Advantages – no polymorphism, short interval between softening & melting, storage at high temperature
Water soluble – dissolve slowly
Cause irritation because take up some water and cause dehydration of mucosa
Melting temperature much higher than body temperature
i.e. PEG
o
Can blend several to get the right melting range
o
Incompatible with many drugs
o
Common for vaginal administration
i.e. glycerin – causes defecation reflex and don’t get any drug absorption
Formulation Factors
Particle size – small (< 180 microns) to prevent irritation and consider solubility
Don’t worry about particle size if drug and base are incompatible
Presence of water – oxidation, hydrolysis, may need preservative, could precipitate if evaporates
Viscosity – matters in the mold so you don’t get settling; low = BAD
Hygroscopicity – if they absorb water, they dissolve; extra careful with these
Rate of drug release – depends on liquefaction and solution times & hydrophilicity/hydrophobicity of the drug
Brittleness – can be broken if they arne’t good or don’t have enough water
Volume contraction – contract at low volumes
Incompatibilities – many incompatible in PEG or crystallize in other bases
Rancidity/antioxidants
Antimicrobial preservative – add if aqueous phase is present
Density – calculate with density factor and cocoa butter being the average
