DRUG DISTRIBUTION Flashcards
(27 cards)
What is drug distribution?
Drug distribution refers to the movement of drug to and from the blood and various tissues of the body (for example, fat, muscle, and brain tissue)
and the relative proportions of drug in the tissues.
What is the relationship between drug disposition and the plasma concentration?
Disposition is a process that tend to lower the plasma concentration of drug.
The two major drug disposition process are
1.Distribution
2. Elimination
Factor that affects distribution
1.Blood flow
2. Capillary permeability
3. The degree of binding of the drug to plasma & tissue proteins
4. The relative hydrophobicity of the drug
Physiological factors influencing bioavailability of drugs
- Membrane physiology
- Age
- Pregnancy
- Obesity
- Diet
- Disease status
How much percentage of total body weight does Interstitial fluid represents ?
Interstitial fluid represents about 15% of the total body weight.
How much percentage of total body weight does Intracellular fluid represents ?
Intracellular fluid (fluid inside cells) - 40% of the total body weight.
How much percentage of total body weight does blood plasma represents ?
Blood plasma - 8% of the body weight.
What does the rate of delivery and potential amount of drug distributed into tissues depends on?
vascular permeability, regional blood flow, cardiac output and perfusion rate of the tissue and the ability of the drug to bind tissue and plasma proteins and its lipid solubility
After a drug has entered tissues, drug distribution to the interstitial fluid is determined primarily by
perfusion.
What is interstitial fluid?
The interstitial fluid is the fluid that fills the spaces between cells.
What is perfusion?
Perfusion is the blood flow at the capillary level in tissue.
Four basic processes that explain the disposition of drugs through the body?
absorption, distribution, metabolism, and excretion
What is another name of the volume of distribution?
apparent volume of distribution
What is volume of distribution?
The volume of distribution (Vd) is a pharmacokinetic parameter representing an individual drug’s propensity to either remain in the plasma or redistribute to other tissue compartments.
The equation for Volume of Distribution
Volume of Distribution (L) = Amount of drug in the body (mg) / Plasma concentration of drug (mg/L)
A drug with a high Vd has a propensity (tendency) to ?
To leave the plasma and enter the extravascular compartments of the body, meaning that a higher dose of a drug is required to achieve a given plasma concentration.
A drug with a low Vd has a propensity to?
remain in the plasma meaning a lower dose of a drug is required to achieve a given plasma concentration
A High Vd means
More distribution to other tissue.
A low Vd means
Less distribution to other tissue.
When does a drug become bound to plasma proteins?
Once a drug has been absorbed into the circulation it may become attached (we say bound) to plasma proteins.
What is protein binding like in drug distribution?
However this binding is rapidly reversible and non-specific – that is many drugs may bind to the same protein
What is a free form drug?
This is an unencapsulated drug that is not bound to plasma or tissue proteins.
What is a bound drug?
This is a drug that is inactive and may act as reservoir.
