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- Emulsifying agents
- Wetting agents
- ex. polysorbate 20
- To promote and maintain dispersion of finely subdivided particles of liquid in a vehicle in which it is immiscible (oil and water)
- ex. Sodium lauryl sulfate, lanolin, cetyl ROH, acacia, Glyceryl monostearate
- Aid in attaining intimate contact between solid particles and a liquid
- ex. Polysorbate, Sodium lauryl sulfate, Benzalkonium chloride
- Liquid used as an intervening agent to reduce the particle size of a powder by grinding (usually in a mortar)- makes paste usually
- Mineral oil, glycerin, propylene glycol
- Used to increase thickness or hardness of a preparation
- (i.e. ointments)
- ex. Ceresin, Stearyl alcohol
- Used to soften the skin and make it more pliable
- ex. Mineral Oil, petrolatum, lanolin
- Used to provide an acidic medium for product stability
- ex. Citric acid – also used as an antioxidant, buffering agent, chelating agent, and flavor enhancer
- Used to resist change in pH upon dilution or addition of acidic or alkali agents
- ex. Potassium phosphate, monobasic, and sodium acetate
- Inert filler to create desired bulk and flow properties
- Also aids in compression characteristics of tablets and capsules
- ex. lactose, mannitol, sorbitol, starch
- Used in liquid and semisolid preparations to prevent growth of microorganisms
- ex. Imidurea, sodium acetate, sodium benzoate, parabens, ROH
- Used to render preparations more resistant to flow
- • In suspensions to deter sedimentation
- • In ophthalmic solutions to increase contact time
- • To thicken topical creams
- ex. Carbomer – gelling agent
- Scientific study of deformation and flow properties of matter
- Applied to solids, liquids and gases
Rheology describes consistency of products based on ...
viscosity and elasticity
Measure of resistance to flow or thickness
- Measure of stretchiness or structure
- Predominantly solid feature
Higher the viscosity...
greater the resistance of the material to flow
- Phenomenon observed in materials exhibiting both elastic behavior and viscous flow
- i.e. polymer gel, gelatin
Rheology plays an important role in...
dispensing and formulation of various dosage forms including emulsions, suspensions, creams, lotions and tablet coatings
Rheology helps us understand
- Passage through the orifices, including pouring, packaging in bottles
- Passage through hypodermic needles.
- Removal from jars and extrusion from tubes
- Spreading and adherence to the skin
- Capacity of solids to mix with miscible liquids
- Release of drug from the base
- Thixotropic materials become more fluid with increasing time of applied force (stirring, pumping, shaking)
- Often reversible
Thixotropic systems usually contain...
asymmetric particles that provide a loose three dimensional structure via numerous points of contact throughout the sample.
Describe Thixotropy at rest and when shear is applied:
- Rest: structure provides a degree of rigidity on the system that resembles a gel
- Shear applied: the structure begins to breakdown as points of contact are disrupted and particles become aligned.
- Study of deformation and flow in biological systems
- Biological fluids are viscoelastic materials that are rheologically complex
What is blood?
is a non-Newtonian fluid and rheological properties of blood are influenced by many pathological conditions
How are the flow properties of blood determined?
- by hematocrit (Hct) and plasma viscosity.
- Elevated Hct is associated with arteriosclerosis, angina, myocardial infarction.
Rheology of suspensions and emulsions:
Final product should be pourable or injectable
Rheology :Removal and spreading of ointments:
- Addition of pharmaceutical additives could change the properties of the ointment base.
- Removal from container esp. important in case of elderly patients
Rheology: Polymeric gels used in drug delivery:
Development of systems that gel in situ upon administration
- Used in preparations to provide alkaline medium for product stability
- ex. Triethanoloamine (trolamine)
Any component other than the active principle added intentionally to the medicinal formulation
Excipients contribute to...
- the physiochemical properties of pharmaceuticals
- Ensure the weight, consistency and volume necessary for proper dosage administration