Pharmacodynamics Flashcards
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
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
Formula:
CrCl=(140-age) x IBW/sRcR x 72 (all times 0.85 since female)
-The interval would be every 12 hours
