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54 Cards in this Set

  • Front
  • Back

What is a suspension (by definition)?

A coarse disperse system where an insoluble solid is dispersed in a liquid medium

What is the disperse phase made of?

Solid particles, usually > 0.1µm

What is the disperse medium made of?

Aqueous media


(Infrequently also organic or oil)

What are the reasons for formulating a suspension?

-Drug is predominantly insoluble


-Drug is more stable in suspension


-Need to control the rate of release of the drug


-Drug has bad taste> helps to improve compliance by masking taste


-Easy to swallow


-Can divide and control the dose


-Fast pharmaceutical action

List some examples of oral suspensions

Aluminium hydroxide or magnesium hydroxide antacid suspensions

State an example of a parenteral suspension

Insulin zinc suspension BP

State an example of a topical application

Calamine lotion BP

State an example of dry powder for suspensions

Barium Sulphate for suspension BP

Why can prednisolone be put in suspension?

It's poorly soluble

Why is Oxytetracycline put in suspensions?

To prevent degradation of drug/ to improve stability of the drug

Why is Chloramphenicol Palmitate put in suspension?

To mask the taste, it's bitter/unpleasant

Why is calamine lotion put in suspension?

For use as a topical applicant

Why are penicillin and procaine put in suspension?

To control the rate of drug absorption (Parenteral application)

Give an example of a vaccine put in suspension

Cholera vaccine

Which x-ray contrast agent is formulated as a suspension?

Barium Sulphate

What are the desirable properties of suspensions?

-Dispersed particles should settle slowly, allowing accurate and uniform dose


-The particles should remain flocculated and be readily dispersed upon shaking (caking/aggregation should be avoided)


-Ease of use: viscosity, product must be easily dispersed from its container


-Particle size: should remain reasonably constant to assist stability and re-dispersion


What does particle size affect?

-Dose uniformity


-Variable dissolution and bioavailability


-Sedimentation (physical stability)


-Texture (larger particles over 5µm in diameter give gritty texture)

Which law do particles follow during sedimentation?

Stoke's Law


What is the sedimentation volume, F, defined as?

The raito of the Height of the sediment/Height of the whole pharmaceutical product


Vu/Vo

Why do powders float on top of liquids?

-Presence of an absrobed layer of air


-The lipophilic nature of certain materials or contaminants


-Poor properties of "wettability"- this generally refers to the contact angle of the particle and the surface

What are the properties of hydrophobic powders?

-Have high contact angle


-Not easily wetted and tend to float on the surface of the liquid


(eg: sulphur or magnesium stearate)

What are the properties of hydrophilic powders?

-Low contact angle


-Readily wetted


(eg zinc oxide or magnesium carbonate)

How can you improve particle wetting?

Use wetting agents. This improves wettability of hydrophobic powders by reducing surface tension between the particle and the liquid surface, and therefore reducing the contact angle

Why must particles be wetted for suspensions?

Only wettable and wetted particles can be readily dispersed into the liquid and remain adequately dispersed

Which wetting agents are used for oral suspensions?

Surfactants such as polysorbates sorbitan esters (Tweens and Spans)

Which wetting agents are used for IV suspensions?

Lecithin, polysorbates and poloxamers and related materials

In what concentrations are wetting agents used?

Used in relatively low (ca. 0.1% w/w) concentrations

What is a disadvanatge of wetting agents?

They may cause excessive foaming in product

What are some examples of hydrophilic colloids?

Acacia, bentonite, tragacanth, alginates, xantham gum and carious celluose derivatives


What are hydrophilic colloids used for?

-Used to coat particles to make them more wettable


-Act as suspending agents due to their viscosity

Which solvents are used to improve particle wetting?

Various alcohols (usually ethanol), glycerol and glycols

What are solvents used for in suspensions?

To penetrate into loose aggregations of particles to displace the air adsorbed within such structures

What is the definition of flocculation?

A process of contact and adhesion whereby the particles of a dispersion form larger-size clusters

What is flocculation?

The removal of a sediment from a fluid. Flocculation can be forced through agitation or the addition of flocculating agents

Flocculation vs Deflocculation

What is the equation for sedimentation volume in a deflocculated system?

Fu = Vu/V0

What is the equation for sedimentation volume in a flocculated system?

Ff = Vf/V0

What is the equation for the degree of flocculation?

β = Ff/Fu = Vf/Vu

What does a bigger value of β mean?

Better flocculation

What is Zeta potential?

The electrical potential in the interfaical double layer at the boundary of different regions of a suspension. The potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle in suspension.

What happens if the concentration of electrolytes in suspension is too high?

Results in charge repulsion and therefore caking of the suspended agent

How is flocculation in suspension controlled?

By buffering the formulation to control the pH and ionisation, and by controlling the electrolyte concentration

Which polymers are used in suspensions?

Starch, alginates, tragacanth, and cellulose derivatives

Give two examples of polysaccharides and when they're used

-Acacia: used with other thickeners in extemporaneous products


-Tragacanth: used in extemporaneous products, slow to hydrate, and shows non-Newtonian behaviour

List different types of viscosity modifiers

-Polysaccharides


-Alginates


-Water-soluble celluloses


-Hydrated silicates


-Carbomers

Why are hydrated silicates used to modify viscosity?

They're highly absorbent and Non-Newtonian

What additives are added to suspensions to improve compliance and shelf life?

-Buffering agents


-Sweeteners


-Flavours


-Colouring agents


-Preservatives

Which methods can be used to manufacture suspensions?

-Extemporaneous methods eg: mortar and pestle


-High-shear mixers


-Homogenisers


-Ball mills


What is the definition of Ostwald Ripening?

The change of an inhomogeneous structure over time. Over time, small crystals (or sol particles) dissolve, and redeposit onto larger crystals or sol particles.

What is the equation for the solubility of particles?

How many common crystal forms does cortisone acetate suspension have? How many of these are unstable, and how do they change into the stable form?

Five common crystal forms


Four unstable> turn to stable form in presence of water


(caking is often observed when the crystal form changes)

Which additives or conditions can cause the inhibition of crystal growth?

-Polymers> form a prtoective layer around the particles


-Surfactants>reduce crystallisation (some may increase it)


-Temperature> influences solubility, which changes the degree of saturation or supersaturation in solution

Which tests are carried out to evaluate physical stability?

-Aesthetic tests (appearance, colour, odour, taste)


-pH (zeta potential and solubility)


-Sedimentation rate


-Particle size and form


-Redispersion and centrifugation tests


-Rheological measurements


-Freeze-Thaw temperature cycling


-Compatability with container and cap liner


-Dose uniformity


-Microbial testing

What excipients are in calamine lotion, and why?

-Calamine 30g


-Zinc oxide 10g-Bentonite 6g (thickening agent)-Sodium citrate 1g (controls flocculation)-Liquefied phenol 0.5mL (preservative)-Glycerol 5mL (thickening agent; also helps the product adhere better to the skin)-Water to 200mL