Jan 19 - Powder Dose Forms Flashcards
What does the term “powder” refer to?
It may refer to the physical state or the finished product
What are powders?
Powders are intimate mixtures of finely divided drug or drug and excipient for internal or external use
What is micromeritics?
The science of small particles and includes:
- particle size, distribution and shape
- angle of repose, porosity, true and bulk volume
- tapped and apparent density
What does particle size and shape influence?
They influence factors such as dissolution rate, suspendability, uniformity, grittiness
What is small particle size associated with?
Larger surface area, faster dissolution, better suspendability
How does particle size and shape influence homogeneity?
Particles of similar shape and size tend to blend more uniformly and more homogenenous mixtures (homogeneity is very important for many dose forms)
How is particle size determined?
Sieving methods, microscopy, sedimentation rate, light scattering
How is particle shape determined?
Particle shape can be seen by microscopy or inferred through its angle of repose
What is the angle of repose?
Simplistically, the powder is allowed to flow through a funnel and fall freely onto a surface. The height and diameter of the resulting cone are measured and the angle of repose is calculated by : tan theta = h/r
How is the angle of repose related to the flow properties?
Powders with a low angle of repose flow freely
Angles over 50 degrees have poor flow
How does particle shape influence flow?
The more spherical and smooth the particles are, the better the flow
Poor flow with more irregular shape and roughness (rugosity)
Poor flow with crystalloid needles or plates
What is ratholing of a funnel?
It is when particles stick to the sides of a funnel
What is bridging (arching) of a funnel?
When the flow stops completely (the particles don’t flow through the spout of the funnel)
What is flooding of a funnel?
The particles stick to each other they stick to the funnel (the particles fill the funnel and the spout)
What is true density?
It is the weight per unit volume
What affects apparent and tapped density?
They are affected by particle size and shape. With larger rougher particles, there are more spaces in between them and an apparent larger volume per unit of mass. This has implications for dose forms like capsules, where volume is fixed
What is comminution?
The process of reducing particle size of a solid
What are some of the methods used for comminution?
Trituration with a mortar and pestle (simultaneously reduce and make size uniform)
Levitigation with a spatula
Levitigation with a mortar and pestle (useful technique for preparing suspensions)
When powders are to be combined into a homogeneous mixture, it is important all the particles are about the same size. Why?
Powders with different particle size stratify or segregate and do no remain homogenous
When do eutectic mixtures occur?
When the melting point of the mixed materials is depressed to the point of liquefication.
What factors influence the occurrence of eutectic mixtures?
It depends on the proportions of materials, use of trituration and presence of adsorbant material
Give some examples of materials that tend to form eutectic mixtures?
Acetaminophen, aminopyrine, aspirin, benzocaine, camphor, chloral hydrate, lidocaine, menthol, phenol, phenylsalicylate, prilocaine, resorcinol, salicylic acid, thymol, urea
What are the two strategies for dealing with eutectic mixtures?
- Allow the eutectic to form by triturating. Add an absorbing inert material until the mix is powder-like (use calcium, magnesium oxide, talc, etc)
- Mix the components separately with a suitable diluent. Combine the protected materials. Add remaining materials using geometric dilution
Some powders may be designed for external use. Explain
May be used as dusting powders
May be used as powder for dissolution followed by soaking or application
Some powders may be designed for internal use. Explain
May be incorporated into tablets, capsules or powder papers
May also be bulk for internal use (e.g. Metamucil)
Name the different types of containers available for topical powders (depending on the application)
Yorker spout cap
Disc-top cap
Flip-top cap
Shaker-top cap
What are some of the advantages of having a product in the solid state
Increased stability (most drugs)
Flexible
Convenient
Having products in the solid state offers some advantages, such as flexibility. Explain
A number of different dose forms can be fabricated and each dose form can contain a different amount of drug
Allows for controlled release (if necessary)
Having products in the solid state offers some advantages, such as convenience. Explain
Solid dose forms are usually easily administered
They are also easy to package and ship
What are bulk powders?
Non-potent medications which can be dosed with acceptable accuracy using kitchen teaspoons and tablespoons.
What are bulk powders used for?
They can be orally administered powders, usually dietary supplements, antacids and laxatives. These are usually mixed into juice or water prior to oral administration.
They can be powders for external use dusted onto the skin using a sift-top container. These often contain an active ingredient such as a topical fungicide and a diluent or vehicle powder
What is a divided powder?
A single dose of powdered medication wrapped in paper or foil-plastic laminates. This extemporaneous dose form is useful for medications for young children and elderly. It delivers an accurate quantity of medication and can be used for potent drugs.
How is a divided powder dose form administered?
The powder consists of an active drug uniformly distributed in a soluble diluent like lactose. The contents of the paper are dissolved in water or juice just prior to administration
What are granulations?
Coarse particles made by blending powders then moistening to form a pasty mass. The mass is passed through a sieve and formed granules are allowed to air-dry
What are granulations used for?
Used in preparation of tablets and sometimes capsules (granules have good flow properties compared to powders. Can also be used for non-potent drugs as bulk preparation where teaspoon or tablespoon used to measure and product dissolved/dispersed in water or juice
How are effervescent granules made?
Effervescent granules can be made by mixing granules made with citric and tartaric acids (1:2) with granules made with sodium bicarbonate (it is more common to see pressed into an effervescent tablet like Alka-Seltzer
What is the function of aluminum hydroxide?
Antacid
What is the function of magnesium trisilicate?
Antacid
What is the function of peppermint oil?
Flavor, scent
What is the function of calcium carbonate?
Antacid
What is the function of benzocaine?
Local anesthetic
What is the function of salicylic acid?
Keratolytic
What is the function of benzoic acid?
Antifungal agent
What is the function of camphor?
Antipruretic (anti-itching)
What is the function of methyl salicylate?
Scent
What is the function of talc?
Adsorbant, vehicle
What is the function of mercaptopurine?
Antineoplastic
What is the function of lactose?
Diluent, filler
