Pharmacodynamics Flashcards
(25 cards)
Define Pharmacodynamics
Actions of a drug on the body
Name ex of Ligand-gated ion channel
Cholinergic nicotinic receptor
Name ex of G protein-coupled receptor
alpha and beta adrenceptors
Name example of enzyme-linked receptors
Insulin receptors (activation of tyrosine kinase)
Name example of intracellular receptors
Steroid receptors
- How do nicotinic receptors work?
Stimulation by Ach –>Na influx
- How do GABA receptors work?
Benzodiazepines ENHANCE stimulation of GABA receptors–>Cl influx
- How do G-protein coupled receptors work?
alpha subunit dissociates & activates adenyl cyclase
- How do enzyme-linked receptors work?
Binding of a drug to an extracellular receptor activates or inhibits enzymes
Define tachyphylaxis
repeated administration of a drug results in diminished effect
Explain the graded dose response curve
Incr. Concentration of drug = Incr. effects
Define potency
Amount of drug required to produce a given effect
Define Efficacy (intrinsic activity)
The ability of the drug to illicit a physiologic response when it interacts with a receptor
What is Kd?
Dissociation constant, used to determine affinity of a drug to a receptor. (Higher kd = lower affinity)
- Define competitive antagonist
binds to the same site as the agonist (competition for binding sites)
- Define irreversible antagonist
covalent bonds or binds at a different (allosteric) site
- Define functional antagonist
the antagonist causes opposing actions
*Give an example of a functional antagonist
Histamine binds to one receptor –> broncoconstriction; EPINEPHRINE binds to another receptor–>bronchodilation
- Define therapeutic index
Measurement of a drug’s safety
TD50/ED50
*Name CYP450 incucers
carbamazine, phenobarbital
*** (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?
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
***( 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?
-To calculate half life: 0.693 divided by K
Plug numbers in=5.8 hours half life
** (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.
-To calculate expected clearance:
Clerance =volume of distribution x K=20 x .12=2.4 liters/hour= 40 ml/min
Cl=k * Vd
** (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?
-It takes 4 half lives to reach steady state
Css=reached-4 half lives=5.8 x 4=23.4
