40 Questions
What is the title form designated by the USP for a prepared suspension that requires reconstitution at the time of dispensing?
For Oral Suspension
Why are suspensions preferred over solid forms of the same drug for certain patients?
Because of the ease of swallowing and flexibility in administration of a range of doses
What is a disadvantage of certain drugs in solution form that is overcome when administered as undissolved particles of an oral suspension?
Unpleasant taste
Why are insoluble forms of drugs used in suspensions?
To reduce the difficulty of taste-masking
What is the primary consideration in selecting flavorants for an oral suspension?
Taste preference of the intended patient
What is the typical diameter of particles in a pharmaceutical suspension?
Between 0.1 µm and 10 µm
What is a characteristic of most oral suspensions?
They are aqueous preparations flavored and sweetened to suit patient preferences
What is the main difference between a colloid and a coarse dispersion?
The size of the particles
Why are some drugs supplied as dry powder mixtures for reconstitution?
Because they are unstable in the presence of an aqueous vehicle
Why are oral suspensions preferred for certain patient populations?
Because they offer a range of dosing options and ease of swallowing
What is the result of using erythromycin estolate in an oral suspension?
A palatable liquid dosage form of erythromycin
What is the purpose of suspending and dispersing agents in dry powder mixtures?
To facilitate the dispersion of the drug in the vehicle
What is the typical appearance of a pharmaceutical suspension?
Cloudy or opaque
What is a pharmaceutical suspension?
A liquid system in which the solid material remains as solid particles
What is the typical vehicle used for reconstitution of dry powder mixtures?
Purified water
What is the term used to describe the dispersion of a solid material in a liquid?
Dispersion
What is the proportionality constant in Newton's equation for the flow of a liquid?
Coefficient of viscosity
What is the characteristic of non-Newtonian liquids?
They have complex rheological behavior
What is the behavior of a substance in plastic flow below the yield value?
It behaves like an elastic body
What is the significance of the yield value in plastic flow?
It represents the stress required to break the inter-particular contacts
What is the characteristic of pseudo-plastic flow?
The curve starts from the origin and the viscosity cannot be expressed by a single value
What is an example of a liquid that exhibits pseudo-plastic flow?
Methyl cellulose in water
What happens to the volume of a dilatant liquid when shear stress is applied?
It increases
What is the relationship between shear stress and shear rate in dilatant flow?
The resistance to flow increases with increase in shear rate
What is the minimum percentage of solids required in a suspension to observe dilatant flow?
50% v/v
What is thixotropy?
The isothermal slow reversible conversion of gel to sol
What is the primary function of a suspending agent?
To keep finely divided insoluble materials suspended in a liquid media
Why is it important to consider the acid environment of the stomach when selecting a suspending agent for oral preparations?
Because it may alter the physical characteristics of the suspension
What is a characteristic of a good suspension?
It has high viscosity at rest and low viscosity when agitated
Which of the following is an example of a natural suspending agent?
Gelatin
What is the purpose of a suspending agent forming a film around particles?
To decrease interparticle attraction
What is a consideration that applies to suspensions in terms of stability?
Both physical and chemical stability considerations apply
What is the primary concern for the chemical stability of a drug?
To ensure the drug remains effective over its intended shelf-life
How is the effect of temperature on the chemical stability of a drug established?
By testing the drug at different temperatures
What is the ideal outcome for sedimentation in suspension formulations?
To minimize sedimentation
How should the patient or care taker re-disperse the sediment in a suspension formulation?
By gentle shaking and inversion of the bottle
What is the purpose of assessing the particle size distribution and drug content of representative samples?
To measure the physical stability of the suspension formulation
Why are specifications set for the maximum permitted levels of specified degradation products?
To ensure safety considerations are met
What is the limitation of visual assessment of sediment redispersion on shaking?
It can only provide a general indication of whether there is a problem or not
What should be consistent across depth and over time in a suspension formulation?
The particle size distribution and drug content
Study Notes
Pharmaceutical Suspensions
- A pharmaceutical suspension is a coarse dispersion of insoluble particles (> 1 µm in diameter) in a liquid medium, usually aqueous.
- The solid material (usually the drug) does not dissolve in the vehicle to any appreciable extent but remains as solid particles distributed throughout the vehicle.
- Pharmaceutical suspensions fall across the borderline between colloidal and coarse dispersions, with solid particles generally in the range of 0.1 to 10 µm.
Reasons for Suspensions
- Certain drugs are chemically unstable in solution but stable when suspended.
- Suspensions ensure chemical stability while permitting liquid therapy.
- The liquid form is preferred to the solid form for ease of swallowing and flexibility in administration of a range of doses.
- Suspensions overcome the disadvantage of a disagreeable taste of certain drugs.
Features Desired in a Pharmaceutical Suspension
- Newton's equation for the flow of a liquid: S = ηD (shear stress is directly proportional to shear rate)
- Non-Newtonian flow: emulsions, suspensions, and semisolids have complex rheological behavior and do not obey Newton's law of flow.
- Types of non-Newtonian flow: plastic flow, pseudo-plastic flow, and dilatant flow.
Suspending Agents
- Suspending agents are substances that prevent agglomeration of finely divided insoluble materials and impart viscosity to the dispersion media.
- Suspending agents form a film around particles and decrease interparticle attraction.
- A good suspension should have well-developed thixotropy.
Classification of Suspending Agents
- Natural: animal origin (gelatin), plant origin (acacia, tragacanth, starch, seaweed), and mineral sources (bentonite, kaoline).
- Semi-synthetic: substituted cellulos (hydroxyethyl cellulose, sodium carboxymethylcellulose, methylcellulose, microcrystalline cellulose).
- Synthetic: synthetic polymers (carboxypolymethylene, polyvinyl alcohol, polyvinyl pyrrolidone iodine complex).
Suspension Stability
- Chemical stability: the drug must remain chemically stable over the intended shelf-life of the product.
- Physical stability: sedimentation should be kept to a minimum, and easy redispersion of the sediment is necessary.
- Redispersion pattern should be established, testing at suitable time intervals and under various storage conditions.
This quiz covers the basics of pharmaceutical suspensions, including their definition, characteristics, and composition. Learn about the properties of suspensions and how they differ from other liquid systems.
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