Pharmacodynamics

Tachyphylaxis

TRTaşifilaksi
Also known as:Acute tolerance

A rapidly developing decrease in response to a drug after repeated doses over a short period (minutes to hours), which often cannot be overcome by increasing the dose.

In depth

Mechanisms include depletion of mediators, as when repeated doses of indirectly acting sympathomimetics (e.g. ephedrine, amphetamine, tyramine) exhaust releasable noradrenaline stores, and rapid receptor desensitisation through phosphorylation, β-arrestin binding and internalisation.

Tachyphylaxis is distinguished from tolerance chiefly by its speed: it develops acutely, over minutes to hours, and usually resolves soon after the drug is withheld, whereas tolerance develops gradually over days to weeks. The terms are sometimes used interchangeably, but pharmacology texts reserve tachyphylaxis for the rapid form.

Clinical pearl

Repeated boluses of ephedrine lose effect as noradrenaline stores are depleted; a direct-acting vasopressor such as phenylephrine is then more reliable.

Example drugs

Ephedrine Amphetamine
TRIn Turkish

Taşifilaksi

Bir ilacın kısa süre içinde (dakikalar ile saatler) tekrarlanan dozlarından sonra hızla gelişen ve doz artırılarak çoğu zaman aşılamayan yanıt azalmasıdır.

Mekanizmalar arasında aracı maddelerin tükenmesi (örneğin dolaylı etkili sempatomimetiklerin [efedrin, amfetamin, tiramin] tekrarlanan dozlarının salıverilebilir noradrenalin depolarını tüketmesi) ve fosforilasyon, β-arrestin bağlanması ve internalizasyon yoluyla gelişen hızlı reseptör desensitizasyonu yer alır.

Taşifilaksi toleranstan esas olarak gelişme hızıyla ayrılır: akut olarak, dakikalar ile saatler içinde gelişir ve ilaç kesildikten kısa süre sonra genellikle düzelir; tolerans ise günler ile haftalar içinde yavaş yavaş gelişir. İki terim zaman zaman birbirinin yerine kullanılsa da farmakoloji kaynakları taşifilaksi terimini hızlı gelişen form için kullanır.

Tekrarlanan efedrin bolusları, noradrenalin depoları tükendikçe etkisini yitirir; bu durumda fenilefrin gibi doğrudan etkili bir vazopresör daha güvenilir sonuç verir.

Diğer adları:Akut tolerans
Updated 24.09.2026 0 views Educational reference — verify against current sources before clinical use.

Read next

ToleranceTolerans

A gradual reduction in response to a drug with repeated or continuous exposure, so that a higher dose is needed to reproduce the original effect; it develops over days to weeks.

 Receptor Down-RegulationReseptör Down-Regülasyonu

A decrease in the number of receptors available at the cell surface or in the cell, typically in response to prolonged or excessive agonist stimulation, which reduces tissue responsiveness.

 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).

 Rebound EffectRebound Etkisi

The return of the condition being treated, at an intensity exceeding pre-treatment levels, after a drug is stopped or its dose is rapidly reduced.

 G Protein-Coupled ReceptorG Proteinine Kenetli Reseptör

A member of the largest family of cell-surface receptors, a single polypeptide with seven transmembrane α-helices that transduces ligand binding into intracellular signals by activating heterotrimeric G proteins.

 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.