Final Exam Flashcards - Pharmacokinetics
Onset of Action
-The time it takes a drug to reach the concentration necessary to produce a therapeutic effect
Peak Effect
-The maximum drug effect produced by a drug once the drug has reached maximum concentration in the body
Duration of Action
-The time between onset of action and discontinuation of drug action
4 Phases of Pharmacokinetics
- Absorption
- Distribution
- Metabolism
- Elimination
Pharmacokinetic Phases: Absorption
- Involves movement of drug molecules from the site of administration, across cell membranes, into the circulatory system of the body.
- First phase
- Amount of absorption is influenced by route of administration
- All drugs MUST be in solution before they can be absorbed
Factors That Affect Absorption
- Water solubility
- Fat solubility
- Transport mechanisms in the body
-Movement is restricted unless the drug can pass through the lipid layers of the cell membrane or the drug is small enough to pass through the small aqueous channels
Pharmacokinetic Phases: Distribution
- The process of movement of the drug from the circulatory system, across barrier membranes, to the site of action
- Second Phase
Factors That affect Distribution
The volume of drug that is distributed is influenced by:
- The properties of the drug
- The extent of drug binding to blood proteins or tissue
- The blood supply to the region
- The ability of the drug to cross natural body barriers
Effect of Drug Properties on distribution
- Must be hydrophobic
- Must be lipid soluble
- Nonionized
- Small enough to pass through slit junctions in capillary wall
Pharmacokinetic Phases: Metabolism
-Biochemical process involving transformation of active drugs to a compound that can be easily eliminated OR transformation of prodrugs to active drugs
Prodrug
-Inactive form of drug which must be metabolized to its active form
Biotransformation
- Metabolism of drug to a more active, equally active, or inactive metabolite
- Primary site of biotransformation is the liver
The First Pass Effect
-A process where the liver metabolizes nearly all of a drug to an inactive metabolite, before it passes into general circulation
Factors Influencing Metabolism
- Liver function
- Disease
- Age
- Concurrent administration of drugs
- Genetics
- Nutrition
- Foods
- Gender
Pharmacokinetic Phases: Elimination
- Final phase
- The removal of drug from the body and discontinuation of drug action
Factors Influencing Elimination
- Kidney function
- Disease
- Extent of drug ionization in the urine
- Concurrent administration of drugs
Elimination Half-life (T1/2)
-The time is takes for 50% of the drug to be cleared from the bloodstream
Drug-Receptor Theory
- Drugs interact or bind with targeted cells in the body to produce pharmacologic action
- Drug-receptor binding occurs similar to the action of a lock and key
Affinity
- The attraction that the receptor site has for the drug
- The more similar the drug to the receptor site, the better the affinity
Types of Drug-Receptor Interactions: Agonists
-Binds to and activates the receptor site, eliciting a cellular response
Types of Drug-Receptor Interactions: Inverse Agonist
-Has the affinity, but produces an opposite response
Types of Drug-Receptor Interactions: Partial Agonist
-Binds to and activates a receptor site, but has a weaker cellular response
Therapeutic Index
- The ratio of the effective dose to the lethal dose
- TI=Lethal Dose/Effective Dose
- Narrow TI has very little margin between LD and ED so it can be very dangerous and extreme caution must be taken
Examples of Drugs With Narrow TI
- Warfarin
- Digoxin
- Lithium
Adverse Drug Reactions
- Undesired effects from drug therapy
- Multiple drug therapy is a risk factor
- May be localized or may affect the entire body
Teratogenicity
-ADR’s that produce harm to a developing fetus
Carcinogenicity
-Drugs that stimulate growth of cancers
Hepatotoxicity
-Drugs that are toxic to the liver
Nephrotoxicity
-Drugs that are toxic to kidney
Dependence
-Person must continue to take the drug in order to prevent withdrawal symptoms
Tolerance
-Person must take increasing doses of the drug to produce the same effects as before
