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Semi Solid DFs, Routes of Administration, ointment, paste, cream, ideal properties of a base, characteristics of ointment bases & specific examples, general preparation methods of ointments

Semisolid dosage form

-has properties that are those between solid and liquid, used for external application of skin or mucous membranes
-systems in pharmacy include:
--ointments, solidified emulsions, creams
--gels, magmas, rigid foam
--pastes, plasters
-vast majority intended for topical applications - common sites are skin, eye, nose, vagina, and rectum
-mainly intended for local effect
-however, systemic absorption s/b taken into account when using topical products in pregnant/nursing mothers

topical

-dermatologic product designed to deliver a drug to the skin in treating dermal disorders, skin is the target organ

transdermal

-preparation designed to deliver drugs through the skin to the general circulation for systemic effect, skin is Not the target organ

ointments

semisolid preparations intended for external application to skin/mucous membrane
-medicated/non-medicated
-non-medicated provide protective & lubricating effects
-main formulation components are drug and ointment base

ointment base

the vehicle in which the drug is dispersed in ointments
-Four general groups
--oleaginous (hydrocarbon) bases
--absorption bases
--water-removal bases
--water-soluble bases

Oleaginous bases

(hydrocarbon) bases: protect skin against escape of moisture (emollient)
-remain on skin for longer period of time/effective as occlusive dressings
-difficult to wash (greasy/lipophilic)
-aqueous preparations may be incorporated
-Includes: Petrolatum (yellow petroleum/petroleum jelly), White petrolatum (white petroleum jelly), Yellow ointment, White ointment

Petrolatum

(yellow petroleum/petroleum jelly) - purified mixture of semisolid hydrocarbons obtained from petroleum. e.g. Vaseline
-oleaginous base

White Petrolatum

(white petroleum jelly) - decolorized petrolatum (aesthetic appeal)
-oleaginous base

Yellow ointment

mixture of petrolatum (950 g) & yellow wax (50 g)
-oleaginous base

White ointment

mixture of petrolatum & white wax
-oleaginous base

Absorption bases

can absorb appreciable quantities of water/aqueous solutions w/o marked changes in consistency
-Two types
--Emulsifiable bases
--Emulsion bases (w/o emulsions)

Emulsifiable bases

do not contain water but become w/o emulsions upon incorporation of water.
-ex. hydrophilic petrolatum (cholesterol, stearyl alcohol, white wax & white petrolatum)
-absorption base

Emulsion bases

w/o emulsions that permit incorporation of additional quantities of water.
-ex. lanolin (purified wax-like substance obtained from wool of sheep)
-absorption base

Water Removal bases

(aka Washable) bases: o/w emulsions, can easily be removed from skin - called water washable emulsions, can absorb serious discharges.
-ex. Hydrophilic ointment USP

Hydrophilic ointment

-example of water removable (washable) base
-contains following ingredients: methylparaben, propylparaben, sodium lauryl sulfate, propylene glycol, stearyl glycol, white petrolatum, purified water

Water Soluble Bases

(aka Greaseless) bases: no oleaginous bases, completely water washable, mostly used for incorporation of solid substances,
-polyethylene glycol (PEG) ointment is an example of water soluble base that contains PEG 3350 and PEG 400
<600 clear, colorless liquids
>1000 are wax-like white material
>600 and <1000 are semi-solids
PEG ointment NF formula: PEG 3350, 400 g & PEG 400, 600 g

ointment preparation

based on nature of ingredients, prepared by two methods - incorporation and fusion

Incorporation

-drug powder or water soluble drug is incorporated into small quantities of ointment base
-components mixed until uniform preparation attained
-extemporaneous preparation (mortar & pestle/spatula used to rub ingredients together on ointment slab/pill tile/parchment paper)
-large scale manufacturing (stainless steel tank w/ counter sweep agitation & built-in homogenizer, ointment roller mill)

incorporation of drug powder

-drug powder can be incorporated by using spatula/mortar & pestle
-drug material is levigated (process of grinding an insoluble substance to fine powder, while wet) with small amt of vehicle or miscible component of formulation to form a concentrate
-Mineral oil & PEG may be used as levigating agents (wetting agents)
-concentrate is mixed with remainder of the base

incorporation of liquids

-small quantity of aqueous solution may be incorporated in oleaginous bases
-if aqueous solution is to be added to oleaginous base, solution may first be mixed with small amt of hydrophilic base & then w/ oleaginous bsase
-up to certain limit, water soluble substances can be mixed w/ water soluble bases

Fusion

all or some of components are melted together & cooled w/ constant stirring
-components not being melted are added to congealing mixture as it is being cooled & stirred
-process of fusion can be conducted in beaker/porcelain dish
-for large scale manufacturing, fusion carried out in large steam-jacketed kettles
-once congealed, ointment is passed through ointment mill

Creams

semisolid emulsion systems that have a creamy appearance as the result of reflection of light
-one or more medications may be dispersed in either w/o or o/w emulsion
-ex. vanishing cream (o/w emulsion containing large percentage of water, stearic acid & other oleaginous components)
-Application - primary is topical skin products, rectal & vaginal products
--can be applied in weeping or oozing surfaces
--patient & physician-preferred - easier to spread & remove
--many drugs available as both creams & ointments

Pastes

semisolid preparations that contain a Larger Amount of Solids compared to ointments
-stiffer than ointments, remain in place after application & can absorb serious secretions
-ex. zinc oxide paste, contains 25% ZnO in starch & white petrolatum, product is firm & can protect skin & absorb secretion better than zinc oxide ointments

Packaging

_ of Semisolid Dosage Forms:
-Topical dermatological products in jars/tubes
-ophthalmic, nasal, vaginal & rectal products always in tubes
-ointment jars made of opaque glass/plastic
-tubes made of aluminum/plastic
-ophthalmic, rectal, vaginal, aural & nasal semisolid preparations are packaged w/ special applicator tip

Gels

semisolid systems in which movement of dispersed medium is restricted by interlacing three dimensional network of particles/solvated macormolecules of dispersed phase
-also defined as system of at least two constituents, consisting of condensed mass enclosing an interpenetrated by liquids
-when coherent matrix is rich in liquid, product often called jelly (ex. table jelly)
-when liquid is removed & only framework remains, gel is known as xerogel

Types of Gels

-Two phase gel vs. Single phase gel
-Inorganic gels vs. Organic gels

Two phase gels

(or magma)
-gel consists of floccules of small & distinct particles rather than large molecules
-gels are thixotropic (semisolid on standing but becomes liquid on agitation)
-includes inorganic gels

Single phase gels

when gel consists of macromolecules existing as twisted/matted strands, gel structure is called one phase system because no definite boundary exists between dispersed macromolecule & liquid
-network of gelling structure are held together by stronger van der Waals forces
-ex. tragacanth & carboxymethylcellulose
-includes organic gels

Inorganic gels

two phase (gel) systems, ex. aluminum hydroxide gel, bentonite magma

Organic gels

single phase gels, condensed matrix is dissolved in liquid media to form homogeneous gelatinous mixture
-when gels contain water, they are called hydrogel. e.g. gelatin, tragacanth, jelly
-when gels contain organic liquid, they are called organogel. ex. petrolatum, mineral oil/polyethyelene gel (plastibase)

Properties of Gels

special properties that facilitate drug absorption & delivery (gels)
•syneresis
•swelling
•imbibition

Syneresis

When a gels stands for some time, it often shrinks because some of the liquid is squeezed out of the system

Swelling

The opposite of syneresis; when a gel takes up some liquid and increases in volume

Imbibition

When a gel takes up a certain amount of liquid with no measurable increase in volume

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