Pharmacodynamics

Selectivity

TRSeçicilik
Also known as:Drug selectivity · Receptor selectivity

The degree to which a drug acts on a particular target (receptor subtype, enzyme or tissue) rather than on others, usually expressed as the ratio of its affinities or potencies at different targets.

Formula

Selectivity ratio = Ki (off-target) / Ki (intended target)

In depth

Selectivity is relative and concentration-dependent: a selective drug acts preferentially on one target at therapeutic concentrations but loses selectivity as concentrations rise. It is quantified as a selectivity ratio, for example the ratio of Ki or IC50 values at an off-target and at the intended target. Specificity, action on a single target only, is rarely achieved.

Selectivity largely shapes the adverse-effect profile: β1-selective (cardioselective) blockers cause less bronchoconstriction than non-selective ones, and COX-2-selective inhibitors cause less gastrointestinal injury than non-selective NSAIDs without removing cardiovascular risk. Tissue selectivity can also be achieved by local delivery, as with inhaled drugs.

Clinical pearl

β1-selectivity is dose-dependent and incomplete, so even cardioselective β-blockers can cause bronchospasm; in asthma β-blockers are usually avoided, and a cardioselective agent is used only with caution when there is no alternative.

Example drugs

Bisoprolol Metoprolol Celecoxib Tamsulosin
TRIn Turkish

Seçicilik

Bir ilacın diğer hedeflere kıyasla belirli bir hedef (reseptör alt tipi, enzim veya doku) üzerinde etki gösterme derecesidir; genellikle farklı hedeflerdeki afinite ya da potens değerlerinin oranıyla ifade edilir.

Seçicilik göreceli ve konsantrasyona bağımlıdır: seçici bir ilaç terapötik konsantrasyonlarda tercihen tek bir hedefe etki eder, ancak konsantrasyon arttıkça seçiciliğini yitirir. Seçicilik, örneğin istenmeyen hedefteki Ki veya IC50 değerinin asıl hedefteki değere oranı gibi bir seçicilik oranıyla nicelendirilir. Yalnızca tek bir hedefe etki anlamına gelen özgüllüğe (spesifisite) ise nadiren ulaşılır.

Seçicilik advers etki profilini büyük ölçüde belirler: β1-seçici (kardiyoselektif) blokerler seçici olmayanlara göre daha az bronkokonstriksiyon yapar; COX-2 seçici inhibitörler seçici olmayan NSAİİ'lere göre daha az gastrointestinal hasara yol açar, ancak kardiyovasküler riski ortadan kaldırmaz. Doku seçiciliği, inhale ilaçlarda olduğu gibi lokal uygulamayla da sağlanabilir.

β1 seçiciliği doza bağımlıdır ve tam değildir; bu nedenle kardiyoselektif β-blokerler bile bronkospazma yol açabilir. Astımda β-blokerlerden genellikle kaçınılır; alternatif yoksa kardiyoselektif bir ajan ancak dikkatle kullanılır.

Diğer adları:Selektivite · Seçici etki
Updated 24.09.2026 0 views Educational reference — verify against current sources before clinical use.

Read next

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).

 PotencyPotens

The amount or concentration of a drug needed to produce an effect of a given intensity, usually expressed as the EC50 or ED50; the lower the value, the more potent the drug.

 ReceptorReseptör

A macromolecule, usually a protein, to which a drug or endogenous ligand binds specifically and thereby initiates a change in cell function that produces a biological response.

 Inhibition Constantİnhibisyon Sabiti

The equilibrium dissociation constant of an inhibitor from its enzyme, receptor or transporter; an assay-independent measure of inhibitor affinity, with lower Ki values indicating more potent inhibition.

 Side EffectYan Etki

An unintended effect of a medicine, occurring at normal doses, that arises from its pharmacological properties and may be harmful, neutral or occasionally beneficial.

 Therapeutic IndexTerapötik İndeks

A measure of a drug's relative safety, classically the ratio of the dose producing toxicity (TD50) or death (LD50) in 50% of subjects to the dose producing the desired effect in 50% (ED50).