Drug Actions: Pharmacodynamics and Pharmacokinetics Flashcards
definition of pharmacokinetics
movement of drug particles from GI-tract to body fluids
3 processes of drug absorption
passive (high conc–>low);
active (requires a carrier to move drug across membrane);
pinocytosis- engulfs and carries drug across cell wall (water soluble drugs)
metabolism 1st pass (liver)
- drugs excreted after changed to water form
- nothing happens to drug
- drug metabolized into metabolite (equally or more active than original drug)
Bioavailability
% of drug initially admin that reaches the systemic circulation so it can be used
What is bioavailability affected by?
drug form route of admin GI mucosa and motility food and other drugs changes in liver metabolism caused by liver dysfunction or inadequate hepatic blood flow
pharmacokinetics- distribution
process by which the drug becomes available to the body fluids and tissues
3 factors that influence distribution
- blood flow
- protein binding
- body tissue affinity
protein binding
drug bind to varying degrees with proteins;
free-floating, unbound drugs are the ones with a pharmacologic effect
protein binding %’s; high to low
over 89%- high pb drug
61-89%- mod/ high pb drug
under 30%- low pb drug
Metabolism/ Biotransformation
liver is primary site;
in liver disease- not metabolizing drug well which leads to inc conc of drug and inc risk of toxicity
Half-life (t1/2)
time it takes for one half of the drug conc to be eliminated from the body;
metabolism and elimination affect half life;
short half life- 4-8hrs
long- more than 24hrs
Excretion/ Elimination
primary site- kidneys
urine pH affects excretion
alkaline urine
excretion of weak acid drugs like ASA
sodium bicarbonate
makes urine alkaline; used in ASA overdoses
Pharmacodynamics
study of the way drugs affect the body;
drug concentration and its effect on the body
pharmacodynamics: primary and secondary effect
primary- desirable
secondary- desirable or undesirable
Dose response and maximum efficacy
relationship between the minimum amount vs the maximum amount of a drug needed to produce desired effects/response
onset
time it takes to reach the minimum effective concentration
Receptor Theory
drug binds to receptors on cell membrane;
bind to agonists or antagonists
agonists
receptors that produce a response
antagonists
receptors in which the drugs block response
Nonspecific drug effect
drugs that affect various sites
nonselective drug effect
drug works on various receptors
4 categories of drug action
- stimulation/depression
- replacement (insulin, vitamins, minerals)
- inhibition or killing organisms ( antiinfectives)
- irritation (laxatives)
Therapeutic Index
margin of safety of a drug
low index vs high index
low index has narrow margin of safety;
high index has wide margin of safety
lethal dose/effective dose (closer to 1, greater the toxicity of drug)
trough
rate of elimination of a drug
Loading Dose (LD)
large initial dose when want an immediate drug response; normal doses follow
Side Effects
physiologic effects not related to desired drug effects;
desirable or undesirable
Adverse Reactions
more severe than side effects; unexpected, unintended effects of a drug;
always undesirable
Drug interactions
a different action or effect of a drug as a result of an interaction with one or more other drugs (inside the body)
Drug Incompatibility
a chemical or physical reaction that occurs between two or more drugs within a syringe, iv bag, or iv tubing (outside the body)
Additive drug effect
sum of the effect of 2 drugs; can be desirable or undesirable
codeine and asa combined- greater pain relief (desirable)
bp med and narcotic- dec bp (undesirable)
synergistic drug effect or potentiation
when 1 drug can potentiate the effect of another drug
antagonistic drug effect
when 1 drug will antagonize effects of other drugs
antidotes (vit k and warfarin)
drug-food interactions
can increase or decrease absorption;
dont combine tetracyclines and dairy
