p'kinetics and p'dynamics Flashcards
What is pharmacokinetics?
study of drug movement thru the body
4 process of pharmacokinetics?
- absorption
- distribution
- metabolism
- excretion
3 ways for drugs to cross cell membrane? Which is most common?
- channels/pores (small)
- transport system (requires energy)
- direct penetration (move thru cell membrane itself)
- most common
What makes a drug or molecule most likely to pass thru cell membrane?
a drug needs to LIPID SOLUBE to pass thru lipid bilayer
What are 2 other factors that effect a molecules ability to enter a cell? (think basic chemistry)
- polarity (like dissolves like) – polar molecules cant pass tru bilayer
- ions cannot pass thru
Movement of a drug from site of administration into the blood….
Absorption
What are factors that can effect absorption?
- rate of dissolution (pill vs liquid)
- increase rate of absorption: if increase surface area, blood flow, lipid solubility
- ph partitioning (acidic accumulate on alkaline side and vice versa)
- route of administration
What is the difference b/w parental and enteral administration?
PARENTAL = absorbed direct into bld stream (IV,IM,SubCu,Intra-arterial) ENTERAL= absorbed/taken in by GI tract
What are 2 types of coatings/formats for enteral medication?
- Enteric = won’t dissolve in stomach = dissolves in intestine
- Sustained release= released steadily thru out the day
Which administration is fastest and which is slowest?
fast = IV (30-60 sec) slow= ingestion (30-90 minutes)
Drug movement from the blood to the interstitial space and cells…
Distribution
Factors that affect distribution
- blood flow to tissues
- ability of drug to exit the vascular system (Blood brain barrier, placenta, protein binding)
- ability of drugs to enter cells
Enzymatic alteration of a drug….
Metabolism
Where does drug metabolism primarily occur?
LIVER
What is the hepatic enzyme system that changes drugs and is 12 closely related enzyme families?
Cytochrome P450 system
What changes does metabolism cause to a drug?
- accelerate excretion
- in/activation
- toxicity
- increase metabolism (inducers)
- decrease metabolism (inhibitors)
What is the First Pass Effect?
=rapid hepatic inactivation of certain ORAL drugs
oral drug > GI absorption > hepatic portal vein takes to live > liver metabolizes drug >blood stream circulation
Where do all oral medications (except sublingual) go before systemic circulation?
LIVER
What are some results of the First pass effect?
- inactivates portion fo drug
- decrease therapeutic effect > give higher dose
- delayed time to take effect
Removal of drugs from the body…
Excretion
What organ usually takes care of drug excretion? what are some other methods for excretion?
KIDNEY
other: bile, lungs, milk, sweat, saliva, skin, hair, tears, liver
3 ways kidney effects excretion
- GFR (if attached to albumin = cant fit in glomerulus for filtration)
- Passive Tubular Reabsorption (lipid soluble drugs passively move into blood from tubule)
- Active Tubular Secretion (pump drugs from blood into tubular urine)
What do we look at to see if a drug worked?
Plasma Drug Levels
What is a single dose time course?
what happens with one dose of drug
When are drug levels highest?
during absorption and distribution
When are drug levels lowest?
metabolism and excretion
What is a drug 1/2 life?
time it takes for amount of drug in body to decrease by 50%
Why do I care about Drug 1/2 life (3 reasons)
- duration of action after single dose
- time required to reach steady state
- dosing frequency
How many half lives does it take to reach plateau?
4 (as long as dosage remains constant)
What is a loading dose?
increase initial dose of drug to achieve plateau more quickly
How many half lives does it take for most of drug to be eliminated from body?
4
What is the difference between Peak and Trough?
PEAK= greatest concentration of drug in BLOOD
-30 min AFTER infusion
TROUGH= greatest concentration of drug in TISSUE
-30 min PRIOR to next infusion
What is pharmacodynamics?
study of DRUGS effect on BODY
-aka what drugs due to the body and how they do it
3 Dose response relationships?
- increase dose > response progressively increase
- EFFICACY
- POTENCY
What is the difference between Efficacy and Potency?
EFFICACY= largest effect a drug can produce (limits of tylenol to treat pain)
POTENCY= dosage needed to produce effect (#of MG)
Morphine (2 mg) vs Dilaudid (.3MG) have same EFFICACY but
Dilaudid is more potent because it needs less mg to produce same effect
What makes the specificity of a drug possible?
Receptors
What happens in you increase a drugs selectivity?
decrease side effects
** selectivity does NOT equal safety
What do drugs that bind to receptors do?
Mimic or block body’s natural function
Receptors work as a ___ and ____ mechanism
lock and key
A drugs strength of attraction to a receptor is …..
affinity
A drugs ability to activate a receptor upon binding is….
intrinsic activity
This kind of drug activates receptors and MIMICS the body’s response
Agonist
This kind of drug blocks action by binding to receptors
Antagonist
Do Agonists have affinity or intrinsic activity?
BOTH
Do Antagonists have affinity or intrinsic activity?
Affinity but no intrinsic activity
How do agonist and antagonists effect processes?
Agonist = slower or faster process Antagonist = no observable effect unless agonist present
What is a partial agonist?
- acts like agonist and antagonist
- cannot produce full effect of agonist (detox drug for heroin makes feel sick but also help with detox)
What is the difference between competitive and noncompetitive antagonists?
Competitive = binds REVERSIBLY (surmountable)
Non competitive = binds IRREVERSIBLY (insurmountable)
-reduces # of binding spots for agonist
What is Average Effective Dose?
ED50
-dose required to produce a therapeutic effect in 50% of ppl
What is a Lethal Dose?
LD50
-dose that is lethal to 50% of animals treated
What is the relationship between therapeutic index, and drug safety as it pertains to lethal dose?
^ therapeutic index = ^ safety of drug
—> more space b/w safe and lethal dose
