lec 16 - drugs and pharmacology Flashcards
what is pharmacokinetics
how the body affects a drug
- time course of a drug and its metabolites after administration
what are the 4 main steps of pharmacokinetics
- absorption
- distribution
- metabolism
- excretion / elimination
what are the most common forms of administration
oral, topical, injection
what are the drug factors that affect absorption
formulation (delayed release, aerosol, etc)
solubility (lipid vs water)
particle size
pH
drug ionisation
what are the host factors that affect absorption
motiliy of gut
food in stomach
vomiting / diarrhea
amt of circulatino to the administration site
SA at the administration site
degrees of first pass metabolism
what are the patterns in tissue distribution
blood gets to the brain the fastest out of anywhere in the body
what are the mechanical / biochemical factors involved in distribution
mechanical
- blood flow
- barriers (placenta, blood brain barrier, etc)
biochemical
- lipid solubility
- binding to plasma proteins
- accumulation in tissues
- pH
what is the process of metabolism (biotransformation)
conversion by enzymes to generally more polar (less lipid soluble) forms
- occurs in the smooth ER of cells in the liver (also kidneys, GI, lung, and plasma)
how can drugs be metabolised
activated
changed to another active metabolite
changed to a toxic metabolite
inactivated
what are the phase I and II reactions in drug metabolism
phase I
- conversion to polar metabolite (oxidation, reduction, hydrolysis)
phase II
- coupling of drug (or polar metabolite) with an endogenous substance
what are the factors affecting metabolism
genetics
environment (drug interactions)
physiological (age, disease, nutrition, alcohol, smoking)
what are the main ways of excretion
kidneys (main)
GI tracts
exhalation
saliva
what are the elimination kinetics
half life = time taken for the serum drug level to fall 50% during elimination
1st order kinetics = 5 half lives to reach steady state
what is bioavailability
fraction of the dose that reaches the systemic circulation in an unchanged state
what are the methods of drug transport
passive = diffusion and facilitated diffusion
active = uses ATP to move drug
what are pharmacodynamics
how the drug affects the body (physiological effects)
what are the different types of drug antagonists
chemical
functional - acting independently at different receptors and have opposite physiological effects
competitive - binds to same site
non competitive - binds to different site to change the effect
what are the upper and lower limits of the therapeutic window
lower limit
- concentration that produces half the greatest possible effect
upper limit
- no more than 5-10% of patients experience a harmful side effect
what is the effective vs toxic dose
effective dose = dose that gives the required response in 50% of subjects
toxic dose = dose that produces harmful side effects in 50% of subjects
what is the therapeutic index
toxic dose divided by effective dose
- reflects margin of safety (larger = safety)
what are the effects of tylenol (acetaminophen)
analgesic and antipyretic (anti fever)
what are the pharmacokinetics of acetaminophen
- high absoprtion in SI
- metabolism in liver
- eliminated through urine as metabolites
time to peak = 10-60 mins
half life = 2-3 hours
what are the effects of NSAIDs
anti inflammatory
anti pyretic
anti platelet
analgesic (better than tylenol)
how do NSAIDs act
acts by inhibiting cyclo oxygenase (COX)
