Pharmacokinetics & Pharmacodynamics Flashcards
Pharmacokinetics
The study of the time course of a drugs journey through the body
Absorption, distribution, metabolism, elimination
what the body does to the drug
Phamacodynamics
The study of the existing biological effects resulting from the interaction between drugs and biological systems
what the drug does to the body
Active drug
Free drug
Drug that is not bound to protein
Peds most reliable route of med admin
IV
Peds most desirable route of med admin
Enteral
Topical med admin in peds
Reduces as skin matures
absorption
transfer of drug from the site of administration into circulation
bioavailability
amount of drug absorbed into circualtion
distribution
partitioning of drug from the circulation into various body fluids, organs, and tissues
metabolism
biotransformation of the drug
elimination
elimination of the drug from the body
primary site of metabolism
the liver
primary site of elimination
kidneys
potency
amount of drug required to cause effect
efficacy
response of the drug (even less efficacious drugs may not have full efficacy)
phase I reactions
simple reactions
CYP450
oxidation, reduction, hydrolysis
phase II reactions
more complex reactions with molecules added together
conjugation, glucuronidation, sulfation, acetylation, methylation
clearance
rate at which drug is eliminated
factors that affect GFR
protein binding
renal blood flow
area and nature of glomerular membrane
methods of elimination
glomerular filtration, tubular secretion, tubular reabsorption
single compartment kinetics
drug is delivered to the central compartment, then eliminated and has action
multicompartment kinetics
drug is delivered to central compartment, and rapidly distributed to the peripheral compartment
alpha phase
distribution phase of multicompartment kinetics
drug is still being eliminated - blood levels are high
DO NOT DRAW LEVELS DURING THIS PHASE
beta phase
phase of gradual elimination - like single compartment kinetics
volume of distribution
size of compartment in which drug distributes
Vd=dose/concentration
half life
time for the drug concentration to decrease by one half
generally takes 5 half-lives to eliminate drug from the body
first order kinetics
linear or exponential clearance - constant fraction or proportion of drug is removed per unit of time
ideal for drug calculations!
zero order kinetics
mechanisms for elimination become saturated - more drug is present than system can process, so drug is NOT eliminated at a constant (linear) rate
a small increase in dose will result in a large increase in the plasma concentration
clearance
rate of elimination / drug concentration
single most important factor in determining drug concentrations
depends on: dose, organ blood flow, intrinsic function of the liver or kidneys
is it ok to draw peaks/troughs off schedule?
okay to get peaks late and troughs early
do not obtain peaks early!!!
do not get troughs late!!!
how to titrate meds based on peaks and troughs?
peaks - adjust dose
troughs - adjust interval
sensitivity
concentration required to produce 50% of maximum effect
type I reaction
anaphylactic
type II reaction
cytolytic
ex. hemolytic anemia, ABO mismatch
type III reaction
arthrus
ex. serum sickness, RA, SLE, cephalosporin rxn
type IV reaction
delayed hypersensitivity reaction
ex. contact dermatitis
adverse drug event
any untoward medical occurance that may present during treatment with a pharmaceutical product but which does not necessarily have a causal relationship with this treatment
ex. falls
medication error
any PREVENTABLE event that may cause or lead to inappropriate medication use or patient harm while the medication is in the control of the healthcare professional, patient, or consumer
tool used to determine risk of drug interactions for hepatic failure
childs-pugh classification
considers bilirubin, albumin, ascites, encephalopathy, prothrombin time
important meds to evaluate for in hepatic failure
drugs that depend on hepatic metabolism for clearance
high hepatic extraction ration
degree of protein binding
free drugs have greater effect to target sites
benzos, fluoroquinolones, H2 antagonists, loop diuretics
renal failure changes
changes in protein binding
altered volume of distribution d/t fluid overload or altered tissue binding
decreased clearance
cockcroft-galt equation
estimates CrCl
CrCl = (140-age)(ABW in kg)/72(Scr)
females - CrCl * 0.85
Normal = >90 ml/min ABW = actual body weight
important meds to monitor in renal failure
drugs that may worsen renal function
are renally eliminated
are metabolized to active/renally eliminated metabolites
are highly protein bound
CHF changes
decreased blood flow to GI and muscles - decreased absorption
decreased interstitial fluid, decreased Vd, decreased hepatic blood flow, decreased clearance
drug interactions
occurs when the effects of one drug are altered by the co-administration of another substance
phase of pharmacokinetics that causes the most adverse drug reactions
metabolism
common inducers of drug metabolism
carbamazepine
phenobarbital
phenytoin
rifampin
common inhibitors of drug metabolism
omeprazole
trimethoprim
metronizadole
creatinine clearance for peds
K * L/SCr
L = length in cm K = constant SCr= serum creatinine in mg/dL
do peds require larger or smaller doses than adults?
larger per kg
average CrCl for elderly patients
50-80 ml/min
creatinine clearance =
(140-age)(ABW) /72(Scr)
factors that make meds easy to pass into breast milk
small size
weak base
low binding
lipid soluble
