Pharmacokinetics biopharmaceuticals Flashcards
What is biopharmaceutics?
- Study of how physicochemical properties of APIs dosage forms and routes of administration effect rate and extent of API action
Define pharmacodynamics and pharmacokinetics
- Pharmacodynamics: Effect of API on the body
- Pharmacokinetics: Effect of the body on the API
What does ADME stand for
- Absorbtion
- Distribution
- Metabolism
- Excretion
- ADME processes determine resultant API concentrations in the body
ADME rates lead to what plot?
- Cp against time
Absorption from the GIT
- Only API in solution is absorbed
- Only absorbed API acts, if not absorbed will be excreted in faeces
- Suspensions avoid the disintegration stage; small particles of API in suspension can begin dissolving straight away
Why dont all APIs dissolve in water
- add freely soluble definitions
Define dissolution rate and solubility
- Solubility describes the total amount of drug that can dissolve in a finite volume of solvent
- Dissolution rate is how fast the drug dissolves
The rate at which an API dissolves to pass into
solution varies with many factors, including:
- Physical form of API e.g. polymorph
- Particle size of the API
- Stirring
What is the ‘F’ of iV injectables
- F is bioavailability, as a fraction or percentage
- For IV njectables its 1 or 100%
Bioavailability formula
Typical Cp profile for
single GIT dose
- Plot this graph based on blood sample
- Graph is the result of:
- The rate of absorption of the API
- The rate at which the API distributes through the body
- The rate at which the API is eliminated from the body
What is the half life of API
Half-life: time taken for concentration of API in
the plasma to fall to half its value. Effectively a
constant for an “average” patient.
What is lipophicility
- Defined as the affinity of a drug in a lipid environment
- If a drug has high lipopholicity thus means it has high metabolic turnover, low solubility and poor oral absorption
How to calculate LogP
- Log P is the distribution of API between two immiscible liquids
- Participation coefficient (P) measures partitioning of API between fatty and aqueous phase
- octanol is how much of the API will dissolve in a fatty acid phase
- Over how much dissolves in water to caculate liphophicity
Are weak acids and bases lipophilic?
- Majority of drugs are weak acids or bases
- This means they ionise at certain pHs
- The charged/ionised form is more soluble in water
- The charged from will be less soluble in oil - less lipophilic
The stomach as an absorption site
The small intestine features
Diffusion equation
Interpretation of LogP
- Negative LogP prefer aqueous enviroment
- Positive shows preference for fatty membrance
- Best one is around 2
pKa equations
- Extent to which acid dissociates
Interpretation of pKa
- For acid: Higher the pKa the decreasing strength of an acid
- For base: Higher the pKa stronger the base
- Can tell us whether something is a strong acid or base
Each functional group has its own — value?
If an API has more than one ionisable group,
each group has its own pKa value but the
