PS400 exam 4 Flashcards
how does mass transfer occur?
via diffusion or convection
dispersion (diffusion + convection)
what is convection and diffusion?
diffusion : Brownian motion & movement towards equilibrium
convection: mass flow of liquid
what is mass transfer important for?
dissolution
crystallization
membrane transport
movement within dosage forms
pharmacokinetics
what is the equation for mass transfer?
t= L^2/ 6D
t- time
L distance
D-diffusion coeff
what does diffusion time depend on?
viscosity of solvent
what t do gasses and solids have?
gasses have lower t
solids have higher t
how does viscosity influence the diffusion coefficient and diffusion time?
increased viscosity–>
decreased diffusion coefficient–> increased diffusion time
what is flux? recognize equation
net rate of a drug movement in a specific direction per area?
j= 1/A dm/dt (dissolution rate)
in flux, what is the relationship between j and A?
what is the relationship between j & dm/dt and A & dm/dt ?
j and A are inversely proportional
j and dm/dt–> directly
A and dm/dt–> directly
what is ficks 2nd law of diffusion under steady state conditions?
C= mx +b
j= constant
what is ficks 1 law of diffusion equation?
j= -D dC/dx ( change in concentration)
j and dc/dx have opposite signs
for ficks 2nd law of diffusion, concentration is linear with position until? what is it independent of?
untill the outside concentration is reached
independent of time
what is drug concentration at tablet surface equal to at steady state?
drug solubility in the dissolution medium
what is drug concentration at L equal to?
drug concentration in bulk solution , which is equal to 0 for sink conditions
what is the noyes Whitney equation for dissolution rate?
dm/dt=DA (Cs-CL/L)
how does particle size affect dissolution rate?
decrease size–> increase A
so increase dm/dt
how does mixing of dissolution medium affect dissolution rate?
increasing in mixing–> decreases L
increases dm/dt
how does viscosity of dissolution medium affect dissolution rate?
decrease viscosity –> increase D
increase dm/dt
how does increasing volume of dissolution medium affect dissolution rate?
increase V–> decrease Cl
increase dm/dt
what is chemical kinetics and how do we apply it to pharmacy?
study of rate of chemical reactions
helps optimize stability & predicting shelf life based on degradation rate
what are zero order kinetic equations?
rate law: A0- At=kt
and t1/2=A/2ko
what are first order kinetic equations?
ln At/ A0= -kt and t1/2=0.693/k1
what order do suspensions follow?
zero order
concentration of a solution remains constance because….
solid can go into solution to replace reacted drug
what are elementary reactions?
have single transition/ activation state
what are bimolecular reactions?
2 molecules reacting, most common
what is transition theory used for?
to determine the energy required for reactants to reach the transition state
what are the assumptions of transition state theory?
fast equilibrium between reactants and transitions state species
reaction rate is proportional to the concentration of the transition state species
what is ionic strength?
measure of concentrations of ions in a solution
more ions—> higher ionic strength
whether the rate constant of increases or decreases depends on the product of charges….. what happens when:
++ or –
+ 0 or - 0
-+ or +-
increase ionic strength and K
increase ionic stength reversible with K
increase ionic strength and decrease K
what happens when ionic strength is low and high?
low: ions have large ionic atmospheres
high: ions in solution shield the ions or interest and the ion atmosphere reduces in size
effect of ionic strength on reaction rate at high ionic strength?
like charges don’t repeal easily–> favoring products
(small ions atmosphere ar shield from seeing each other)
opposing charges attract each other less, favoring reactants
effect of ionic strength of reaction rate at low ionic strength?
like charges more easily repel each other, favoring reactants
(large ion atmosphere see each other at greater distance)
opposing charges more essaying attract each other, favoring products
what is dielectric constant?
measure of attraction/ repulsion between ions in a solution
what happens to dielectric constant (e) when:
++ or –
+/- 0
-+
increase e and k or decrease when adding alcohol
no k effect, decrease e
increase e and dec k
or decrease e and inc k (add alcohol)
what is the Arrhenius equation?
lnk=ln A- Ea/RT
for a 10c reduction in temp, what happens at Ea=10k, 20k and 30k?
shelf life increases by:
2x, 3x, 6x
for 20c reduction in temperature, shelf life increases at Ea=10k, 20k, 30k by:
4x, 9x, 36x
what is accelerated stability studies?
determine shelf life done by measure stability at higher temps and predicting stability at storage temp thru extrapolation
for accelerated stability studies, what do we measure at each temperature?
rate constant over a range of buffer concentrations, extrapolate to determine rate with no buffer
what is step 1 and 2 of accelerated stability studies?
determine bufferless k at several temps at specified ph
plot ln kobs vs 1/T and extrapolate to desired shelf life temp to obtain K extrap
Ph profile, what happens at low, high and int ph?
low: H catalyzes reaction (acid catalysis)
high: OH catalyzes
intermediate: buffering species catalyze reaction
what is passive targeting?
the natural physiological and anatomical characteristics of the body to accumulate drugs in specific areas, particularly in tumors or inflamed tissue
relays on EPR effect
what is active targeting?
uses specific molecular interactions to direct drugs to particular cells or tissues
examples is HER2 targets
Doxil manufacturing?
lipids dissolve in ethanol
mix with aq solution
MLV formation
high pressure extrusion
SUV. formation
DOX loading
purification/ sterilize
Doxil
what is liposome manufacturinhg?
mix w aq solution
MLV format
high pressure exterustoin
