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58 Cards in this Set
- Front
- Back
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water of imbibition
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held in fissures and pores
may promote chem reaction |
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types of dispersed systems
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molecular dispersion-homogenous solution; invisible under EM
colloidal dispersion: slow particle diffusion...polymer sol'ns coarse dispersion: susp, emulsion |
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formulation consideration for orally administered suspensions
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active
wetting agent flocculating agent suspending agent (v enhancing) colorant sweetener acidifier purified water |
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contact angle measurement
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high=insignificant or no wetting
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nonionic surfactants
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pluronics/poloxamers: linear block copolymer
spans: partial esters of fatty acids and hexitol anhydride tweens/polysorbates: derived from spans..more alkyl gps |
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ionic surfactants
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anionic: sodium lauryl sulfate: topical eg soaps
Cationic: Hexadecyltrimethyl ammonium bromide |
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HLB value for surfactants
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hydrophilic-lipophilic balance: how decide which to use
value of 1-9 good for just wetting value of 10-18 can solubilize |
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HLB equation
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Say Sodium Lauryl sulfate has a +38.7 value for hydrophilic group contribution to HLB,
HLB=7+ sum of hydrophilic group # + sum of lipophilic group # =7 + 38.7 + (12*-.475) |
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a flocculating agent is used for controlled flocculation. What is the affect on zeta potential?
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since you are adding a cationic adsorbent and anionic flocculant (or vice versa-either way, are increasing electrolyte concentration), the zeta potential is decreased.
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type of flocculating agent to use
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multivalent is most effective, but compatibility problems arise
combo of ionic or nonionic surfactants used with lipophilic polymers |
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typical flocculating agents
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surfactants-anionic or cationic, polymers (hydrophilic)-anionic or nonionic, Clay-these tend to be anionic, electrolytes...don't really need to memorize
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Suspending or viscosity imparting agents
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Gum, cellulosics, clay...also carbopol, gelatin, PEG, povidone
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viscosity of water
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1cP
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poise
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the shearing force required to produce a velocity of 1 cm/sec between two parallel layers of liquid of 1 cm^2 in area and separated by a distance of 1 cm.
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absolute viscosity
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proportional to shearing stress and inversely proportional to rate of shear
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Plastic flow (Non-newt)
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There is a yield value before it starts to move. Handy in suspension because gravitational force on particle isn't sufficient to cause particle to displace. Useful for storing and filling properties. Not common.
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Pseudoplastic flow (non-newt)
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Takes a while to get to full rate, but starts right away. Good for suspension and pharmaceuticals. More accessible than plastic flowers.
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Dilatant flow (non-newt)
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More force leads to less displacement b/c of mol-mol interactions causing bridging/ridgidity. Not common and bad for lrg manufacturing. Viscosity increases with increasing SHEAR RATE. Deflocculated--majority consisting of dispersed phase. Dilatant behavior is diff based on diff force, NOT time.
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shear dependent, time independent
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pseudoplastic, plastic, dilatant
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shear dependent, time dependent
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thixotropy, negative thixotropy, rheoplexy
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thixotropy (in plastic and pseudoplastic flow systems).
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aka sheer thinning: viscosity decr w/ incr shear and time at a constant sheer
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commonly used preservatives for suspension (none are good at above neutral pH, but above 7 PH kills anyway)
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parabens:
sorbic acid: 4' ammonium salt eg BAK benzyl alcohol benzoic acid |
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parabens
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heat to solubilize. inactivated by high concentration of surfactant, poor sol in water, bad taste, slow kill time, kill mold and yeast
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sorbic acid
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unstable in polyethylene containers
don't use above pH 6 sol in h2o good tast |
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quaternary ammonium salt eg BAK
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potent, but + chrg is prob if have many anionic eg carbopols
dont use w/ anionic surfactants and polymers sol in h2o of course rapid kill opthalmic |
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benzyl alcohol
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restricted use in lrg vol parenterals: systemic toxicity possible
sol in h2o of course inactivated by concentrations of surfactants injectable and topical preservative |
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benzoic acid
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don't use above pH5
sol in h2o of course good taste |
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buffering agents in suspensions for chemical stability
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ammonium solution, strong
citric acid sodium citrate fumaric acid |
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flavors in suspensions
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cherry grape orange peppermint
-mint or fruit for antacid |
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colorants in suspensions
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relate to flavor
may be suspending agent color select whether neutral, +, or - to avoid incompatibility.. |
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physical stability tests that are passive
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aesthetic appeal
pH SG sedimentation rate zeta potential compatibility w/ container compatibility w/ cap-liner microscopic examination crystal size uniform drug determination |
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physical stability tests that are active
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redispersibility
rheological measurements stress tests accelerated shock cycles freeze-thaw cycles |
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causes of pH change
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bad buffer
altered surface chrg from drug, surfactant, or polymers drug decomposition |
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causes of crystal growth
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polymorph between crystalline and amorphous---lower the interfacial tension
extreme diff in crystal size-narrow the PS cooling of an already saturated solution--create protective coat around particles w/ colloids XS surfactant-->solubilized and precipitated. |
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ostwald ripening
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crystal regrowth in wrong crystal form: growth of lrg particles at the expense of smaller ones as a result of a diff in the solubility of the particles of varying sizes.
prevent by adsorbing a polymer on the drug crystal, making a hydration sheath. |
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deflocculation causes
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XS electrolytes
crystal growth--try controlled flocculation |
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poor redispersibility causes
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deflocculation
PS non-uniformity questionable |
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settling problem causes
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not enough suspending agent=low yield stress
electrolyte concentration |
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physical breakdown of suspension causes
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severe flocculation of suspending agent--check electrolyte content
change in suspending agent--replace it |
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cause of flotation agent
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hydrophobic drug isn't adequately wetted by the suspension medium due to air adhering to the wetted or insufficiently un-wetted particles
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causes of caking
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crystal growth and fusion--chng PS, incr density, incr viscosity, check zeta pot
deflocculated system |
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causes of decr drug potency
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susp isn't homogenous, variation in PS, too large PS---check ionic charge of drug and suspending agent, PS and distribution, ionic chrg of flocculating and suspending agent, mix technique and filling method.
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physical props of emulsions
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internal external phase
drop size and size distributions concentration of internal dispersed phase rheology electical properties multiple phase emulsions |
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macro- vs microemulsion
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macro >100nm...thermodynamically unstable
micro is <100 and is stable...many cosolvents and interactions, won't revert to something else, but cosolv toxicity issues |
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appearance of emulsion depends on droplet size
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1+mm is milky
.1-1 is blue-white .05-.1 is gray, semi-transparent <.05 is transparent |
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emulsifying agents
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surface active
hydrophilic colloids finely divided solid particles |
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bancroft's rule
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the phase in which an emulsifier is more soluble/is contained in constitutes the continuous phase
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low HLB purpose of surfactant
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antifoaming
w/o emulsifier |
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intermediate HLB purpose of surfactant
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milky dispersion---wetting agent; emulsifier if dispersion is stable
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high HLB purpose of surfactant
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O/W emulsifier
solubilizing agent in the clear solution |
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triethanolamine oleate
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o/w emulsion (anionic)
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n-cetyl n-ethyl morpholinum ethosulfate
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o/w emulsion (cationic)
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sorbitan monooleate (span 80)
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w/o, nonionic
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tween 80
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nonionic o/w
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acacia
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o/w
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bentonite
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o/w and w/o
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veegum
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o/w
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rate of coalescence of emulsion at top/bottom surface depends on :
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physical nature of the interfacial surfactant film
electrical or steric barrier of o/w viscosity of continuous phase: incr leads to decr collision and so lower coalescence size distribution of droplets: narrow distribution better phase volume ratio: incr V dispersed decreases stability. phase inversion can occur. temperature incr ->stability decr temp affects-interfacial tension, sol of surfactant, brownian motion, viscosity of liq. |
