Chapter 4 - Properties of Drugs Flashcards
(43 cards)
What is pharmacokinetics?
study of how drugs pass through the body (absorption in blood stream to elimination)
steps: absorption, distribution, metabolism, elimination
Absorption stage
refers to passage of a drug into the bloodstream; in most cases drug must pass through cell membrane(s); depends of route of administration
ex. intravenous goes to blood directly, orally must pass through mucous membranes in mouth or wall of intestine
Route of administration
affects how much drug reaches blood stream and the speed of absorption (may contribute to abuse)
common routes: inhalation, intramuscular, intravenous, oral
Absorption into body depends on
how well pH of an environment matches the drug’s pKa (acidity of drug)
Henderson-Hasselbalch equation
the closer the pKa and pH, the more non-ionized particles (better diffusion into blood stream)
ex. pKa=3 better absorbed in the stomach (pH=1) than intestine (pH=7)
Liberation (process during absorption)
the process of drug molecules separating form the pill or solution it was dissolved in; many oral drugs are meant to be liberated in small intestines
Distribution stage
after absorption into blood stream, passage of drug from bloodstream into intended body sites
Bioavailability
ability of a drug to reach its intended target
blood-brain barrier
protective layer of cells surrounding blood capillaries in brain that prevent many substances in blood from entering brain; nutrients and some molecules can penetrate it through passive diffusion or active transport
Passive diffusion
fat soluble, neutrally charged, and small in size chemicals can diffuse across the blood brain barrier
Active Transport
consists of membrane channels or transporters that facilitate passage of chemicals through cell membranes
ex. glucose transporter, large amino-acid transporter
Non-specific binding
drugs can sometimes bind to other unintended targets which reduces amount delivered to intended targets
Protein binding
drug may bind to proteins in blood stream (not free to cross blood-brain barrier)
Depot binding
drug may bind to other tissues which reduces amount in blood available to intended target (ex. TCH in fatty tissues)
Metabolizing stage (biotransformation)
process of converting a drug into one or more metabolites
metabolites
products resulting from transformation of a drug via enzymes
mostly smaller molecules; water soluble; may be active or inactive
Individual differences
rapid metabolizers: more metabolic enzymes; decreased amount of drug (have to use high dose or use different class of drugs)
poor metabolizers: fewer metabolic enzymes; prolongs drug life-span
Personalized medicine
prescribe treatments based on patient’s unique biological make up
Elimination stage
process by which drug leaves the body; final stage of pharmacokinetics; several channels, depends on drug (urine/sweat/breath/feces)
Elimination rate
amount of drug eliminated from the body over time
Half life
amount of time required to eliminate half the amount of drug; amount eliminated per unit of time varies; can vary considerably; determines dosing frequency; used if drugs follow first-order kinetics
Zero-order kinetics
drug is eliminated at a fixed amount per unit time (ex. alcohol is eliminated at about 10-14mg per hour)
Pharmacodynamics
mechanisms of action for drug which accounts for its (psychological) effects; some alter neurotransmission directly; some may interfere with neurotransmitter storage/reuptake mechanisms/metabolic enzymes
Binding affinity
The drug’s strength of binding to a receptor; some drugs have a stronger binding to a receptor than a neurotransmitter
