chlorpromazinein December 1950 by Rhône-Poulenc's chief chemist, Paul Charpentier, from synthetic antihistaminesdeveloped by Rhône-Poulenc in the 1940s. [A Guide to the Extrapyramidal Side-Effects of Antipsychotic Drugs, D. G. Cunningham Owens, http://assets.cambridge.org/97805216/33536/excerpt/9780521633536_excerpt.pdf] Its psychiatric effects were first noticed at a hospital in Paris in 1952. The first widely-used psychiatric drug, by 1955 it was already generating significant revenue as an antipsychotic. [Becoming Neurochemical Selves, Nikolas Rose, p.3] Research chemists quickly began to explore other derivatives of chlorpromazine.
The first TCA reported for the treatment of depression was
imipramine, an imino-dibenzyl analogue of chlorpromazine code-named G22355. It was not originally targeted for the treatment of depression. The drug's tendency to induce manic effects was "later described as 'in some patients, quite disastrous'". The paradoxical observation of a sedative inducing mania lead to testing with depressed patients. The first trial of imipramine took place in 1955 and the first report of antidepressant effects was published by Swiss psychiatrist Ronald Kuhnin 1957. [A Guide to the Extrapyramidal Side-Effects of Antipsychotic Drugs, D. G. Cunningham Owens, http://assets.cambridge.org/97805216/33536/excerpt/9780521633536_excerpt.pdf] Some testing of Geigy’s imipramine, then known as Tofranil, took place at the Münsterlingen Hospitalnear Konstanz. [Becoming Neurochemical Selves, Nikolas Rose, p.3] Geigy later became Ciba-Geigy and eventually Novartis.
Many patents were filed in the 1950s and 1960s concerning variations on these three-ring structures with applications to psychiatric conditions.
Phenothiazinederivatives are described in U.S. patent 2,591,679 issued 1952-04-08to John W. Cusic. The compounds described contain a sulfur group on the central carbon ring, and a nitrogen atom in the cental ring to which the side chain attaches, in the manner of chlorpromazine. Most of the illustrated side chains contain an amine group.
Dibenzazepinederivatives are described in U.S. patent 3,074,931 issued 1963-01-22by assignment to Smith Kline & French Laboratories. The compounds described share a tricyclic backbone identical to the backbone of the TCA amitriptylineand family of side chains typical of early TCA drugs.
Merck introduced the second member of the TCA family, amitriptyline (Elavil), in 1961. [Becoming Neurochemical Selves, Nikolas Rose, p.3]
These patents cover the structures of the compounds and their mode of chemical synthesis. Understanding of their mode of action as re-uptake inhibitors and development of the serotonin theory of depression came in the years to follow.
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