Pharmacodynamics

Antagonist

Also known as:Receptor antagonist · Blocker

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.

In depth

Receptor antagonists are classified as competitive (reversible, surmountable) or non-competitive, including irreversible (insurmountable), according to whether increasing the agonist concentration can overcome the block; allosteric antagonists act at a separate site. Antagonism can also occur without receptor blockade: physiological antagonism (opposing effects through different receptors), chemical antagonism (direct binding and inactivation) and pharmacokinetic antagonism (reduced agonist concentration at its site of action).

A neutral antagonist has no effect of its own; its effect is proportional to the prevailing agonist tone.

Clinical pearl

Antagonist effects depend on existing agonist tone: propranolol slows heart rate more during exercise than at rest, and naloxone has little effect in an opioid-naive person but precipitates withdrawal in a dependent one.

Example drugs

Naloxone Propranolol Atropine Losartan
TRIn Turkish

Antagonist

Bir reseptöre veya başka bir hedefe bağlanıp onu aktive etmeyen (afinitesi olan ancak etkinliği olmayan) ve böylece bir agonistin oluşturduğu yanıtı önleyen veya azaltan ilaçtır.

Reseptör antagonistleri, agonist konsantrasyonunun artırılmasıyla bloğun aşılıp aşılamamasına göre yarışmalı (geri dönüşümlü, aşılabilir) ya da geri dönüşümsüz olanlar da dahil yarışmasız (aşılamaz) olarak sınıflandırılır; allosterik antagonistler ayrı bir bölge üzerinden etki eder. Antagonizma reseptör blokajı olmaksızın da ortaya çıkabilir: fizyolojik antagonizma (farklı reseptörler aracılığıyla zıt etkiler), kimyasal antagonizma (doğrudan bağlanma ve inaktivasyon) ve farmakokinetik antagonizma (agonistin etki yerindeki konsantrasyonunun azalması).

Nötr antagonistin kendine ait bir etkisi yoktur; oluşturduğu etki ortamdaki agonist tonusuyla orantılıdır.

Antagonist etkisi mevcut agonist tonusuna bağlıdır: propranolol kalp hızını istirahate göre egzersiz sırasında daha fazla yavaşlatır; nalokson opioid kullanmayan bir kişide belirgin etki oluşturmazken bağımlı bir kişide yoksunluğu tetikler.

Diğer adları:Reseptör antagonisti · Bloker
Updated 24.09.2026 0 views Educational reference — verify against current sources before clinical use.

Read next

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.

 Non-Competitive AntagonismYarışmasız Antagonizma

Antagonism that cannot be overcome by increasing the agonist concentration, because the antagonist binds irreversibly or acts at a site or step distinct from agonist binding; the maximal agonist response is reduced.

 Physiological AntagonismFizyolojik Antagonizma

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

 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.

 AgonistAgonist

A drug or endogenous substance that binds to a receptor and activates it, producing a biological response; it possesses both affinity and efficacy (intrinsic activity).

 Inverse AgonistTers Agonist

A ligand that binds to a receptor with constitutive (ligand-independent) activity and reduces that basal activity, producing an effect opposite in direction to that of an agonist.