pharmacokinetics I and II Flashcards
(35 cards)
what is absorption?
movement of drug from site of admin to blood
what is distribution?
delivery of drug from blood to tissues
what is bioavailability?
amount that actual reaches the target in biologically active form after crossing lipid membranes, binding proteins, tissue storage, metabolism, excretion
what is the partition coefficient?
how much a drug likes fat vs water, higher number represents how much drug is in fat vs water.
Pka rule of thumb
lower an acids pka the stronger it is, higher a base’s pka the stronger it is
ionization rule of thumb
bases are ionized in acidic environment (BH+)
acids are ionized in basic environment (A- + H+)
absorption in mouth
- drugs with high partition coefficient and favorable pka
- absorption 4 times faster than in GI, but passage is fast
absorption in stomach
- only weak acids
- most drugs are weak bases
absorption in small intestine
mostly by first 1-2 meters of proximal jejunum
why are pH and pka so crucial in small intestinal absorption?
diffusion is passive
large intestine absorption
not as much as small intestine, not as vascularized
why do suppositories work?
rectal blood doesn’t go straight to liver
absorption in lung
highly vascularized, high surface area, lipophilic so favors high partition coefficient, many things can get in through the lungs
advantages of IM or SC injection
rapid, precise, large volumes,
disadvantages of IM or SC injection
pain, necrosis, nerve damage
advantages of IV
direct, good for narrow TI, good for those with low absorptive capacity
disadvantages of IV
- easier to overdose
- risk of embolism or microbial contamination
- local necrosis or immune reaction
drug accumulation in five places in the body
1) kidney - highly susceptible to toxicity due to high blood flow
2) eye - melanin can bind drugs
3) fat - high partition coef, slow in slow out
4) lung - accumulates basic amines
5) bone - VERY slow in and out
what is K-el?
time constant for drug elimination
how is K-el related to half life?
K-el = .693 / half life or half life = .693/K-el
what is Co?
initial concentration of the drug
what is Vd and its formula?
volume of distribution
Vd = D (dose)/Co (initial concentration)
what is Clp? what is its formula?
Clp (clearance) = K-el (elimination constant) x Vd (volume of distribution)
what is Css?
steady state concentration, what you are trying to maintain with a maintenance dose.
