Pharmacology Class 2020 Pharmacokinetics Flashcards
Pharmacokinetics
What does the body do to the drug.Concerns the relationship of the drug with the absorption, distribution, metabolism, elimination processes to the intensity and time course of pharmacologic effects of drugs and chemicals.
What variables affect pharmacokinetics?
Age
Organ Function
Health
Absorption
is the movement of a drug from its site of administration into the central compartment which is the blood stream.
Bioavalability
F is the fraction of unchanged drug reaching systemic circulation following administration by any route.
Which route of administration provides 100% bioavalability?
IV
How does pH affect drug passing through barriers?
Change in pH affects ionization to pass through.
A more acidic drug will accumulate on the more basic side of membrane and a more basic drug will accumulate on more acidic side of the membrane.
Which drugs pass through rapidly through diffusion?
Lipid soluble
Henderson Hasselbach
Depending on pKa of drug
What is the main way of transport of drugs?
Passive Diffusion which is where a drug molecule penetrates by diffusion along a concentration gradient
What is active transport?
Requires energy to move a drug against an electrochemical gradient.
Example: sodium potsssium ATPase
Concentration
Rate of diffusion away from the site of administration is directly proportional to the concentration
Which part of gut has most absorption capacity?
Small intestine due to Surface Area is large compared to the small surface area of the stomach.
The factor that affect the release of the drug from stomach to small intestine can affect what?
Absorption can be affected by delayed gastric emptying
What can influence late gastric emptying?
High fats and High carbs
Intense Exercise
Cold beverages
What accelerates gastric emptying?
Moderate Exercise
Hot beverages
Recumbent position
How does slow gastric emptying affect aspirin?
More stomach irritation
How does slow gastric emptying affect penicillin?
It is sensitive to pH and it is less efficient.
Tissues that are highly vascular have more extensive absorption.
True or False
True
Inflammation increases absorption
True
Edematous areas increase absorption
False.
Decrease
There is less vascularity around gluteus muscle so why would the rate of absorption be affected?
Fat is not highly vascular like muscle
What drug is most difficult to pass through the plasma membrane?
Ionized and hydrophilic
What drug type passes through the blood brain barrier, placenta, fat and skin?
Lipophilic drugs
Ficks Law of Diffusion
The rate of diffusion is proportional to thickness of the area you are dealing with. The thicker the area the slower the rate and the larger the area the greater the area of absorption will be.
Distribution
The partitioning of a drug between the blood and extravascular tissue. How well it distributes determines how well it works
Where is the drug contained the most initially in distribution?
Most perfuse organ such as
Brain
Kidney
How does the size of the organ affect distribution of the drug?
Determines the concentration gradient between the blood and the organ.
The larger it is the higher the capacity of distribution into the organ.
Example:
Skeletal muscle has higher capacity than the brain because brain is smaller.
Where is albumin found?
A lot of drugs will bind to albumin within the blood
What is solubility?
Organs with high lipid content will dissolve a high concentration of lipid soluble agents rapidly.
Volume of Distribution
Relates to the amount of drug in the body to the concentration of drug in the blood
What is Vd?
Apparent Volume of Distribution which comes from the blood divided by the concentration
1000mg drug A
Sample of blood 100mg/L
Vd= 10L
Two Compartment Model
A two compartment model considers the movement of drugs between the central compartment and the peripheral compartment
Once injected the highly perfused areas get the drug first and then the distribution phase happens where the central compartment equilibrates with the peripheral compartment.
Distribution Phase
Plasma concentration is highest immediately after the IV bolus but then rapidly decreases as the drug distributes into the peripheral compartment.
Elimination Phase
After a distribution reaches equilibrium and the plasma concentration decreases at a constant rate
Drug introduced into central compartment and equilibrates with peripheral compartment causing a decline on the graph. Where the decline on the graph f line decline slows down is elimination phase.
Elimination paths:
Fecal
Lungs
Thiopental
General Anesthetic
Shortly after injection, the drug level in the blood is high initially and then it drops and you see an increase in the concentration in other parts of the body such as in the brain where it reaches max concentration.
Redistribution terminates drug action or effect through distribution into other tissues
Protein Binding is important because it inhibits the action of the drug.The level of protein in plasma affects free drug concentration.
True or False
True
What medical condition increases the amount of free drug?
Hypoalbuminemia caused by
Cirrhosis
CHF
Malnutrition
More Free Drug equals more effect
Yes
What is the negative effect of free drug high concentration?
Side effects
Which molecule affect the binding of basic drugs to proteins?
alpha 1 acid glycoprotein
What factors determine the fraction of bound drug?
Drug Concentration
Affinity of Binding Sites
Number of Binding Sites
If a drug does not distribute within the tissue, what can happen?
Accumulation which cause toxicity.
Ototoxicity and Renal Toxicity
What drug can inhibit bone growth?
Tetracycline and heavy metals
Where in the body is a drug’s effect most potent
Blood Stream
What type of drugs do Albumin bind?
Acidic drugs which are most drugs
When a drug binds to a plasma protein like albumin, what happens to its capacity to exert an effect?
It is bound so its effect goes down
Only the free drug exerts a biological effect.
True or False
True
What is Albumin’s main role in the body?
To preserve the oncotic pressure of plasma which is why it stays only in the blood.
