introduction to pharmacology Flashcards
pharmacokinetics
the study of drug movement through the body or “what the body does to the drug”. how does a drug reach the sites of action within the body?
the four pharmacokinetic processes
ADME: administration/absorption, distribution, metabolism, excretion
drug absoprtion
time from administration to entrance into the bloodstream. onset of action is largely determined by rate of absorption, intensity of effect determined by the extent of absorption, bioavailability
bioavailability
the percent of dose that enters blood: IV is 100%, and PO is less than 100%
absorption
extent of movement depends on the ability of drugs to pass to and from the major spaces of the body: intracellular, intravascular, and interstitial. diffusion of a molecule from area of high to low concentration. in many cases, drugs can pass freely between wide junctions, or gaps, in a capillary wall
absorption pt 2
at other times drugs must pass across membranes via: channels or pores, transport systems, or direct membrane penetration (for direct penetration, drug must be lipid soluble, nonpolar, or nonionized
pH partitioning (ion trapping)
stomach acid ph is 2, blood stream pH is 7.38
mechanisms of drug transport
passive diffusion (lipophilic, small size), active transport (electrolytes), carrier proteins (structurally selective, hormones), endocytosis (immune complexes)
drug absorption facts
liquids absorb faster than pills. food in the stomach impairs absorption. most absorption occurs in the duodenum, IM/SC administration results in faster absorption. skin, mucus membranes and lungs serve as additional sites of absorption.
routes of administration: parenteral
the space between the enteric canal and the surface of the body (outside of the GI tract). EX: intravenous (IV), intramuscular (IM), subcutaneous (sub Q)
routes of administration: enteral
using the GI tract
intravenous (IV): barriers to absorption
none
intravenous: patters of absorption
direct
intravenous: advantages
rapid onset, control of level of drug, ability to administer large volumes of fluid
intravenous: disadvantages
expensive, inconvenient, cannot take it back, infection, fluid overload, embolism
intramuscular and subcutaneous: barriers to absorption
none easily passes through spaces of capillary wall
intramuscular and subcutaneous: patterns of absorption
rapid or slow, water solubility of the drug, blood flow to the site of injection
intramuscular and subcutaneous: advantages
good for meds with poor water solubility, used for administration of depot preparations
intramuscular and subcutaneous: disadvantages
discomfort, inconvenient, can be painful, infection, nerve damage
oral (PO): advantages
easy, convenient, safe
oral: barriers to absoprtion
requires patient cooperation, epithelial cells line the GI tract
oral: patterns of absorption are highly variable
solubility/stability of the drug, gastric and intestinal pH, gastric emptying time, presence of food, co-administration of other drugs, coatings on the drugs
additional routes of administration
topical: transdermal, sublingual
inhalation
suppository
direct injection to the site of action
factors affective absorption
route
formulation: dyes, binders, coatings; solubilizers, liposomal preparation
particle size
acid base properties
temperature
blood flow