Provide examples of liquid and semi-solid dosage forms?
- Solutions
- Supsensions
- Ointments
- Creams
What are suspensions?
-A coarse disperse system where an insoluble solid is dispersed in a liquid medium
What is the dispersed phase in most pharmaceutical applications?
-Usually aqueous media or it may infrequently be an organic or oily material
Why do we need suspensions?
- When drug is predominately insoluble
- Drugs are more stable in a suspension or an emulsion than in another dosage form (stability)
- There may be need to control the rate of release of the drug
- When drug has bad taste if taken orally (compliance)
What are the different types of suspensions and provide examples for each?
- Oral suspensions e.g Alumminium hydroxide
- Parenteral suspensions e.g insulin zinc suspension
- Topical suspensions - e.g Calamine lotion
- Dry powder for suspensions e.g Barium sulphate suspension
What are the desirable properties of suspensions?
- The dispersed particles should settle slowly (this allows for accurate and unifromity dose to be taken from medicine
- The particles should remain flocculated (evenly distributed throughout the liquid media and should readily dispersed upon shaking)
- Caking should be avoided - for uniformity of drug distribution and physical stability
- Ease of use - viscosity should be appropriate
- Particle size - should remain reasonably constant, this assists stability and re-dispersion
Controlling particles size controls what?
- Texture
- Dose uniformity
- Variable dissolution and bioavailability
- Sedimentation
Partciles will fall under the force of gravity according to stokes law. TRUE OR FALSE?
TRUE
According to stoke’s law, what physical properties influence sedimentation?
- particle size
- Viscosity
What causes powders to float on top of a liquid?
- Due the presence of an abosrbed layer of air
- The lipophilic nature of certain materials or contamiants
- Poor properties of wettability - referes to contact angle of particles and the surface
Hydrophobic powders have a high contact angle, they are not easily wetted and tend to float on the surface of the liquid. TRUE OR FALSE?
TRUE
Provide two examples of hydrophobic powders?
- Sulphur
- Magnesium stearate
Hydrophilic powders tend to have low contact angle. TRUE OR FALSE?
TRUE
Hydrophilic powders are readily wettable. TRUE OR FALSE?
TRUE
Give two examples of hydrophilic powder?
- Zinc oxide
- Magnesium carbonate
How to the addition of wetting agents improve particle wetting?
-They improve the wettability of hydrophobic powders by reducing surface tension between the particle and the liquid surface as well as reducing surface contact angle
Only wettable and wetted particles can be readily dispersed into the liquid and remain adequately dispersed. TRUE OR FALSE?
TRUE
Give examples of surfactants used in oral and i.v route in improving particle wettability?
- Oral - the use of tweens and spans
- I.V - Lecithin and polysorbates
What is one disadvantage that comes with using surfactants for oral and i.v route to improve particle wettability?
- They may cause excessive foaming in the product
Provide examples of hydrophilic colloids that are used to improve particle wettability?
-Acacia,bentonite
Particles that are intended for suspension generally do not become more wettable after being coated with a layer of hydrophilic colloid. TRUE OR FALSE?
FALSE
Hydrophilic colloids also acts as suspending agents, as a result of their viscosity. TRUE OR FALSE?
TRUE
Give examples of solvents used to improve particle wettability?
- Various alcohols (ethanol)
- Glycerol, glycols
What is the IUPAC definition for flocculation?
It is a process of contact and adhesion whereby the particles of a dispersion form large size clusters
