Chemical Kinetics and Stability Flashcards
what must be known to ensure that the patient receives the correct dose of a drug?
rate of degradation
chemicals in nature and take place at definitive rates
degradative reactions
the study of rate of a chemical reaction
chemical kinetics
speed of a chemical reaction
reaction rate
chemical kinetics deals with the ___________ and the mode of action of their degradation through the _______________
stability of drugs, examination of rate of reaction
what can chemical kinetics provide to anticipate stability problems?
predictive information
Reactions occur when reactant molecules
“effectively collide.”
collision theory
facilitate the breaking and forming of bonds and the rearrangement of atoms
effective collision
A + BX -> B + AX
effective collision
factors that affect reaction rates
- concentration effects
- temperature effects
- catalyst effects
*More reactant particles that collide
→the more often a reaction can occur
concentration effects
the reaction rate usually increases as the concentration of the reactants _____
increases
*Increase in temperature
→Increase in KE
→Faster molecules
→More collision
*The reaction rate of virtually all reactions
increases with increasing temperature.
temperature effects
- a substance that increases the reaction rate without undergoing a net chemical change itself
- Lowers Ea
catalysts
formula for reaction rate (law/expression/equation)
= aA + bB -> cC + dD
= 𝑟𝑎𝑡𝑒=𝑘[𝐴]𝑎[𝐵]𝑏
what is the k in 𝑟𝑎𝑡𝑒=𝑘[𝐴]𝑎[𝐵]𝑏 ?
rate constant
what is the A and B in 𝑟𝑎𝑡𝑒=𝑘[𝐴]𝑎[𝐵]𝑏 ?
concentration of reactants
what is the a + b in 𝑟𝑎𝑡𝑒=𝑘[𝐴]𝑎[𝐵]𝑏 ?
order of reaction
equation of the line:
= y = mx + b
= 𝑪=−𝒌𝒕+𝑪𝟎
what is the k in 𝑪=−𝒌𝒕+𝑪𝟎
rate constant
what is the Co in 𝑪=−𝒌𝒕+𝑪𝟎
initial concentration
formula for rate constant (select the last two points)
𝒎= 𝐶2 −𝐶1 / 𝑡2 −𝑡1
the time required for one-half (50%) of the material to disappear
half-life (t 1/2)
formula for half life (zero order)
𝒕𝟏/𝟐 = (𝟎.𝟓)(𝑪𝒐) / 𝒌
the time required for 10% of the material
to disappear
shelf-life (t90)
formula for shelf life (zero order)
𝒕𝟗𝟎 =(𝟎.𝟏)(𝑪𝒐) / 𝒌
A plot of the remaining drug concentration, C versus t, gives a
curved line
However, a plot of natural logarithm of drug concentration, ln C vs t, gives a ________ with a slope equal to -k.
straight line
formula for rate constant (with natural logarithm)
𝒎= (𝑙𝑛𝐶2 −𝑙𝑛𝐶1) / (𝑡2 −𝑡1)
formula for half life (first-order)
t1/2 = 0.693 / k
formula for shelf life (first order)
t90 = 0.105 / k
Application of Chemical Kinetics in Pharmacy
- production of more stable drug preparations, the dosage and rationale of which may be established on sound scientific principles
- assist the physician and patient regarding the proper storage and use of medicinal agents.
the time period during which a drug product is expected to remain within the approved specification for use, provided that it is stored under the conditions defined on the container label.
shelf life
the date placed on the container label of a drug product designating the time prior to which a batch of the product is expected to remain within the approved shelf-life specification
expiration date
determination of shelf-life
- arrhenius equation
- Q10 method
used to predict temperature stability
Arrhenius Equation
can estimate the effect of a 10° rise in temperature on the stability of pharmaceuticals
Q10 Method
evaluation of stability of drug products
- accelerated stability studies
- stress testing
designed to increase the rate of chemical degradation or physical change of a drug or drug product by using exaggerated storage conditions
accelerated stability studies
carried out under more severe conditions than those used for accelerated testing
- High temperature, humidity, high or low pH
stress testing
a chemical bond is split via the addition of water
e.g. esters and amides
Protection:
1. pH buffers
2. Type of solvent
3. Structure
modification
hydrolysis
transfer of electrons
e.g. steroids, vitamins, antibiotics
Protection:
1. Low O2 content
2. Antioxidants
3. pH buffers
4. Type of Solvent
oxidation
absorption of radiant energy in the form of light
e.g. nifedipine, hydrocortisone
Protection:
1. Storage condition
photolysis
