Pharmacokinetics Flashcards
Define Pharmacokinetics
It is what the body does to the drug
Define Absorption
The movement of a drug from its site of administration into the central compartment
Define Distribution
The movement of a drug from the systemic circulation into tissues and body fluids
Define Metabolism
The transformation of a drug into a usable form
Define Elimination
The excretion of a drug from the body
Name the 4 Enteral routes of administration
- Oral (PO)
- Rectal (PR)
- Sublingual (SL) (under the tongue)
- Buccal (between the gums/inner lining of the mouth)
Name the 8 Parenteral routes of administration
- Intravenous (IV)
- Intramuscular (IM)
- Subcutaneous (SC)
- Intrathecal
- Intraarterial
- Topical
- Transdermal
- Respiratory/Pulmonary
What are the 8 factors that affect absorption?
- Dosage form
- Size
- pH
- Blood flow to site
- GI motility/contact time
- Water solubility
- Gut transporters
- Other drugs
What is the First-pass Effect?
The metabolism of a drug before it reaches the systemic circulation
What does the First-pass Effect change about the drug?
Decreases the amount of bioavailable drug
What does the First-pass effect apply to, and how is it measured?
- Applies to oral and rectal administration
- Measured by Extraction Ration (ER)
Define Bioavailability
It’s the fraction of unchanged drug that reaches the systemic circulation, after it is administered.
*IV administration is 100% bioavailable
What are the 4 factors that affect drug Distribution?
- Membrane permeability
- Tissue perfusion
- Protein binding
- Volume of Distribution
What are the 3 scenarios of membrane permeability?
- Drug is confined to circulation (very large drug molecules)
- Drug excluded by cell membranes (very polar drug molecules)
- Drug enriched in fat (lipophilic drugs)
What is Tissue Perfusion?
The rate of blood flow through tissues
*Certain diseases states (liver, heart, and renal failure) change cardiac output therefore changing perfusion of blood through tissues
What is important about protein binding?
Drugs bound to proteins cannot diffuse out of the plasma, they need to be free and unbound
What is important about metabolism?
Drugs require biotransformation to be active
(Phase 1 and 2 rxns)
What is Volume of Distribution?
An indicator of the extent of drug distribution into body fluids and tissues
*only extent and not location
VD= Dose/Concentration in Plasma
Name 5 organs involved in drug metabolism
- Liver
- Gut
- Lungs
- Kidneys
5 Brain
Name 5 factors that affect Metabolism
- Disease States
- Age
- Biological Sex
- Organ function
- Genetic polymorphisms
- Other drugs
What are the main organs involved in Elimination and how is it measured?
- Liver and Kidney
- Measured by Half-life
Describe what Half-life is
Time required to change the amount of a drug in the body by one-half during elimination
Is half-life constant or inconsistent for drugs that follow first-order kinetics?
Constant
Define steady state
When the amount of drug administered per unit time equals the drug eliminated per unit time
How many half-lives are required for steady state?
After approximately four half-lives
What causes fluctuations in half-life?
- Proportional to dose interval/half-time
- Slow absorption
Define clearance
Measure of the ability of the body to eliminate a drug
*Clearance=Rate of elimination/plasma concentration
Describe first-order elimination
- Elimination is directly proportional to concentration
- Constant proportion or rate of drug is eliminated
- Most drugs exhibit this type of elimination
Describe zero-order elimination
- Constant amount of drug is eliminated independent of concentration
- Examples: EtOH, ASA, phenytoin
- Also known as saturable metabolism
- If dosing rate exceeds elimination, steady state cannot be achieved
Name 5 factors that affect elimination
- Disease states
- Biological sex
- Organ function
- Age
- Other drugs
