Modification of surface prop for h.phobic drugs Flashcards
why do we need to modify the surface properties of hydrophobic drugs?
because of its associated problems:
- poor aq solubility
- adhesion/ agglomeration
- poor dissolution rate/ bioavailability
- poor powder flow and poor drug content uniformity
what is the limiting step in the absorption of hydrophobic drugs?
In the absorption of hydrophobic drugs, the dissolution rate is the rate limiting step from Noyes-Whitney equation
what happens if you decrease aggregation of a hydrophobic drug?
the surface area increases, improves wetting and dissolution rate
why do we want to modify the surface properties of hydrophobic drugs?
to improve wetting, dissolution rate and hence bioavailability
what are the different techniques used to improve wetting, dissolution and bioavailability of poorly-water soluble drugs
- solid dispersion formulations
-surface adsorption of surfactants and polymers
complexation
particle size reduction
alternative polymorphic form
interactive powder mix
what is solid dispersions?
the incorporation of poorly-water soluble drugs in inert water soluble carriers
what is the aim of solid dispersion?
Is to alter the crystallinity of the drug in an attempt to enhance: dissolution ratein vivo absorptionsolubility wettability
when is solid dispersion mostly used?
is used as a way for improving the bioavailability of poorly water soluble drugs
give examples of carriers( excipients)
acids such as citric and succinic acids
sugars such as: xylitollactose and mannitol
polymers such as: polyethylene glycol and polyvinyl pyrrolidone
surfactants for example poloxamers
bile salts
urea
what are the two common methods of preparing solid dispersions?
1- melting ( fusion) method
2- solvent ( co-precipitation) method
what is the melting method?
The drug and the excipient are melted and the molten mass is cooled rapidly. The formed solid requires grinding; the drug and the excipient must have an acceptably thermal stability.
what is the solvent method?
the drug and the carrier are dissolved in a suitable solvent, which is then evaporated rapidly to dryness. The resulting solid mass needs grinding.
what are other possible methods of solid dispersions?
spray drying/ melt granulation/ lyophilization /freeze drying/ microwave irrdaitation/
co-precipitation/ kinetisol/ electrospinning/ hot melt extrusion
what are the 3 main types of solid dispersions?
Two-component crystalline dispersion, NO mixed crystals
Two-component crystalline dispersion, mixed crystals
Non-crystalline dispersion (amorphous or glassy systems)
what is eutectic mixtures?
For pharmaceutical uses, they are formed from drug substances and a water-soluble carrier.