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Nanahuatl (mesaj | katkılar)
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k Nanahuatl, H₂-reseptör antagonisti sayfasını H2 antagonisti sayfasına taşıdı: düzeltme
Nanahuatl (mesaj | katkılar)
Devriyeler
539.182 değişiklik
k düzeltme
1. satır:
{{DISPLAYTITLE:H<sub>2</sub>-reseptör antagonisti}}
[[Dosya:Cimetidine.svg|thumb|[[Simetidin]], H<sub>2</sub>-reseptör antagonistlerinin prototipi.]]
'''H<sub>2</sub>-reseptör antagonistleri''', [[mide]] paryetal hücresinde [[histamin]]in etkisini bloke ederek bu hücrelerdeki asit salınımını azaltan moleküllerdir. Bu ilaçlar [[dispepsi]] tedavisinde kullanılır. Ancak [[proton pompa inhibitörleri]]ne göre daha az etkili kaldıklarından kullanımları sınırlıdır.
15. satır:
Metiamid etkili bir ajandı ancak [[nefrotoksik]] idi ve [[agranülositoz]] yapıyordu.
 
<!--It was proposed that the toxicity arose from the [[thiourea]] group, and similar [[guanidine]]-analogues were investigated until the ultimate discovery of [[Cimetidine]] (common brand name Tagamet).
 
[[Ranitidine]] (common brand name Zantac) was developed by Glaxo (also now [[GlaxoSmithKline]]) in an effort to match the success of Smith, Kline & French with cimetidine. Ranitidine was also the result of a rational drug design process utilising the by-then-fairly-refined model of the histamine H<sub>2</sub> receptor and quantitative structure-activity relationships ([[QSAR]]).
 
Glaxo refined the model further by replacing the [[imidazole]]-ring of cimetidine with a [[furan]]-ring with a [[nitrogen]]-containing substituent, and in doing so developed ranitidine. Ranitidine was found to have a far-improved tolerability profile (i.e. fewer [[adverse drug reaction]]s), longer-lasting action, and ten times the activity of cimetidine.
 
Ranitidine was introduced in [[1981]] and was the world's biggest-selling prescription drug by [[1988]]. The H<sub>2</sub>-receptor antagonists have since largely been superseded by the even more effective [[proton pump inhibitor]]s, with [[omeprazole]] becoming the biggest-selling drug for many years.
 
== Pharmacology ==
The H<sub>2</sub> antagonists are competitive inhibitors of [[histamine]] at the [[parietal cell]] H<sub>2</sub> receptor. They suppress the normal secretion of acid by parietal cells and the meal-stimulated secretion of acid. They accomplish this by two mechanisms: histamine released by [[ECL cell]]s in the stomach is blocked from binding on parietal cell H<sub>2</sub> receptors which stimulate acid secretion, and other substances that promote acid secretion (such as [[gastrin]] and [[acetylcholine]]) have a reduced effect on parietal cells when the H<sub>2</sub> receptors are blocked.
 
==Clinical use of H<sub>2</sub>-antagonists==
=== Indications ===
H<sub>2</sub>-antagonists are clinically used in the treatment of acid-related [[gastrointestinal]] conditions. Specifically, these indications may include:<ref name="Rossi">Rossi S (Ed.) (2005). [[Australian Medicines Handbook]] 2005. Adelaide: Australian Medicines Handbook. ISBN 0-9578521-9-3</ref>
*[[peptic ulcer]] disease (PUD)
*[[gastroesophageal reflux disease]] (GERD)
*[[dyspepsia]]
*stress ulcer prophylaxis (raniditine)
 
People that suffer from heartburn (GERD) infrequently may take either [[antacids]] or H<sub>2</sub>-receptor antagonists for treatment. H<sub>2</sub>-antagonists offer several advantages over antacids including longer duration of action (6–10 hours vs 1–2 hours for antacids), greater efficacy, and ability to be used prophylactically before meals to reduce the chance of heartburn occurring. [[Proton pump inhibitors]], however, are the preferred treatment for [[erosive oesophagitis]] since they have been shown to promote healing better than H<sub>2</sub>-antagonists.
 
Some studies also suggest that H<sub>2</sub>-antagonists might be effective in treating [[herpes virus]]es, such as [[shingles]] and [[herpes simplex]] [http://www.lef.org/magazine/mag2001/mar2001_report_tagamet_1.html].
 
=== Adverse drug reactions ===
H<sub>2</sub> antagonists are generally well-tolerated, except for [[cimetidine]] where all of the following [[adverse drug reaction]]s (ADRs) are ''common''. Infrequent ADRs include [[hypotension]]. Rare ADRs include: [[headache]], tiredness, dizziness, confusion, [[diarrhoea]], constipation, and rash.<ref name="Rossi"> </ref> Additionally, cimetidine may also cause [[gynecomastia]] in males, loss of libido, and [[impotence]], which are reversible upon discontinuation.
 
=== Drug interactions ===
With regard to [[pharmacokinetics]], cimetidine in particular interferes with some of the body's mechanisms of [[drug metabolism]] and elimination through the liver [[cytochrome P450]] pathway. Specifically, cimetidine is an inhibitor of the P450 enzymes [[CYP1A2]], [[CYP2C9]], [[CYP2C19]], [[CYP2D6]], [[CYP2E1]], and [[CYP3A4]]. By reducing the metabolism of drugs through these enzymes, cimetidine may increase their [[blood plasma|serum]] [[concentration]]s to [[toxic]] levels. Examples of drugs affected include: [[warfarin]], [[theophylline]], [[phenytoin]], [[lidocaine]], [[quinidine]], [[propranolol]], [[labetalol]], [[metoprolol]], [[tricyclic antidepressants]], some [[benzodiazepines]], dihydropyridine [[calcium channel blocker]]s, [[sulfonylureas]], [[metronidazole]], and some recreational drugs such as [[ethanol]] and [[MDMA]].
 
== Examples ==
Cimetidine was the prototypical member of the H<sub>2</sub> antagonists. Further developments, using quantitative structure-activity relationships ([[QSAR]]) led to the development of further agents with improved tolerability-profiles. In the United States, all four members of the group are available over the counter in relatively low doses, and have become extremely popular medications marketed to heartburn sufferers.
 
*[[cimetidine]] (Tagamet)
*[[ranitidine]] (Zantac)
*[[famotidin]] (Famodin)
*[[nizatidine]] (Axid, Tazac)
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== Kaynakça ==
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