General Pharmacology

Xenobiotic

TRKsenobiyotik
Also known as:Foreign compound

A chemical that is foreign to an organism, being neither produced by it nor part of its normal biochemistry; drugs, environmental pollutants, food additives and many plant toxins are examples.

In depth

Organisms handle xenobiotics through a coordinated defence system: phase I reactions (mainly cytochrome P450 oxidation) introduce or expose functional groups, phase II reactions conjugate them with polar moieties such as glucuronic acid, sulfate or glutathione, and efflux transporters (sometimes termed phase III) export the products into bile or urine. Many of these pathways are induced on repeated exposure via the nuclear receptors PXR and CAR and the aryl hydrocarbon receptor (AhR).

The same enzymes also metabolise some endogenous compounds such as steroids and bilirubin. Metabolism usually detoxifies xenobiotics but can also generate reactive metabolites, as when paracetamol is converted to NAPQI.

Clinical pearl

Environmental xenobiotics matter clinically: polycyclic aromatic hydrocarbons in tobacco smoke induce CYP1A2 and lower clozapine and theophylline concentrations, so stopping smoking can precipitate toxicity.

Example drugs

paracetamol Clozapine Theophylline
TRIn Turkish

Ksenobiyotik

Organizma tarafından üretilmeyen ve normal biyokimyasında yer almayan, dolayısıyla organizmaya yabancı olan kimyasal maddedir; ilaçlar, çevresel kirleticiler, gıda katkı maddeleri ve birçok bitki toksini bu gruptadır.

Organizmalar ksenobiyotiklerle eşgüdümlü bir savunma sistemi aracılığıyla baş eder: faz I tepkimeleri (başlıca sitokrom P450 oksidasyonu) fonksiyonel gruplar ekler veya açığa çıkarır, faz II tepkimeleri bunları glukuronik asit, sülfat veya glutatyon gibi polar gruplarla konjuge eder, efluks taşıyıcıları (bazen faz III olarak adlandırılır) ise ürünleri safraya veya idrara aktarır. Bu yolların birçoğu tekrarlanan maruziyetle PXR ve CAR nükleer reseptörleri ile aril hidrokarbon reseptörü (AhR) aracılığıyla indüklenir.

Aynı enzimler steroidler ve bilirubin gibi bazı endojen bileşikleri de metabolize eder. Metabolizma ksenobiyotikleri genellikle detoksifiye eder, ancak parasetamolün NAPQI'ye dönüşmesinde olduğu gibi reaktif metabolitler de oluşturabilir.

Çevresel ksenobiyotiklerin klinik önemi vardır: sigara dumanındaki polisiklik aromatik hidrokarbonlar CYP1A2'yi indükleyerek klozapin ve teofilin konsantrasyonlarını düşürür; bu nedenle sigaranın bırakılması toksisiteye yol açabilir.

Diğer adları:Yabancı madde · Yabancı bileşik
Updated 24.09.2026 1 views Educational reference — verify against current sources before clinical use.

Read next

Drug Metabolismİlaç Metabolizması

The enzymatic biotransformation of drugs and other xenobiotics into metabolites that are usually more polar and more readily excreted, occurring mainly in the liver.

 Phase I MetabolismFaz I Metabolizma

Functionalization reactions, mainly oxidation, reduction and hydrolysis, that introduce or unmask a polar group such as –OH, –NH2 or –COOH on a drug molecule.

 Phase II MetabolismFaz II Metabolizma

Conjugation reactions in which an endogenous moiety such as glucuronic acid, sulfate, glutathione, an acetyl or a methyl group is attached to a drug or to its phase I metabolite.

 Cytochrome P450Sitokrom P450

A superfamily of heme-containing monooxygenase enzymes, located mainly in the endoplasmic reticulum of hepatocytes and enterocytes, that catalyze most phase I oxidative drug metabolism.

 Enzyme InductionEnzim İndüksiyonu

An increase in the amount and activity of a drug-metabolizing enzyme or transporter, usually through enhanced gene transcription, caused by repeated exposure to a drug or other xenobiotic.

 Drug Transporterİlaç Taşıyıcısı

A membrane protein that moves drugs across cell membranes, either into cells (uptake) or out of them (efflux), and thereby influences absorption, distribution and elimination.