Mechanism Of Drug Transfer Across Biological Membrane Flashcards
(53 cards)
What is Cmax?
Maximum concentration
What is AUC?
Area under curve
Overall drug exposure
What is Cmin?
Minimum or trough concentrations
May relate with efficacy of HIV drugs
Where should drug concentration be ideally measured?
At the receptor
Define zero order kinetics?
can be defined as the one whose rate is independent of concentration of drug undergoing reaction. That is the rate of reaction cannot be increased by further increase in concentration of reactants.
Zero-order drug absorption from the dosing site into the plasma usually occurs when either …………. or a ………..
the drug is absorbed by a saturable process
zero-order controlled-release delivery system is used
Define first order?
Is a process in which the one whose rate is directly proportional to concentration of the drug undergoing reaction, that is greater the concentration faster the reaction.
First order (kinetic) model as
Define first order?
Is a process in which the one whose rate is directly proportional to concentration of the drug undergoing reaction, that is greater the concentration faster the reaction.
The model of first order kinetics assumes that?
A first order input across the gut wall and first order elimination from the body
About first order (kinetics), this model applies mostly to?
Oral absorption of drugs in solution or rapidly dissolving dosage (immediate release) forms such as tablets, capsules and suppositories
Drug absorption is determined by?
• Physicochemical properties of the drug
• Formulation, for example, tablets, capsules or solutions
• Patients factors –age, sex and disease
• Routes of administration
After oral drug administration, where does majority of the drug absorption occur?
Small intestine
What is the surface area of the intestine and the stomach?
200 square meters
1 square meter respectively
The small intestine, which is more ……….., favours absorption of weakly basic drugs.
basic in pH
The small intestine, which is more basic in pH, favours absorption of ……….?
weakly basic drugs.
Drugs can cross cell membranes by?
• Passive diffusion
• Facilitated passive diffusion
• Active transport
Give examples of passive transport?
Diffusion
Facilitated diffusion
Osmosis. Doesn’t use energy
Examples of active transport?
Protein pumps
Endocytosis
Exocytosis. Cells do use energy
Diffusion rate is directly proportional to the gradient. It also depends on physicochemical m properties of the molecule including?
• Lipophilicity: Lipid-soluble drugs
diffuse most rapidly.
• Size: Small molecules tend to
penetrate membranes more rapidly
than larger ones.
• Degree of ionisation
The ionized form of drugs has low lipid solubility (but high water solubility—ie, hydrophilic) and high
……… and thus cannot penetrate cell membranes easily.
electrical resistance
The proportion of the un-ionized form present (and thus the drug’s ability to cross a membrane) is determined by the …………. and the drug’s ……….
environmental pH
pKa (acid dissociation constant)
What is pKa?
The pKa is the pH at which concentrations of ionized and un-ionized forms are equal.
About passive diffusion efficiency, the efficient molecules include?
Lipids
Hydrocarbons
Anaesthetics
Alcohol
Most drugs
