Pharmaceutics & Dosage Forms

Solubility

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Also known as:Equilibrium solubility

The maximum amount of a substance that dissolves in a given volume of solvent at equilibrium under specified conditions of temperature, pH and medium composition.

Formula

S = S0 × (1 + 10^(pH − pKa)) (weak acid) S = S0 × (1 + 10^(pKa − pH)) (weak base)

In depth

Aqueous solubility depends on crystal lattice energy, lipophilicity, ionisation and solid-state form (polymorph, hydrate, amorphous form, salt). For weak acids and bases, total solubility (S) varies with pH according to the Henderson–Hasselbalch relationship, rising above the intrinsic solubility of the un-ionised form (S0) as ionisation increases; a weak base such as ketoconazole therefore dissolves better in acidic gastric fluid.

In the Biopharmaceutics Classification System a drug is highly soluble when its highest single therapeutic dose dissolves in 250 mL or less of aqueous media over pH 1.2–6.8 at 37 °C. Poor solubility limits oral bioavailability and is common among new chemical entities.

Clinical pearl

Drugs whose solubility depends on gastric acid (for example, ketoconazole, itraconazole capsules and several kinase inhibitors) can be poorly absorbed when taken with proton pump inhibitors or H2-receptor antagonists.

Example drugs

Ketoconazole Itraconazole
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Çözünürlük

Belirli sıcaklık, pH ve ortam bileşimi koşullarında, dengede, belirli hacimdeki bir çözücüde çözünebilen en fazla madde miktarıdır.

Sudaki çözünürlük kristal örgü enerjisine, lipofilisiteye, iyonlaşmaya ve katı hâl formuna (polimorf, hidrat, amorf form, tuz) bağlıdır. Zayıf asit ve bazlarda toplam çözünürlük (S) Henderson–Hasselbalch ilişkisine göre pH ile değişir ve iyonlaşma arttıkça iyonlaşmamış formun intrinsik çözünürlüğünün (S0) üzerine çıkar; bu nedenle ketokonazol gibi zayıf bir baz asidik mide sıvısında daha iyi çözünür.

Biyofarmasötik Sınıflandırma Sistemi'nde en yüksek tek terapötik doz 37 °C'de pH 1,2–6,8 aralığında 250 mL veya daha az sulu ortamda çözünüyorsa ilaç yüksek çözünürlüklü kabul edilir. Düşük çözünürlük oral biyoyararlanımı sınırlar ve yeni kimyasal moleküllerde sık görülür.

Çözünürlüğü mide asidine bağlı ilaçlar (örneğin ketokonazol, itrakonazol kapsül ve bazı kinaz inhibitörleri) proton pompası inhibitörleri veya H2 reseptör antagonistleriyle birlikte alındığında yetersiz absorbe edilebilir.

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

Read next

DissolutionÇözünme (Dissolüsyon)

The process by which a solid drug passes into solution in a solvent such as gastrointestinal fluid; for solid oral dosage forms it is a prerequisite for absorption and often its rate-limiting step.

 Biopharmaceutics Classification SystemBiyofarmasötik Sınıflandırma Sistemi

A scientific framework that classifies drug substances into four classes according to their aqueous solubility and intestinal permeability, the two main determinants of the rate and extent of oral absorption.

 Salt FormTuz Formu

A form of an ionisable drug substance combined with a pharmaceutically acceptable counterion, such as hydrochloride, sodium, maleate or mesilate, chosen to improve solubility, stability, crystallinity or manufacturability.

 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.

 BioavailabilityBiyoyararlanım

The fraction of an administered dose that reaches the systemic circulation unchanged, and the rate at which it does so; by definition, bioavailability is 1 (100%) for an intravenous dose.