Pharmacodynamics

Efficacy Emax

TREtkinlik
Also known as:Maximal efficacy · Maximal effect

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.

Formula

E = Emax × C / (EC50 + C)

In depth

In the Emax model, effect (E) rises with concentration (C) towards a plateau; efficacy corresponds to that plateau (Emax), whereas potency reflects the position of the curve on the concentration axis (EC50). At receptor level, efficacy describes how effectively an occupied receptor is activated and coupled to signalling: high in full agonists, lower in partial agonists and absent in antagonists.

Clinically, efficacy usually matters more than potency: loop diuretics have greater maximal natriuretic efficacy than thiazides, and full μ-opioid agonists greater maximal analgesic efficacy than partial agonists. In clinical trials, efficacy denotes benefit under ideal, controlled conditions, as distinct from effectiveness in routine practice.

Clinical pearl

Once a drug has reached its ceiling effect, further dose increases add adverse effects but no benefit; switching to a drug of higher efficacy or adding one with a different mechanism is then more rational.

Example drugs

Furosemide Hydrochlorothiazide Morphine Buprenorphine
TRIn Turkish

Etkinlik

Bir ilacın reseptörüne bağlandıktan sonra yanıt oluşturma kapasitesidir; klinik bağlamda doz ne kadar artırılırsa artırılsın ilacın oluşturabileceği en yüksek etkiyi (Emax) ifade eder.

Emax modelinde etki (E) konsantrasyonla (C) birlikte bir platoya doğru yükselir; etkinlik bu platoya (Emax), potens ise eğrinin konsantrasyon eksenindeki konumuna (EC50) karşılık gelir. Reseptör düzeyinde etkinlik, işgal edilmiş bir reseptörün aktive olma ve sinyal yolaklarına kenetlenme verimini tanımlar: tam agonistlerde yüksek, kısmi agonistlerde daha düşüktür, antagonistlerde ise yoktur.

Klinikte etkinlik genellikle potensten daha önemlidir: kıvrım diüretiklerinin maksimal natriüretik etkinliği tiyazidlerden, tam μ-opioid agonistlerin maksimal analjezik etkinliği kısmi agonistlerden yüksektir. Klinik araştırmalarda etkinlik (efficacy), rutin uygulamadaki etkililikten (effectiveness) farklı olarak ideal ve kontrollü koşullardaki yararı ifade eder.

İlaç tavan etkisine ulaştıktan sonra dozu artırmak yarar sağlamadan yalnızca advers etkileri artırır; bu durumda daha yüksek etkinlikli bir ilaca geçmek ya da farklı mekanizmalı bir ilaç eklemek daha akılcıdır.

Diğer adları:Efikasi · Maksimal etkinlik · Maksimal etki
Updated 24.09.2026 1 views Educational reference — verify against current sources before clinical use.

Read next

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.

 Intrinsic Activityİntrinsik 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.

 Dose–Response CurveDoz–Yanıt Eğrisi

A graph relating the dose or concentration of a drug to the magnitude of its effect (graded curve) or to the proportion of a population showing a specified all-or-none response (quantal curve).

 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.

 Half-Maximal Effective ConcentrationYarı Maksimal Etkili Konsantrasyon

The concentration of a drug that produces 50% of its own maximal effect (Emax); the standard measure of agonist potency in concentration–response studies.

 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.