Pharmacodynamics

Intrinsic Activity

TRİntrinsik Aktivite

The ability of a drug, once bound, to activate its receptor and produce a response, expressed relative to a full agonist on a scale from 0 (antagonist) to 1 (full agonist); inverse agonists have negative values.

Formula

α = Emax(drug) / Emax(full agonist)

In depth

The concept was introduced by Ariëns as the ratio (α) of a drug's maximal effect to that of a full agonist in the same tissue. Full agonists have α = 1, partial agonists 0 < α < 1, neutral antagonists α = 0 and inverse agonists a negative value.

Intrinsic activity is an observed, system-dependent property that varies with receptor density, coupling efficiency and the reference agonist chosen. The underlying receptor-level property is efficacy (Stephenson's concept, quantified in the operational model by the transducer ratio τ), so the terms are related but not strictly interchangeable. Clinically the term appears in the intrinsic sympathomimetic activity (ISA) of certain β-blockers.

Clinical pearl

β-blockers with intrinsic sympathomimetic activity (partial agonists such as pindolol and acebutolol) cause less resting bradycardia but are considered less suitable for secondary prevention after myocardial infarction.

Example drugs

Pindolol Acebutolol Buprenorphine
TRIn Turkish

İntrinsik Aktivite

Bir ilacın bağlandıktan sonra reseptörünü aktive ederek yanıt oluşturma yeteneğidir; tam agoniste göre 0 (antagonist) ile 1 (tam agonist) arasındaki bir ölçekte ifade edilir, ters agonistlerde ise negatif değer alır.

Kavram Ariëns tarafından, bir ilacın maksimal etkisinin aynı dokuda tam agonistin maksimal etkisine oranı (α) olarak tanımlanmıştır. Tam agonistlerde α = 1, kısmi agonistlerde 0 < α < 1, nötr antagonistlerde α = 0'dır; ters agonistlerde ise α negatif bir değer alır.

İntrinsik aktivite gözleme dayalı ve sisteme bağımlı bir özelliktir; reseptör yoğunluğuna, kenetlenme verimine ve referans alınan agoniste göre değişir. Bunun altında yatan reseptör düzeyindeki özellik etkinliktir (Stephenson kavramı; operasyonel modelde transdüksiyon oranı τ ile nicelendirilir); bu nedenle iki terim ilişkili olmakla birlikte tam eş anlamlı değildir. Klinikte terim, bazı β-blokerlerin intrinsik sempatomimetik aktivitesi (İSA) ifadesinde geçer.

İntrinsik sempatomimetik aktiviteye sahip β-blokerler (pindolol ve asebutolol gibi kısmi agonistler) istirahatte daha az bradikardi yapar, ancak miyokard infarktüsü sonrası sekonder korunmada daha az uygun kabul edilir.

Diğer adları:İntrensek aktivite · İç aktivite
Updated 24.09.2026 0 views Educational reference — verify against current sources before clinical use.

Read next

EfficacyEtkinlik

The capacity of a drug to produce a response once bound to its receptor; in clinical terms, the maximal effect (Emax) a drug can produce, however much the dose is increased.

 Partial AgonistKısmi Agonist

An agonist that, even when occupying all available receptors, produces a maximal response smaller than that of a full agonist; its intrinsic activity lies between 0 and 1.

 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.

 AffinityAfinite

The strength of binding between a drug and its receptor or target, determined by the rates of association and dissociation and usually expressed as the equilibrium dissociation constant (Kd) or its negative logarithm (pKd).

 Spare ReceptorsYedek Reseptörler

Receptors in excess of those needed to produce a maximal response, so that a full agonist can elicit its maximal effect while occupying only a fraction of the available receptors.