Chapter 2: Pharmacology Flashcards
equation for volume of distribution
Vd = total in body/ [drug in plasma]
Drugs with low Vd are found where, vs. with high Vd?
low Vd- in plamsa
high Vd- all tissues
A new drug is found experimentally to have an apparent Vd of 2000 L in a 70-kg adult. What is your interpretation of these data?
High Vd means it is sequestered in the tissues to great extent
Would hemodialysis be an effective way to eliminate a drug with high Vd?
No; it is only goodd for low Vd
Interpret a drug’s clearance being GFR
less than gfr– being reabsorbed in distal tubule
> gfr– being secreted actively
For a drug with a t 1/2 of 3 hours given by constant IV infusion, how long will it take for this drug to reach 75% of steady state?
2 half lives: 6 hours
Loading dose or Maintenance dose? Must know clearance to calculate
MD. (key distinction)
Loading dose or Maintenance dose? Must know volume of distribution to calculate
LD (key distinction)
Loading dose or Maintenance dose? Usually administered in a single bolus
LD
Loading dose or Maintenance dose? Most useful in emergency situations
LD
Loading dose or Maintenance dose? Given to achieve steady-state plasma levels over time
MD
Identify 3 drugs whose elimination represents a constant amount over time
Phenytoin
Ethanol
Aspirin at very high doses
This is zero-order kinetics
Weak acids and bases and their dissociation. What crosses the membrane and what is better cleared?
Acid: R-COOH crosses the membrane, R-COOH- and H+ better cleared
Base: RNH3+ is better cleared, RNH2 + H+ crosses the membrane
(polar one is water soluble)
Drug #1 is a weak acid with PKa of 4. When placed at pH of 7.4 or pH of 2, will it be mostly ionized or non ionized? Will it cross the membrane easily or not?
At 7.4 it will be ionized and not cross the membrane
At 2 it will be nonionized and will cross the membrane
Drug #2 is a weak base with a PKa of 8. When placed at a pH of 7.4 or pH of 9, will it be mostly ionized or non ionized? Will it cross the membrane easily or not?
At pH of 7.4 it would be ionized and not easily cross membranes
At pH of 9 it would be nonionized and would cross membranes
What type of metabolism? reduced activity in neonates
glucoronidation
What type of metabolism? cytochrome p-450 metabolism
oxidation (phase I)
What type of metabolism? genotypic variation may cause SLE
acetylation
What type of metabolism? metabolism of chloramphenicol
glucoronidation
What type of metabolism? Metabolism of hydralazine
acetylation
P-450 inducer or inhibitor? phenytoin
inducer
P-450 inducer or inhibitor? erythromycin
inhibitor
P-450 inducer or inhibitor? grapefruit juice
inhibitor
P-450 inducer or inhibitor? phenobarbital
inducer
P-450 inducer or inhibitor? cimetidine
inhibitor
P-450 inducer or inhibitor? ritonavir
inhibitor
When given to a patient already receiving a full agonist, what effect will a competitive antagonist have on potency and efficacy?
decrease potency
no effect on efficacy
When given to a patient already receiving a full agonist, what effect will a noncompetitive antagonist have on potency and effficacy?
no effect on potency
decreases efficacy
Therapeutic index. Do we want it to be high or low?
The most dangerous drugs have a lower TI (digoxin, warfarin, etc.), whereas safer drugs have a higher TI.
