Dosage Forms

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powder

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intimate mixtures of dry finely divided drugs with/without excipients and can be used either internally or externally

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advantages of powders

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1. wide choice of ingredients and dosage can be easily achieved for patient administration
2. increased stability as compared to solution
3. large dose which can't be administered in other forms, can be administered as powder
4. a rapid dispersion of drugs occurs in stomach when given in powder forms than in compressed form
5. powder can be dispersed in water or another liquid and more easily swallowed

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limitations of powder

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1. if taste of drug isn't good, powder isn't the dosage form of choice
2. drugs which deterioate readily in exposure to atmosphere should not be dispensed as powders

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4 methods to mix powders

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1. trituration
2. spatulation
3. sifting
4. tumbling

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trituration

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mixed with mortal and pestle

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two types of mortal and pestle

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1. wedgewood mortar used for pulverizing and grinding because of rough inner surface
2. glass mortar used for simple mixing and mixing colored materials and dyes

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spatulation

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powder spatula is used and powders are mixed on a pill tile
-adequate for mixing small amounts of powders and combinations of powders having same densities

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sifting

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helpful for powders that resist mixing by trituration

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examples of powders undergo sifting

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very light powders like magnesium oxide and charcoal can be completely mixed by shaking them through a sieve

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tumbling

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mixing powders by shaking or rotating them in a closed container - used where two+ extremely light powders are being combined

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problems encountered during mixing

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1. crystalline salts are mixed best by trituration in mortar - surface of mortar grows smooth
2. electrification
3. packing
4. physical immiscibility
5. dampening or liquefaction

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electrification

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substance repels each other when mixed
-due to resistance to admixture or electrical charges

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packing

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powders are pressed heavily during trituration
-avoided by triturating lightly and scraping sides of mortar frequently with spatula

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physical immiscibility examples

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-mixing resinous materials with granular salts
-mixing heavy powder with a light one

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dampening or liquefaction (3 reasons occurs)

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-most troublesome problem, why occurs:
1. by absorption of moisture from air (deliquesent or hydroscopic)
2. giving up moisture to the air and liquefy during process
3. lowering the melting point of mixture (eutectic mixture)

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eutectic mixtures

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certain organic compounds (phenol, aldehydes, ketones) are mixed with varying proportions

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two ways to handle eutectic mixtures

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1. mixing each compound with equal amount of inert diluent (lactose, starch, talc) and combing diluted powders with light trituration
2. mixing materials together and allow to liquefy and adding sufficient diluent to absorb the eutectic mixture and remain as a powder

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three basic rules of mixing powders

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1. when there are different physical states (granular salts and fine powders) reduce each powder separately to fine particles before mixing
2. when mixing powder with different densities put the light powder first and then the heavier one on it
3. when mixing small amounts of drug to a bulk of powder, use geometric dilution

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geometric dilution

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small weight of drug is first triturated with equal bulk of diluting powder
-next mixed with equal amounts of diluent
-process repeated until all powders are intimately mixed

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classification of powders

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1. bulk powders
2. divided powders
3. special powders

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bulk powders

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patient measures out their own dose

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examples of bulk powder

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-dusting powder
-powders used internally
-powders used for making solution
-powders used for inhalation

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divided powders

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single doses of powdered drug mixtures individually enclosed in paper, cellophane, or metallic foil wrappers/packets

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special powders

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1. effervascent salt
2. dentifrices
3. insufflations
4. powder aerosols

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effervascent salt

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powders/granules containing sodium bicarbonate, a suitable organic acid or inorganic acid and medicinal agents
-when mixed with water, the acid and base react to form carbon dioxide

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advantages of effervascent salt

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1. mask unpleasant taste of drugs
2. carbon dioxide stimulates the flow of gastric juice and also accelerate absorption of many drugs
3. favorable psychological effect on patient
4. stability is enhanced since stored in low moisture content packages

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preparation of effervascent salt (2)

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1. heat method
2. wet method

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heat method of preparation of effervascent salt

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blending of all components with the inclusion of 15-20% of acid ingredient as citric acid monohydrate and heated on a bath
-mole of water released from citric acid during heating moisten powder and granules are formed from moisten powder mass

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wet method of preparation of effervascent salt

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critic acid is moistened and added to sodium bicarbonate
-granules are formed from partially fused mass

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dusting powders

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powders used for external use only

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properties of dusting powders

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1. homogeneous
2. free from local irritation
3. free flowing
4. uniform spreading and covering capability
5. good adsorptive and absorptive capability

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dentrifrices

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powders which are used to clean teeth

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insufflations

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finely divided powders intended for application to body cavities such as tooth sockets, ear, nose, throat, etc

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powder aerosols

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dispensed as aerosols in pressurized push button containers

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examples of powder aerosols

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antiperspirants and deodorants