Drug Interactions

Physiological Antagonism

TRFizyolojik Antagonizma
Also known as:Functional antagonism

Opposition between two drugs that act on different receptors or pathways to produce opposing physiological effects, so that each counteracts the other's action.

In depth

Unlike receptor (pharmacological) antagonism, the antagonist does not act at the agonist's receptor, so the degree of opposition depends on the relative size of two independent effects rather than on receptor occupancy. The classic example is epinephrine reversing histamine-induced bronchoconstriction and hypotension in anaphylaxis through β2 and α1 receptors, whereas histamine acts through H1 receptors.

Other examples include glucagon raising blood glucose against insulin and glucocorticoids opposing the glucose-lowering effect of antidiabetic drugs. The term functional antagonism is often used when both agonists act on the same cell or tissue.

Clinical pearl

Epinephrine, not an antihistamine, is first-line in anaphylaxis because physiological antagonism counteracts the effects of all released mediators, whereas H1 blockers only prevent further histamine action.

Example drugs

Epinephrine Glucagon insulin
TRIn Turkish

Fizyolojik Antagonizma

Farklı reseptörler veya yolaklar üzerinden birbirine zıt fizyolojik etkiler oluşturan iki ilacın birbirinin etkisini karşıladığı antagonizma türüdür.

Reseptör (farmakolojik) antagonizmasından farklı olarak antagonist, agonistin reseptörüne etki etmez; bu nedenle karşıtlığın derecesi reseptör işgaline değil, iki bağımsız etkinin göreli büyüklüğüne bağlıdır. Klasik örnek, anafilakside histaminin H1 reseptörleri aracılığıyla oluşturduğu bronkokonstriksiyon ve hipotansiyonun adrenalin tarafından β2 ve α1 reseptörleri üzerinden tersine çevrilmesidir.

Diğer örnekler arasında glukagonun insüline karşı kan şekerini yükseltmesi ve glukokortikoidlerin antidiyabetik ilaçların kan şekerini düşürücü etkisine karşı koyması sayılabilir. İki agonist aynı hücre veya doku üzerinde etki ettiğinde sıklıkla fonksiyonel antagonizma terimi kullanılır.

Anafilakside birinci basamak ilaç antihistaminik değil adrenalindir; çünkü fizyolojik antagonizma salınan tüm mediyatörlerin etkilerine karşı koyarken H1 blokerleri yalnızca histaminin sonraki etkilerini önler.

Diğer adları:Fonksiyonel antagonizma
Updated 24.09.2026 1 views Educational reference — verify against current sources before clinical use.

Read next

Chemical AntagonismKimyasal Antagonizma

Inactivation of a drug by direct chemical combination with another substance to form an inactive complex, independently of receptors or physiological effects.

 Competitive AntagonismYarışmalı Antagonizma

Reversible antagonism in which the antagonist binds to the same site as the agonist, so the block can be overcome by raising the agonist concentration; the agonist curve shifts to the right in parallel without a fall in maximal response.

 AntagonistAntagonist

A drug that binds to a receptor or other target without activating it (affinity but no efficacy) and thereby prevents or reduces the response to an agonist.

 Pharmacodynamic InteractionFarmakodinamik Etkileşim

An interaction in which one drug modifies the response to another at the same or related receptors, physiological systems or pathways, independently of any change in plasma concentrations.

 AnaphylaxisAnafilaksi

A severe, potentially life-threatening systemic hypersensitivity reaction of rapid onset that causes airway, breathing or circulatory compromise, usually but not always with skin or mucosal changes.

 AntidoteAntidot

A substance that counteracts the effects of a poison or drug overdose by preventing its absorption, binding or inactivating it, antagonising it at its site of action, enhancing its elimination or reversing its toxic effects.