14 Kinetics II Flashcards
What are forms of pharmaceutical decomposition?
hydrolysis, oxidation, isomerization, photolysis
what are environmental factors affecting pharmaceutical decomposition?
heat, oxygen, moisture content, light
How can drugs interact with water?
via hydrolysis, where drugs deteriorate due to catalysis or uncatalytic reactions.
catalytic: by hydroxyl or H ions and by alteration of buffer species.
uncatalytic: decomposition with water
How does moisture effect drugs?
Often introduced through excipients. Its effect on stability is dependent on how strongly bound excipients are, or whether or not the drug will come in contact with the moisture.
Moisture also facilitates microbial growth which can further decompose the drug.
How is hydrolysis prevented?
- buffering to prevent pH based hydrolysis
- adding dessicants
- protecting by formulation (micelles, encapsulation etc)
- modifying solubility.
What is oxidation?
The removal of an electropositive atom, radical or electron, or the addition of electronegative atom or radical.
what factors affect autooxidation?
- degree of unsaturation
- presence of fatty acids
- dilution
- temperature
- physical states of compounds.
How can oxidation be prevented?
- exclusion of oxygen contact with product (e.g. air tight packaging)
- inclusion of antioxidants
- inclusion of reducing agents
- dilution of an inert solvent
What is isomerization?
conversion of an active drug into a less active isomer, having the same structural formula but different stereochemical configuration.
what is autooxidation
reactions with atmospheric oxygen causing compounds to go through a free radical phase.
- Highly unstable and reactive, catalysing oxidative degradation.
What is racemization?
Conversion of chiral molecules between L and D forms.
This generally follows first order kinetics and is dependent on temperature, solvent, catalysts and light.
Describe L and D racemers
L rotates the plane of polarised light to the left, and is more pharmalogically active.
D rotates the plane of polarised light to the right and is more stablet.
What is epimerization?
Occurs when compounds have more than one asymmetric carbon atom, creating non-superimposable, non-mirror images or one another
What is photolysis?
The reaction of molecules where Ea is provided by light energy. This is independent from concentration and generally follows zero order kinetics.
