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how drugs interact with receptors. drugs go through the whole body, but
only receptors, when targeted, do the action.
pharmacodynamics
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2 examples of zero-order reactions
constant amount of drug is metabolized per unit time. nothing to do with concentration. the graph drops down in a straight line, no half life or curve.
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what a drug is called when it goes in the body in an inactive form, changes (biotransforms) within the body and THEN becomes the active drug
prodrug
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first-order kinetics: concentration dependent
constant FRACTION of drug metabolized per unit time (curve, half-lives)
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explain what it means to have a half life of one hour
half the drug is metabolized in one hour. after another hour, half of what was left is metabolized. etc. larger volume distribution (Vd) takes longer to be broken down.
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pharmacokinetics: where the drug goes in your body
- distribution
- "the process by which a drug reversibly leaves the bloodstream and enters the extracellular fluid and/or cells"
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3 factors that affect distribution (pharmacokinetics)
- blood flow
- capillary (blood brain barrier)
- binding of drugs to proteins (albumin)
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pharmacokinetics: how a drug is converted in your body
metabolism
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2 drugs are therapeutically equivalent if
they have comparable efficacy and safety (same effect)
-
2 drugs are bioequivalent if
**not sure about this**
they show comparable bioavailability and similar times to achieve peak blood concentration
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pharmacokinetics: how a drug gets out of your body
elimination
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oral penicillin is 10% bioavailable. your options are:
give 10x the dose orally, or give I.V.
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without blood flow to the site, you won't get
drug flow to that site.
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what is the concept of 'contact time' in terms of absorption?
with diarrhea, the drug will come right out. with gastroparesis, it will stay in too long.
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relevance of surface area to amount of drug
if you decrease surface area, you must increase the amount of drug. example: gastric bypass surgery, missing some stomach and some intestine. need more meds.
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pH in the context of absorption
the pH of the site is very important!
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transport: most drugs go by [passive diffusion or active transport]
passive diffusion. sometimes they need active transport, which requires ATP. but usually passive diffusion.
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route of administration: intrathecal
- directly into spine.
- good for anesthesia.
- rare.
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3 parenteral modes of administration (most predictable to least predictable)
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is direct IV access predictable?
yes, and fast. it hits the brain first.
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pharmacokinetics: how the drug gets in
absorption
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this is made by coagulase-negative staph in order to protect itself from antibiotics
biofilm. catheters just need to COME OUT.
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4 problematic sites of infection for antibiotic delivery
- CNS/eye/blood brain barrier
- Abscess
- poorly vascularized areas
- bone
-
a diplococcus (in 2's), major cause of lobar pneumonia. the magic is in its capsule: without the capsule it's powerless
- streptococcus pneumoniae
- aka pneumococcus
- aka strep pneumo
-
normal flora in oropharynx, GI and GU tracts. dental caries, subacute bacterial endocarditis
viridans streptococci
-
streptococcus makes these. they activate the immune system and make it go haywire. massive cytokine storm. necrotizing fasciitis is in there.
superantigens
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2 routes of non-renal clearance
bile (i.e. ceftriaxone)
intestine (i.e. azithromycin)
-
infection in the biliary tree
ascending cholangitis
-
if a drug is excreted in the bile, you don't want to use it to treat a
UTI
-
most common mechanism of clearance for antibiotics
renal clearance
-
destroys muscle, destroys fat. starts off as cellulitis
necrotizing fasciitis
-
disproportionate amount of pain; blood-filled bulla: assume this until proven otherwise
necrotizing fasciitis
-
unique superficial form of cellulitis (cellulitis proper is deeper). red, swelling, on the face
Erysipelas
-
impetigo: treat for strep or staph?
both
-
4 centor criteria
- 1. heart rate 100+
- 2. temp above 38C (104F)
- 3. no cough
- 4. positive sore throat
3 of 4? treat for strep A.
-
this comes from strep. pyogenes. it breaks down blood clots and RBCs. we use it for strokes.
streptokinase
-
the most important virulence factor for strep pneumo
capsule
-
who gets vaccinated for strep pneumo?
-
kind of hemolysis: green plate. RBCs intact. hemoglobin turns to biliVERDin
alpha hemolysis (this is not "true" hemolysis like beta)
-
gamma hemolysis
is a misnomer. no actual hemolysis at all.
-
true hemolysis. lysed blood cells! plate becomes clear where cells have been lysed.
beta hemolysis
-
same family as strep but lives in the gut
enterococci
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amoxicillin is given this way
orally
-
ampicillin is given this way
- IV
- you can give it orally but it must be dosed very frequently
-
MIC
minimum/mean inhibitory concentration. the concentration needed to inhibit growth. note: this doesn't assure safety, it might inhibit life, too.
-
-
percentage of drug that reaches the systemic circulation, of the total amount given
- bioavailability
- IV is 100% bioavailable because all the drug enters the bloodstream
-
"Drugs absorbed form the small intestine can be affected by metabolism from the liver as the venous circulation of the intestine drains into the portal circulation"
first pass effect
-
drug goes from portal vein into liver, metabolized and THEN spreads out into the body
first pass effect
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