liquid dosage forms

definition of logP

ratio of a drug’s concentration in a lipophobic solvent to its conc in water at eqm

logP

log( [drug]_octanol / [drug]_water )

how does crystal/solid properties affect solubility

STRONGER INTERACTIONS in the solid lattice = higher mps and LOWER SOLUBILITY

how do solute-solvent interactions affect solubility

HIGHER number + STRONGER s-s interations = INCREASED SOLUBILITY

how does ionisation state affect solubility

molecules bearing a NET CHANGE (ionic) are normally MORE SOLUABLE in water

how does pH affect solubility

pH in formulations is adjusted to INCREASE DRUG IONISATION = INCREASED SOLUBILITY

viscosity

measure of a liquid’s resistance to flow: influenced by temperature and composition.

vapour pressure of an ideal solution is dependant on

the vapour pressure of each chemical component and the mole fraction of the component present in the solution

raoult’s law for vapour pressure

Pi = Pi^° * Xi

high logP (+ve)

higher conc in lipid-rich tissues = improved oral bioavailabilty

low logP (-ve)

lower conc in lipid-rich tissues = reduced oral bioavailabilty

methods to accelerate dissolution

• particle size reduction

• solution stirring

• increased temperature

how does temperature affect solubility

increased temp = higher solubility (no gases)

eqm vapour pressure is

pressure exerted by a vapour in thermodynamic eqm with its corresponding liquid at a given temperature in a closed system

high vapour pressure =

higher evaporation = more volatile

how does adding non-volatile liquid to a water affect vapour pressure

decreased = fewer water molecules to vapourise

how does solution stirring affect solubility

REDUCES boundary layer tightness = ENHANCED drug diffusion = INCREASED solubility