Pharmacodynamics

Question 1

Define Pharmacodynamics

Answer 1

Actions of a drug on the body

Question 2

Name ex of Ligand-gated ion channel

Answer 2

Cholinergic nicotinic receptor

Question 3

Name ex of G protein-coupled receptor

Answer 3

alpha and beta adrenceptors

Question 4

Name example of enzyme-linked receptors

Answer 4

Insulin receptors (activation of tyrosine kinase)

Question 5

Name example of intracellular receptors

Answer 5

Steroid receptors

Question 6

• How do nicotinic receptors work?

Answer 6

Stimulation by Ach –>Na influx

Question 7

• How do GABA receptors work?

Answer 7

Benzodiazepines ENHANCE stimulation of GABA receptors–>Cl influx

Question 8

• How do G-protein coupled receptors work?

Answer 8

alpha subunit dissociates & activates adenyl cyclase

Question 9

• How do enzyme-linked receptors work?

Answer 9

Binding of a drug to an extracellular receptor activates or inhibits enzymes

Question 10

Define tachyphylaxis

Answer 10

repeated administration of a drug results in diminished effect

Question 11

Explain the graded dose response curve

Answer 11

Incr. Concentration of drug = Incr. effects

Question 12

Define potency

Answer 12

Amount of drug required to produce a given effect

Question 13

Define Efficacy (intrinsic activity)

Answer 13

The ability of the drug to illicit a physiologic response when it interacts with a receptor

Question 14

What is Kd?

Answer 14

Dissociation constant, used to determine affinity of a drug to a receptor. (Higher kd = lower affinity)

Question 15

• Define competitive antagonist

Answer 15

binds to the same site as the agonist (competition for binding sites)

Question 16

• Define irreversible antagonist

Answer 16

covalent bonds or binds at a different (allosteric) site

Question 17

• Define functional antagonist

Answer 17

the antagonist causes opposing actions

Question 18

*Give an example of a functional antagonist

Answer 18

Histamine binds to one receptor –> broncoconstriction; EPINEPHRINE binds to another receptor–>bronchodilation

Question 19

• Define therapeutic index

Answer 19

Measurement of a drug’s safety

TD50/ED50

Question 20

*Name CYP450 incucers

Answer 20

carbamazine, phenobarbital

Question 21

*** (GO OVER)
A patient is given 100 mg of an anticonvulsant medication. The resulting plasma concentration is 5 mg/L. A therapeutic concentration is 10 mg/L. This drug follows first order kinetics and has an elimination rate constant of 0.12 hr-1
-What additional dose would be needed to reach a therapeutic concentration?

Answer 21

1st step: calculate volume of distribution
Divide dose by the concentration 100/5 =20 liters
2nd calculate what additional dose is need C2-C2 x volume of distribution?
Pt would need an additional 100 mg

Question 22

***( Go over)
A patient is given 100 mg of an anticonvulsant medication. The resulting plasma concentration is 5 mg/L. A therapeutic concentration is 10 mg/L. This drug follows first order kinetics and has an elimination rate constant of 0.12 hr-1
-What is the half-life for the drug?

Answer 22

-To calculate half life: 0.693 divided by K

Plug numbers in=5.8 hours half life

Question 23

** (Go over)
A patient is given 100 mg of an anticonvulsant medication. The resulting plasma concentration is 5 mg/L. A therapeutic concentration is 10 mg/L. This drug follows first order kinetics and has an elimination rate constant of 0.12 hr-1
-Calculate the expected clearance for this drug in ml/min.

Answer 23

-To calculate expected clearance:
Clerance =volume of distribution x K=20 x .12=2.4 liters/hour= 40 ml/min
Cl=k * Vd

Question 24

** (Go over)
A patient is given 100 mg of an anticonvulsant medication. The resulting plasma concentration is 5 mg/L. A therapeutic concentration is 10 mg/L. This drug follows first order kinetics and has an elimination rate constant of 0.12 hr-1
-If a continuous IV infusion is started with this anticonvulsant, how long would it take to reach steady state?

Answer 24

-It takes 4 half lives to reach steady state

Css=reached-4 half lives=5.8 x 4=23.4

Question 25

A 75 year old female with an IBW of 121 lb requires an antibiotic to treat an infection that requires dose adjustment based on renal function. Her most recent serum creatinine (SrCr) is 1.5. The dose is 1 gram IV, but the dosing interval is according to the chart below:

CrCl ≥ 60 ml/min – every 6 hoursCrCl 40-59 ml/min – every 8 hoursCrCl 20-39 ml/min – every 12 hoursCrCl

Answer 25

Formula:

CrCl=(140-age) x IBW/sRcR x 72 (all times 0.85 since female)

-The interval would be every 12 hours