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What are gels?
- Gels are semisolid systems consisting of dispersion of small inorganic particles or large organic molecules interpenetrated by a liquid
- Gels are semirigid systems in which the movement of the dispersing medium is restricted by an interlacing three-dimensional network of particles or solvated macromolecules of the dispersed phase
Gels are use for for delievering drugs to where?
- *Gels are compatible with many different drugs
What is a benefit of preparation of gels?
Relatively easy to prepare and very efficacious
Taking up of liquid with no measurable increase in volume
Taking up of liquid with increase in volume (solvation)
Intense interaction between particles of the dispersed phase so that, on standing, the dispersion medium is squeezed out in droplets and the gel shrinks (instability)
Reversible gel-sol formation with no change in volume or temperature (sol- liquid form of a gel upon agitation
removal of the liquid from a gel, leaving only the framework- eg. gelatin sheets, acacia tears, tragacanth ribbons
Should preservatives be used with gels? If so, which ones?
- Sodium Benzoate
- Benzalkonium chloride
What color should gels be?
- May be clear as water
- Others may be turbid
What are most gels?
- Most gels are water washable, water-soluble, water absorbing and greaselsee
- *but some have continuous phase alcoholic or oleaginous
What is the concentration of gelling agents generally?
Usually 0.5-2% (<10% of formulation)
What is a mucilage?
Single-phase gels made from synthetic or natural macromolecules
What is a single-phase system?
- Gels that contain linear or branched polymer macromolecules that dissolve in water and have no apparent boundary with the dispersing medium
- Natural polymers
- Semisynthetic cellulose derivatives
- Synthetic polyers
Example of a natural polymer
Example of a semisynthetic cellulose derivative
Example of synthetic polymers
Gels and magmas are why type of dispersion system?
What is a two-phase system?
- Gels that contain samll, descrete particles
- Are thixotropic (semisolid on standing but liquid when shaken)
What are magmas?
Two phase systems with large particle size or floccules of small distinct particles
Another name for magma?
What is an example of a two-phase system gel?
Aluminum hydroxide gel
What is an example of a magma?
What are some common gelling agents?
- xanthan gum
- alginic acid (seaweed)
- animal/vegatable fats: lard, cocoa butter
- Bentonite, Veegum (magnesium aluminum silicate)
- Carboxymethylcellulose (CMC) and other cellulose derivatives (methylcellulose, sodium-carboxymethylcellulose (CMC), Pluronic F-127)
- Carbomer resins (Carbopols)
- Carbowax bases (PEG ointment)
- Colloidal silicon dioxide
- Polyvinyl alcohol (PVA)
- Petrolatum, mineral oil/polyethylene gel, plastibase (jelene)
What are neutralizers used for?
Thicken the gel after the gelling agent is dispersed
What neutralizers are used with dispersions of less than 20% alcohol?
What neutralizer is used with dispersion up to 50% alcohol?
What are some neutralizers that can be used
- Na and K hydroxide
- Sodium Carbonate
The high water content of gels and magmas fosters what?
Support growth of bacteria, mold, and fungi
How should a preservative be chosen?
Use preservatives that do not afferct the gelling agent's efficacy
If the active drug doesn't interfere with the gelling process when should it be added?
The active drug should be added prior to gelling for uniformity of dispersion
If the active drug interferes with the gelling process what should be done?
place gel and active ingredient in plastic bag, then knead this to throughly mix the drug, the cut corner of bag to transfer gel into final container
What is the continuous phase of most gels?
- *can be alcoholic or oleaginous
How are gelling agents added?
Sprinkled in small portions on the surface of aqueous liquid
What things should be prepared through the use of hot water?
Bentonite and gelatin containing
What types of things should be prepared with the use of cold water and heat?
- Colloidal silicon dioxide
What are the benefits of stirring/sonication?
- Most gelling agents disperse faster with rapid stirring or sonication (sonication also removes air bubbles)
- *EXCEPTION Benotonie (added to non-agitated water)
What can be used to pre-wet the gelling agent to prevent clumping?
- Propylene glycol
- Other wetting agents
How is fastest dispersion achieved?
By slowly sprinkling very small particles of power into a rapid stirring liquid?
What is used to insure small particles enter?
What important information about topical dosage form should be given?
- For external use only
- Bandage only is prescribed, best to have open to the atmosphere whenever possible