pharm pharmacokinetics and pharmaodynamics

Question 1

Michaelis Mentin kinetics

Answer 1

As the concentration of the substrate increases, the velocity of the reaction increases to a point

Question 2

Km

Answer 2

Km is the substrate concentration at which the velocity of the reaction is half the Vmax; Km is inversely related to the affinity of the enzyme for the substrate

Question 3

Lineweaver-Burk plot

Answer 3

On the y axis is 1/V, and on the x axis 1/[S];

Question 4

Competitive versus noncomp inhibitors

Answer 4

competitive bind the active site, are overcome by increased substrate, don’t affect the Vmax, increase Km; noncompetitiv inhib are not overcome by increase in substrate, don’t bind the active site, decrease the maximum velocity of the reaction, no effect on Km

Question 5

bioavailability

Answer 5

fraction of administered drug reaching systemic circulation unchanged; For IV, it is 100%

Question 6

Which drugs have a low volume of distribution

Answer 6

Those that just stay in the blood; large/charged molecules, or those that are plasma protein bound

Question 7

Which drugs have a medium volume of distribution?

Answer 7

Those that go into the ECF, small hydrophilic molecules

Question 8

Which drugs have a high volume of distribution?

Answer 8

Those that go into all tissues including fat; these are small lipophilic molecules, esp if bound to tissue protein

Question 9

Clearance formula

Answer 9

CL= rate of elim of drug/(plasma drug concentration)= Vd x Ke (elim constant)

Question 10

Half life formula

Answer 10

t(1/2)= 0.693 x Vd/ CL

Question 11

Loading versus maintenance dose

Answer 11

In renal or liver disease, maintenance dose decreases and loading dose is usually unchanged

Question 12

Time to steady state depends on what?

Answer 12

primarily on the half life, and is independent of the dose and dosing frequency

Question 13

Zero order elimination

Answer 13

rate of elimination is constant regardless of Cp (target plasma concentration at steady state); Examples are phenytoin, ethanol, and aspirin (at high or toxic concentrations)

Question 14

First order elim

Answer 14

Rate of elim is directly proportional to the drug concentration

Question 15

Urine pH and drug elim

Answer 15

Charged species are trapped in the urine and eliminated more quickly; neutral forms can be reabsorbed

Question 16

Treat overdose of a weak acid with bicarb- why?

Answer 16

It pulls of the H+ and makes it charged and cleared by the kidneys

Question 17

Phase I versus Phase II drug metabolism

Answer 17

Phase I is reduction, oxidation, hydrolysis with cyp450, often yielding slightly polar water-soluble metabolits; then phase II is conjugation (glucuronidation, acetylation, sulfation), usually yielding a very polar inactive metabolite that is renally excreted; Note that geriatric patients lose Phas 1 first

Question 18

Efficacy

Answer 18

max effect a drug can produce; Increaed Vmax means increaesd efficacy; partial agonists have less efficacy than full agonists

Question 19

potency

Answer 19

amount of drug needed for a given effect. Increaesd potency means less of the drug is needed. Represented by the EC50 (x value)

Question 20

Competitive antag

Answer 20

Need more of the agonist to achieve the same effect; the maximum effect is still the same; decreases the potency; shifts the curve right; flumazenil is a competitive antag of diazepam on the GABA receptor

Question 21

Noncompetitive antag

Answer 21

The maximum effect is decreased; decreases efficacy; shifts the curve down; phenoxybenzamine is a noncomp antag of norepi

Question 22

Partial agonist

Answer 22

Decreases the maximum effect that can be achieved; decreases efficacy; potency not affected; buprenorphine is a partial agonist at opioid mu receptors

Question 23

Therapeutic index

Answer 23

Measurement of drug safety; median toxic dose/median effective dose;