Pharmacokinetics

Ion Trapping

TRİyon Tuzaklanması
Also known as:pH trapping · pH partitioning

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.

Formula

Weak acid: Ctotal,1 / Ctotal,2 = (1 + 10^(pH1 − pKa)) / (1 + 10^(pH2 − pKa)) Weak base: Ctotal,1 / Ctotal,2 = (1 + 10^(pKa − pH1)) / (1 + 10^(pKa − pH2))

In depth

At equilibrium the concentration of the un-ionised form is the same on both sides of the membrane, but the total concentration is higher on the side where ionisation is greater, as predicted by the Henderson–Hasselbalch equation from the drug's pKa and the pH of each compartment (pH1, pH2). Weak acids therefore accumulate in more alkaline compartments and weak bases in more acidic ones.

Examples include the accumulation of weak bases in gastric juice, in breast milk (slightly more acidic than plasma) and in acidic intracellular organelles, and the enhanced renal excretion of weak acids such as salicylate and phenobarbital when the urine is alkalinised.

Clinical pearl

Urinary alkalinisation with sodium bicarbonate enhances salicylate elimination by trapping ionised salicylate in tubular urine and is a standard part of the management of significant salicylate poisoning.

Example drugs

Acetylsalicylic acid Phenobarbital
TRIn Turkish

İyon Tuzaklanması

Lipit membranlardan yalnızca iyonize olmamış form serbestçe geçebildiği için zayıf bir asit veya zayıf bir bazın, daha fazla iyonize olduğu membran tarafında birikmesidir.

Dengede iyonize olmamış formun konsantrasyonu membranın iki tarafında eşittir; ancak Henderson–Hasselbalch denkleminin ilacın pKa değeri ve her kompartmanın pH'sından (pH1, pH2) yola çıkarak öngördüğü gibi, toplam konsantrasyon iyonizasyonun daha fazla olduğu tarafta daha yüksektir. Bu nedenle zayıf asitler daha alkali, zayıf bazlar ise daha asidik kompartmanlarda birikir.

Zayıf bazların mide sıvısında, anne sütünde (plazmadan biraz daha asidik) ve asidik hücre içi organellerde birikmesi ile idrar alkalileştirildiğinde salisilat ve fenobarbital gibi zayıf asitlerin böbrekten atılımının artması buna örnektir.

Sodyum bikarbonatla idrarın alkalileştirilmesi, iyonize salisilatı tübül sıvısında tutarak salisilat eliminasyonunu artırır ve ciddi salisilat zehirlenmesinin standart tedavisinin bir parçasıdır.

Diğer adları:İyon tuzağı · pH tuzaklanması
Updated 24.09.2026 0 views Educational reference — verify against current sources before clinical use.

Read next

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.

 ExcretionAtılım (Ekskresyon)

The removal of unchanged drug or its metabolites from the body, principally in urine and in bile (faeces), and to a lesser extent in exhaled air, sweat, saliva and breast milk.

 Enhanced EliminationEliminasyonun Hızlandırılması

Measures that increase the removal of an already absorbed drug or toxin from the body beyond its intrinsic clearance, used in selected poisonings to shorten exposure and reduce toxicity.

 Blood–Brain BarrierKan–Beyin Bariyeri

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.

 AbsorptionAbsorpsiyon

The process by which a drug enters the bloodstream from the site of administration, such as the gastrointestinal tract, skin, or lungs.