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{{Infotaula fàrmac}}
La '''levotiroxina''', també coneguda com a '''{{small|L}}-thyroxine''', és una forma sintètica de l'[[hormona tiroïdal]] [[tiroxina]] (T<sub>4</sub>).<ref name="AHFS2016" /><ref name="King2010">{{cite book|last1=King|first1=Tekoa L.|last2=Brucker|first2=Mary C.|title=Pharmacology for Women's Health|date=2010|publisher=Jones & Bartlett Publishers|isbn=9781449658007|page=544|url=https://books.google.com/books?id=E9qVyrNPsBkC&pg=PA544|language=anglès|url-status=live|archive-url=https://web.archive.org/web/20170910234123/https://books.google.com/books?id=E9qVyrNPsBkC&pg=PA544|archive-date=10 September 2017|df=dmy-all}}</ref> S'empra per tractar la [[deficiència d'hormona tiroïdal]], incloent la forma més greu anomenada [[coma mixedematós]].<ref name="AHFS2016" /> També pot ser emprada per tractar i prevenir certs tipus de [[Tumor tiroïdal|tumors tiroïdals]].<ref name="AHFS2016" /> No està indicat per la [[pèrdua de pes]].<ref name="AHFS2016" /> Es pot prendre per via oral o [[Teràpia intravenosa|intravenosa]].<ref name="AHFS2016" /> El seu efecte màxim es produeix a les 6 setmanes de la dosi.<ref name="AHFS2016" />
== Indicacions clíniques ==
▲Side effects from excessive doses include weight loss, trouble tolerating heat, sweating, anxiety, trouble sleeping, [[tremor]], and [[fast heart rate]].<ref name=AHFS2016/> Use is not recommended in people who have had a recent [[myocardial infarction|heart attack]].<ref name=AHFS2016/> Use during [[pregnancy]] has been found to be safe.<ref name=AHFS2016/> It is recommended that dosing be based on regular measurements of [[thyroid-stimulating hormone]] (TSH) and T<sub>4</sub> levels in the blood.<ref name=AHFS2016/> Much of the effect of levothyroxine is following its conversion to [[triiodothyronine]] (T<sub>3</sub>).<ref name=AHFS2016>{{cite web|title=Levothyroxine Sodium|url=https://www.drugs.com/monograph/levothyroxine-sodium.html|publisher=The American Society of Health-System Pharmacists|access-date=8 December 2016|url-status=live|archive-url=https://web.archive.org/web/20161221013136/https://www.drugs.com/monograph/levothyroxine-sodium.html|archive-date=21 December 2016|df=dmy-all}}</ref>
Una altra utilitat de la levotiroxina és el tractament de l'hipotiroïdisme subclínic (nivells elevats de TSH amb nivells normals de T<sub>4</sub> lliure sense simptomatologia).<ref name="Gaitonde" /> La naturalesa assimptomàtica d'aquests pacients provoca que la necessitat del seu tractament generi controvèrsia.<ref name="Roberts" /> Un benefici de tractar aquesta població concreta amb levotiroxina és la prevenció d'hipotiroïdisme clínic<ref name="Roberts" /> En aquests casos, es recomana que es tingui en compte el tractament en aquells pacients amb nivells inicials de TSH per sobre de 10 mIU/L, en aquells pacients amb nivells elevats d'[[anticossos antitiroïdals]], en aquells pacients amb símptomes d'[[hipotiroïdisme]] i nivells de TSH en l'interval de 5–10 mIU/L i en dones [[Embaràs|embarassades]] o que han manifestat el seu desig de gestació.<ref name="Roberts" /> La dosificació oral per pacients amb hipotiroïdisme subclínic és d'1 μg/kg/dia.<ref name="LexiComp">{{Cite web|title=Levothyroxine (Lexi-Drugs)|work=LexiComp|url=http://online.lexi.com/lco/action/doc/retrieve/docid/patch_f/7172|access-date=20 April 2014|url-status=live|archive-url=https://web.archive.org/web/20140929172946/http://online.lexi.com/lco/action/doc/retrieve/docid/patch_f/7172|archive-date=29 September 2014|df=dmy-all}}</ref>
▲Levothyroxine is typically used to treat [[hypothyroidism]],<ref name="pmid18662921">{{cite journal | vauthors = Vaidya B, Pearce SH | title = Management of hypothyroidism in adults | journal = BMJ | volume = 337 | pages = a801 | date = July 2008 | pmid = 18662921 | doi = 10.1136/bmj.a801 }}</ref> and is the treatment of choice for people with hypothyroidism,<ref name=Roberts>{{cite journal |doi=10.1016/S0140-6736(04)15696-1 |title=Hypothyroidism |journal=The Lancet |volume=363 |issue=9411 |pages=793 |year=2004 |last1=Roberts |first1=Caroline GP |last2=Ladenson |first2=Paul W }}</ref> who often require lifelong thyroid hormone therapy.<ref name=Gaitonde>{{cite journal | vauthors = Gaitonde DY, Rowley KD, Sweeney LB | title = Hypothyroidism: an update | journal = American Family Physician | volume = 86 | issue = 3 | pages = 244–51 | date = August 2012 | pmid = 22962987 | url = http://www.aafp.org/link_out?pmid=22962987 }}</ref> Doses of levothyroxine that normalize serum TSH may not normalize LDL cholesterol and total cholesterol.<ref>{{cite journal |vauthors=McAninch EA, Rajan KB, Miller CH, Bianco AC |title=Systemic Thyroid Hormone Status During Levothyroxine Therapy In Hypothyroidism: A Systematic Review and Meta-Analysis |journal=J. Clin. Endocrinol. Metab. |volume= |issue= |pages= |date=August 2018 |pmid=30124904 |doi=10.1210/jc.2018-01361 |pmc=6226605}}</ref>
També és part del tractament del [[coma mixedematós]], una forma greu d'hipotiroïdisme caracteritzada per [[Alteració de l'estat de consciència|alteracions de l'estat de consciència]] i [[hipotèrmia]].<ref name="Gaitonde" /> Pel fet de ser una emergència mèdica amb una taxa elevada de [[Taxa de mortalitat|mortalitat]], hauria de ser tractada en una unitat de [[medicina intensiva]]<ref name="Gaitonde" /> amb teràpia de reemplaçament amb hormones tiroïdals i un maneig intensiu de les complicacions orgàniques que s'hagin pogut produir.<ref name="Roberts" />
▲It may also be used to treat [[goiter]] via its ability to lower [[thyroid-stimulating hormone]] (TSH), a hormone that is considered goiter-inducing.<ref name="pmid16507633">{{cite journal | vauthors = Svensson J, Ericsson UB, Nilsson P, Olsson C, Jonsson B, Lindberg B, Ivarsson SA | title = Levothyroxine treatment reduces thyroid size in children and adolescents with chronic autoimmune thyroiditis | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 91 | issue = 5 | pages = 1729–34 | date = May 2006 | pmid = 16507633 | doi = 10.1210/jc.2005-2400 | url = http://jcem.endojournals.org/cgi/pmidlookup?view=long&pmid=16507633 }}</ref><ref name=Dietlein_2007>{{cite journal | vauthors = Dietlein M, Wegscheider K, Vaupel R, Schmidt M, Schicha H | title = Management of multinodular goiter in Germany (Papillon 2005): do the approaches of thyroid specialists and primary care practitioners differ? | journal = Nuklearmedizin. Nuclear Medicine | volume = 46 | issue = 3 | pages = 65–75 | year = 2007 | pmid = 17549317 | doi = 10.1160/nukmed-0068 }}</ref> Levothyroxine is also used as interventional therapy in people with nodular thyroid disease or thyroid cancer to suppress thyroid-stimulating hormone (TSH) secretion.<ref name=Mandel>{{cite journal | vauthors = Mandel SJ, Brent GA, Larsen PR | title = Levothyroxine therapy in patients with thyroid disease | journal = Annals of Internal Medicine | volume = 119 | issue = 6 | pages = 492–502 | date = September 1993 | pmid = 8357116 | doi = 10.7326/0003-4819-119-6-199309150-00009 }}</ref> A subset of people with hypothyroidism treated with an appropriate dose of levothyroxine will describe continuing symptoms despite TSH levels in the normal range.<ref name="Gaitonde" /> In these people, further laboratory and clinical evaluation is warranted as they may have another cause for their symptoms.<ref name="Gaitonde" /> Furthermore, it is important to review their medications and possible dietary supplements as several medications can affect thyroid hormone levels.<ref name="Gaitonde" />
[[File:007815180lg Generic Levothyroxine.jpg|thumb|
Una mala adherència terapèutica en prendre la medicació és la causa més comuna de nivells elevats de TSH en persones que han rebut dosificacions apropiades de levotiroxina.<ref name="Gaitonde" />
▲[[File:007815180lg Generic Levothyroxine.jpg|thumb|Generic levothyroxine, 25 μg oral tablet]]
=== Pacients d'edat avançada ===
▲Dosages vary according to the age groups and the individual condition of the person, body weight and compliance to the medication and diet. Other predictors of the required dosage are [[sex]], [[Body mass index|BMI]], [[Sum activity of peripheral deiodinases|deiodinase activity (SPINA-GD)]] and [[etiology]] of [[hypothyroidism]].<ref name=pmid26335522>{{cite journal | vauthors = Midgley JE, Larisch R, Dietrich JW, Hoermann R | title = Variation in the biochemical response to <small>L</small>-thyroxine therapy and relationship with peripheral thyroid hormone conversion efficiency | journal = Endocrine Connections | volume = 4 | issue = 4 | pages = 196–205 | date = December 2015 | pmid = 26335522 | doi = 10.1530/EC-15-0056 | pmc=4557078}}</ref> Annual or semiannual clinical evaluations and TSH monitoring are appropriate after dosing has been established.<ref>{{EMedicine|article|122393|Hypothyroidism|treatment}}</ref> Levothyroxine is taken on an empty stomach approximately half an hour to an hour before meals.<ref name="RxList" /> As such, thyroid replacement therapy is usually taken 30 minutes prior to eating in the morning.<ref name="Gaitonde" /> For patients with trouble taking levothyroxine in the morning, bedtime dosing is effective as well.<ref name="Gaitonde" /> A recent study published in JAMA showed greater efficacy of levothyroxine when taken at bedtime.<ref>{{Cite news | title = Effects of Evening vs Morning Levothyroxine Intake: A Randomized Double-blind Crossover Trial | url = http://archinte.jamanetwork.com/article.aspx?articleid=776486 | url-status = live | archive-url = https://web.archive.org/web/20150906163348/http://archinte.jamanetwork.com/article.aspx?articleid=776486 | archive-date = 6 September 2015 | df = dmy-all }}</ref>
=== Embaràs i lactància ===
▲For older people (over 50 years old) and people with known or suspected [[Coronary artery disease|ischemic heart disease]], levothyroxine therapy should not be initiated at the full replacement dose.<ref name=Novothyrox>{{Cite web | title = Novothyrox (levothyroxine sodium tablets, USP) | url = http://www.accessdata.fda.gov/drugsatfda_docs/label/2009/021292s002lbl.pdf | access-date = 20 April 2014 | url-status = live | archive-url = https://web.archive.org/web/20130307010006/http://www.accessdata.fda.gov/drugsatfda_docs/label/2009/021292s002lbl.pdf | archive-date = 7 March 2013 | df = dmy-all }}</ref> Since thyroid hormone increases the heart's oxygen demand by increasing heart rate and contractility, starting at higher doses may cause an [[acute coronary syndrome]] or an [[arrhythmia|abnormal heart rhythm]].<ref name="Gaitonde" />
▲According to the U.S. [[Food and Drug Administration]] pregnancy categories, levothyroxine has been assigned Pregnancy Category A.<ref name="Novothyrox" /> Given that no increased risk of congenital abnormalities have been demonstrated in pregnant women taking levothyroxine, therapy should be continued during pregnancy.<ref name="Novothyrox" /> Furthermore, therapy should be immediately administered to women diagnosed with hypothyroidism during pregnancy, as hypothyroidism is associated with a higher rate of complications, such as spontaneous abortion, [[preeclampsia]], and premature birth.<ref name="Novothyrox" />
Thyroid hormone requirements increase during and last throughout pregnancy.<ref name="Gaitonde" /> As such, it is recommended that pregnant women increase to nine doses of levothyroxine each week, rather than the usual seven, as soon as their pregnancy is confirmed.<ref name="Gaitonde" /> Repeat thyroid function tests should be done five weeks after the dosage is increased.<ref name="Gaitonde" />
Linha 68 ⟶ 62:
Thyroxine was first isolated in pure form in 1914 at the [[Mayo Clinic]] by [[Edward Calvin Kendall]] from extracts of hog thyroid glands.<ref>{{Cite journal | title = The isolation in crystalline form of the compound containing iodin, which occurs in the thyroid: Its chemical nature and physiologic activity | vauthors = Kendall EC | journal = J. Am. Med. Assoc. | year = 1915 | volume = 64 | issue = 25 | pages = 2042–2043 | doi = 10.1001/jama.1915.02570510018005| url = https://zenodo.org/record/1423411 }}</ref> The hormone was [[Organic synthesis|synthesized]] in 1927 by British chemists [[Charles Robert Harington]] and [[George Barger]].
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== References ==
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