Pharmacokinetics/dynamics Flashcards
Key terms relating to pharmacokinetics and pharmacodynamics
Pharmacodynamics
What the drug does as it moves throughout the body
Pharmacokinetics
Drug movement through the body and what the body does to the drug
absorption, distribution, metabolism, excretion
First pass effect
absorption by GI tract, moves to liver where some drugs are completely inactivated & excreted, decreasing bioavailability
Bioavailability
how much of a drug is available for use by body after the first pass
oral drugs always <100%, IV = 100%
Protein Binding
drugs that have an affinity for certain proteins bind to them, decreasing amount of free drug that can work in the body
increased binding = decreased free drug –> higher dose required
when two highly bound drugs are administered at the same time, they compete for available protein sites, which can cause an increase in free drug %, but may also lead to drug accumulation and toxicity
Blood-Brain Barrier
95% of drugs cannot cross
must have a carrier protein or be highly lipid soluble to cross
extra line of defense for fetuses, since most drugs can/do cross placental membrane
Prodrug
inactive drug/compound that metabolizes into an active drug once administered, and can be more effective than regular drugs
regular meds don’t need to be converted first before effective
ie. codeine –> morphine in body
Half-life
time it takes for half of the original dose to be present in the body
reason for time period b/w doses, don’t want to OD
ie. Ibu has 2hr 1/2life –> 4-6 hours b/w doses
Primary vs. Secondary Effect
desirable primary effect, (un)desireable secondary effect
ie. benadryl treats allergic rxn (primary), but also causes drowsiness (secondary)
Drug potency
amount of drug needed to elicit specfic physiological response
high potency = lower dose
higher dose needed for those with a tolerance like addicts or redheads
Maximal efficacy
point at which increased doseage does not increase desired therapeutic response
pleateau reached
Therapeutic index
narrow window between a therapeutic dose and a toxic dose
narrow index drugs require close monitoring
Onset
range of time it takes for drug to reach minimum effective concentration
when it starts “taking the edge off”
Peak
highest plasma concentration of drug in blood at a specific time
1hr for IV, ~2-3hrs for pills, ~2-4hrs for IM
- indicates rate of absorption: too low means effective concentration not yet reached
- drawn at expected peak time
ie. INR for blood thinners
Duration
length of time drug exerts a therapeutic effect
longer for IV than pill
Trough level
lowest plasma concentration of drug due to elimination
drawn just before next dose
Agonist
drugs that activate receptors to produce a response
ie. albuterol
Partial agonist
elicit only moderate activity when binding to receptors, but prevent receptor activation by other drugs
like a combination of agonist and antagonist
Antagonist
prevent receptor action and block a response
ie. naloxone
Nonspecific drug
affect multiple receptor sites of same receptor type
effects seen across similar tissues
ie. albuterol
Nonselective drug
affects multiple different receptors
effects seen throughout system
ie. epinephrine
Drug toxicity
occurs when drug levels exceed therapeutic range, producing specific effects
ie. amiodarone –> “little blind smurf that can’t breathe” -eileen
Tachyphlaxis
acute, rapid decrease in response to a drug
very rare
Additive drug effects
sum effect of two drugs that produce a proportionately greater effect
2 + 2 = 4
Synergystic drug effects and potentiation
effect of drugs is much greater than the effects of either alone, or their proportionate sum
2 + 2 = 10
ie. nebulizer
Antagonistic drug effects
one drug reduces or blocks the effect of the other
can be considered a drug interaction
