Pharmacokinetics

Blood–Brain Barrier BBB

TRKan–Beyin Bariyeri
Also known as:Blood-brain barrier · Haematoencephalic barrier

A selective barrier formed by brain capillary endothelial cells joined by tight junctions and supported by pericytes and astrocyte end-feet, which restricts the passage of drugs and solutes from blood into the central nervous system.

In depth

Because paracellular passage is blocked and transcytosis is minimal, drugs enter the brain mainly by passive diffusion through endothelial cells: small, lipophilic, un-ionised molecules cross readily, whereas polar and large molecules do not. Efflux transporters, notably P-glycoprotein and BCRP, pump many substrates back into the blood, while carrier systems take up nutrients such as glucose and large neutral amino acids.

The barrier is exploited therapeutically: levodopa enters the brain via the large neutral amino acid transporter, whereas loperamide, domperidone and second-generation antihistamines have limited central effects because of low CNS penetration.

Clinical pearl

Meningeal inflammation increases entry of polar antibiotics such as β-lactams into the cerebrospinal fluid, and penetration may fall as inflammation resolves; the chemoreceptor trigger zone lies outside the barrier, so domperidone remains antiemetic.

Example drugs

Levodopa Loperamide Domperidone Fexofenadine
TRIn Turkish

Kan–Beyin Bariyeri

Sıkı bağlantılarla birbirine bağlanan beyin kapiller endotel hücrelerinin oluşturduğu, perisitler ve astrosit ayaksı uzantılarıyla desteklenen, ilaçların ve çözünmüş maddelerin kandan merkezi sinir sistemine geçişini sınırlayan seçici engeldir.

Hücreler arası geçiş engellendiğinden ve transsitoz çok sınırlı olduğundan ilaçlar beyne esas olarak endotel hücrelerinden pasif difüzyonla girer: küçük, lipofilik ve iyonize olmamış moleküller kolayca geçerken polar ve büyük moleküller geçemez. Başta P-glikoprotein ve BCRP olmak üzere efluks taşıyıcıları pek çok substratı kana geri pompalar; taşıyıcı sistemler ise glukoz ve büyük nötral amino asitler gibi besin maddelerinin alımını sağlar.

Bu engelden tedavide yararlanılır: levodopa beyne büyük nötral amino asit taşıyıcısıyla girer; loperamid, domperidon ve ikinci kuşak antihistaminikler ise merkezi sinir sistemine az geçtikleri için sınırlı santral etki gösterir.

Meninks inflamasyonu β-laktamlar gibi polar antibiyotiklerin beyin omurilik sıvısına geçişini artırır ve inflamasyon geriledikçe geçiş azalabilir; kemoreseptör tetik bölgesi bu engelin dışında kaldığından domperidon antiemetik etkisini korur.

Diğer adları:Kan-beyin engeli · Hematoensefalik bariyer
Updated 24.09.2026 0 views Educational reference — verify against current sources before clinical use.

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DistributionDağılım

The reversible transfer of a drug from the bloodstream into the interstitial and intracellular fluids and tissues of the body after it has reached the systemic circulation.

 P-glycoproteinP-glikoprotein

An ATP-dependent efflux transporter (ABCB1, MDR1) that pumps a wide range of drugs out of cells, limiting their intestinal absorption and brain entry and promoting their biliary and renal excretion.

 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.

 Ion Trappingİyon Tuzaklanması

The accumulation of a weak acid or weak base on the side of a membrane where it is more ionised, because only the un-ionised form diffuses freely across lipid membranes.

 Volume of DistributionSanal Dağılım Hacmi

A theoretical volume that describes the extent to which a drug is distributed throughout the body tissues relative to the plasma, indicating how much the drug leaves the bloodstream to enter tissues.

 Henderson–Hasselbalch EquationHenderson–Hasselbalch Denklemi

An equation relating the pH of a solution and the pKa of a weak acid or base to the ratio of its ionised and un-ionised forms, used to predict drug ionisation, absorption and distribution.