Kinetics and dynamics Flashcards
what is pharmacokinetics
- how the body handles the drug
- how the drug moves within the body
what are the four processes of pharmacokinetics
- absorption (in the stomach and duodenum)
- distribution
- metabolism
- excretion
what is absorption
- first step in drug transport
- movement of drug from site of administration across one or more body membranes
- drug is transferred from the formulation into the blood
what types of factors can help increase the rate of absorption/distribution
- injection
- liquids (faster than solids)
- gas (faster than liquids)
- smaller
- hotter
- empty stomach (less competition = fast absorption)
- more soluble will make it faster
what is distribution
- process by which drugs are transported after absorption or direct administration into blood
what are some factors that affect distribution
- plasma proteins
- bioavailability
- anatomical barriers; how well the drug passes through these barriers is the one factor that determines its ultimate effectiveness
what is metabolism
- the sum total of all chemical reactions in the body
- drug is transformed by body processes
- biotransformation
what is the primary site of metabolism
- the liver
what is the function of metabolism
- deactivate most drugs
- prodrugs more active after metabolism
- first pass effect via hepatic portal circulation
what is the first pass effect
- drugs given orally are absorbed through the intestinal wall and enter the hepatic portal circulation where they are taken directly to the liver for metabolism before reaching the heart and circulating throughout the rest of the body
what are some factors that affect metabolism
- differing metabolic enzyme function
- age
- kidney disease
- liver disease
- genetics/race
- other medications and foods
what is excretion
- the removal of substances from the body
- via kidneys, respiratory tract, bile or glands
what is the primary organ involved with excretion
- the kidney (removes all unnatural and harmful agents in the blood while maintaining balance of natural substances)
what is the rate of elimination
- amount of drug removed per unit of time
- determines how long the drug remains in the bloodstream
- determines how long the drug will produce its effect
what is half life
- t 1/2
- the length of time for a drug to decrease concentration in the blood by half
- how long the drug will produce its effect
- increased in renal or hepatic diseases
what are some factors that influence the effectiveness of drug therapy
- concentration of drug
- frequency of dosing
- food-drug interactions
- drug-drug interactions
- absorption rate
- metabolic rate
- genetics
- excretion rate
- half-life
- changing medical condition
what are some hepatic diseases that may affect drugs
- cirrhosis: tends to decrease hepatic metabolism of drugs
- acute viral hepatitis: decreases metabolism in about half of drugs
- obstructive jaundice: appears to diminish elimination
how do circulatory diseases affect drugs
- diminished blood flow from a circulatory disorder -> erratic or decreased action in one or more stage of absorption, metabolism, distribution and elimination
how do renal diseases affect drugs
- kidney function decrease -> reduced excretion -> drugs accumulate in the blood -> reduced dosages
how does hypothyroidism affect drugs
- increases the bioavailability of some drugs
- activity of metabolizing enzymes in the liver is reduced
how does hyperthyroidism affect drugs
- decreases bioavailability
- activity of metabolizing enzymes in the liver increased
- increased metabolism of drugs
what is pharmacodynamics
- how the body responds to the drug
- how the drug exerts its effects
- mechanism of action (MOA)
what is the receptor theory
- cellular mechanism by which most drugs produce effects
what is a receptor
- structural component of a cell to which a drug binds in dose related manner in order to produce a response
- lock and key attachment
what is an agonist
- induce response
- specific drug binds to specific receptor to produce response
- give drug a place to bind more easily
what is an antagonist
- inhibits or blocks the response of agonists
- fit receptor but cannot unlock or activate receptor to produce effect (wrong key in the lock)
- occupy the receptor site and block other body chemicals or other drugs from activating the receptor
- NOTE: some drugs = master key to unlock several different types of receptors
what is the dose-response relationship
- as the dose of the drug increases a maximal response or plateau is reached. increasing the drug produces no additional therapeutic response
what is potency
- the drugs strength at certain concentration
what happens as we increase potency (see diagram in slideshow)
- more intense effect than same dose of similar drug
- smaller dose needed to produce same effect as another drug
what is efficacy
- ability of a drug to produce a more intense response as concentration increased
- magnitude of maximal response comparable to another drug
- high efficacy = high response