Pharmacodynamics

Partial Agonist

TRKısmi 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.

In depth

Because a partial agonist occupies receptors but activates them less effectively, it acts as an agonist when endogenous tone is low but as a functional antagonist in the presence of a full agonist, with which it competes for the same receptors. The observed maximal effect depends on receptor reserve and tissue sensitivity, so a drug may behave as a full agonist in one tissue and as a partial agonist in another.

Clinically important partial agonists include buprenorphine (μ-opioid receptor), varenicline (α4β2 nicotinic receptor), aripiprazole (dopamine D2 receptor) and pindolol, a β-blocker with intrinsic sympathomimetic activity.

Clinical pearl

Starting buprenorphine while a high level of a full opioid agonist is still present can precipitate withdrawal, so induction usually waits until objective signs of mild-to-moderate withdrawal appear.

Example drugs

Buprenorphine Varenicline Aripiprazole Pindolol
TRIn Turkish

Kısmi Agonist

Mevcut reseptörlerin tamamını işgal ettiğinde bile tam agonistten daha düşük bir maksimal yanıt oluşturan agonisttir; intrinsik aktivitesi 0 ile 1 arasındadır.

Kısmi agonist reseptörleri işgal eder ancak onları daha az etkili biçimde aktive eder; bu nedenle endojen tonus düşükken agonist gibi, tam agonist varlığında ise aynı reseptörler için onunla yarışarak işlevsel antagonist gibi davranır. Gözlenen maksimal etki reseptör rezervine ve doku duyarlılığına bağlıdır; dolayısıyla aynı ilaç bir dokuda tam agonist, başka bir dokuda kısmi agonist gibi davranabilir.

Klinik açıdan önemli kısmi agonistler arasında buprenorfin (μ-opioid reseptörü), vareniklin (α4β2 nikotinik reseptörü), aripiprazol (dopamin D2 reseptörü) ve intrinsik sempatomimetik aktiviteye sahip bir β-bloker olan pindolol sayılabilir.

Vücutta hâlâ yüksek düzeyde tam opioid agonisti varken buprenorfine başlanması tetiklenmiş (presipite) yoksunluğa yol açabilir; bu nedenle indüksiyon genellikle hafif-orta şiddette yoksunluğun objektif bulguları ortaya çıkana kadar ertelenir.

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

Read next

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).

 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.

 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.

 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.

 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.

 Withdrawal SyndromeYoksunluk Sendromu

A characteristic cluster of signs and symptoms that follows abrupt discontinuation, rapid dose reduction or antagonist reversal of a drug to which the body has adapted during prolonged use.