Solubility of Drugs and Phase Rule Study Guide

Solubility

The concentration of a solute that dissolves in a specific volume of solvent at a defined temperature to create a homogenous solution.

Saturated Solution

A state where the dissolved solute in the solution exists in equilibrium with the solid phase.

USP-NF

Expresses solubility as the number of milliliters (ml) of solvent required to dissolve 1 part of solute.

Molarity (M)

The number of moles of solute contained in 1 liter of solution.

Biopharmaceutics Classification System (BCS)

Classification of drug substances based on aqueous solubility and intestinal permeability.

Polar Solvents

Solvents that possess high dielectric constants and solubilize ionic and polar substances via hydrogen bonding.

Hildebrand Parameter (δ)

A numerical value indicating the relative solvency behavior of a solvent.

Lipinski's Rule of Five

A rule to evaluate 'drug-likeness' for orally active drugs: MW ≤ 500 Da, HBD ≤ 5, HBA ≤ 10, Log P ≤ 5, PSA ≤ 140 Ų.

Diffusion

The net mass transfer of individual molecules from a region of high concentration to a region of low concentration.

Passive Diffusion

Movement along a gradient, typically suitable for sizes 100 to 500 Daltons.