Pharmacology Flashcards
Define pharmocokinetics
What the body does to the drug
Define pharmoacodynamics
What the drug does to the body
What are different methods of drug transfer across membranes
Aqueous diffusion Passive lipid diffusion Facilitated diffusion Pinocytosis (budding of membrane to ingest into cell) Active transport
What factors affect rate of membrane transport according to ficks law?
Diffusion coefficient Surface area Membrane thickness Partition coefficient (how drug distributes in liquid vs oil) Concentration gradient
What are the methods of drug disposition?
Absorption
Distribution
Metabolism
Excretion
Define bioavailability
Fraction of dose reaching systemic circulation after administration compared to same dose given intravenously
What factors affect drug absorption?
Route of administration
Formulation
How does ionisation affect absorption of drugs?
Drugs are weak acids or bases, with ionisation affected by their pKa and surrounding pH
pH changes with infection etc
Non-ionised drugs- cross by passive diffusion
Ionised drugs- cross by transport mechanisms, facilitated diffusion or pinocytosis
List routes of drug administration and how it affects drug absorbtion
Intravenous- rapid absorption as directly into systemic circulation
Intramuscular- speed dependent on local blood flow and diffusion of muscle
Subcutaneous- slower and less predictable, depends on site, temperature, hydration etc.
Oral- mainly absorbed in small intestine, effected by GI motility, splanchnic blood flow, drug size etc., will undergo first pass metabolism
Inhalational- causes local effect or absorbed into circulation
Epidural, transmucosal, transepithelial- effects at site of admin, can be taken up systemically
What is meant by first pass metabolism?
Concentration of drug given orally is reduced before entering systemic circulation
What determines volume of drug distribution?
Amount administered and concentration of the drug in plasma
How does protein and tissue binding of a drug affect its distribution?
Albumin binds weak acids
Alpha-1-acid glycoprotein binds weak bases
Only unbound drugs can interact and cause effect on the body
(Tissue binding can be specific or non-specific)
How does organ blood flow, membrane permeability and drug solubility effect drug distribution?
Drugs initially go to tissues with high blood flow
Highly lipid soluble drugs will accumulate in fat
Define clearance
Volume of plasma from which drug is completely removed per unit of time
Define half-life
Time taken for plasma concentration to fall 50% of original level
What factors affect drug metabolism and excretion?
Clearance and half life
Define biotransformation
Alteration of substance within the body
Name the stages of drug metabolism
Biotransformation
Excretion
Why do most drugs need to undergo biotransformation before they can be excreted by the kidneys?
Lipophilic and highly bound
Kidneys excrete polar water soluble compounds most easily
What is the main organ of metabolism and how does it work?
Liver
Phase one- convert drug to polar metabolites allowing renal excretion
Phase two- conjugation/combining with substrates
What can be the effects when drugs are activated by metabolism?
Become active drug
Produces active metabolites causing further effects
Produces toxic metabolites
What is the most common excretion of drugs and how does it work?
Renal
Active- tubular secretion
Passive- glomerular filtration
What other methods of drug excretion are there other than renal?
Biliary system
Exhalation
GI system
What is meant by enterohepatic circulation?
Pathway drugs take until plasma concentration drops