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Basic Concepts in Pharmacology - Coggle Diagram
Basic Concepts
in Pharmacology
Describe the main principles underlying determination of drug dosage regimens
Comprehend and demonstrate understanding with relevant examples the fundamental pharmacokinetic parameters, including HALF-LIFE, VOLUME OF DISTRIBUTION & CLEARANCE, AFTER INTRAVENOUS & ORAL, SINGLE OR MULTIPLE DOSING
Describe, with reference to relevant examples, the body’s various drug handling processes
(Absorption, Distribution, Metabolism and Excretion)
and how these processes may influence the effectiveness of drugs
Pharmacodynamics
what the drug does to the body
relates drug conc to therapeutic response
Pharmacokinetics
what the body does to the drug
relates dosage to conc of drug in plasma
rate at which the amount of drug goes down over unit time
how drugs administered?
speed of onset
(gas/IV if drug required rapidly)
convenience
(orally - requires tablet manufactured so reaches site of target)
ABSORPTION
movement of drug from site of administration
to
site of measurement
STEP 1
process once drug taken orally...
swallow
passes through gut alimentary canal
passes through gut wall (enzymes + lipid bilayer)
sometimes prevents some drugs being absorbed
absorbed into portal system
carried to liver
metabolised in 2 phases
want drug with
HIGH bioavailability
=
low first pass effect
means large proportion of drug makes it through gut and liver + into bloodstream
STEP 2
process once drug reaches systemic circulation...
reaches site of action
may make it to tissue reservoirs (fat + skeletal muscle) - depending on physical chemical properties of drug
if drug water-soluble = filtered by kidney
& eliminated in urine
15-20% cardiac output goes back to liver
& FURTHER METABOLISED
factors affecting amount of drug in systematic circulation after oral dosage
CHEMICAL
properties
chemical stability to acids,
bases & enzymes
solubility in water or lipid
(POLARITY)
molecular weight
(size)
PHYSIOLOGICAL
variables
food, gastric pH
gut motility
cut blood flow
DISTRIBUTION
reversible transfer of absorbed drug into & out of various tissues in body from bloodstream
distribution equilibrium
when drug distribution reaches
highest point
extent & ease with which drug distributes depends on
drugs' physicochemical properties
size
lipid solubility
polarity
distributed widely...
free, unbound
highly lipid soluble
small
non-polar
non-charged
don't distribute well...
large polar molecules get stuck in systemic system
REVERSIBLE
transfer of drug from blood to tissues
drug enters different compartments
once distribution equilibrium reached
drug eliminated @ same rate from all compartments
'Bound Drugs'
Some drugs bind to circulating plasma proteins (acidic + basic drugs)
acidic drugs bind to ALBUMIN
basic drugs bind to α1-acid glycoprotein
plasma binding proteins affected by
age
inflammatory conditions
pathologic stress
COMPETITION
for
plasma binding sites
= clinically important
'Free Drug' = ACTIVE DRUG
METABOLISM
conversion of drug to usually more water soluble compound
EXCRETION
loss of unchanged drug from the body in urine/faeces (includes biliary excretion in liver)
ELIMINATION
what happens to the drug after its been distributed
the eventual loss of drug from body by METABOLISM + EXCRETION
DISPOSITION
what happens after the drug has been absorbed
refers to DISTRIBUTION + ELIMINATION processes that occur after drug absorbed
Discuss how the pharmacokinetic processes and parameters impact drug administration