Pharmacology General Principles Part II Flashcards
Elimination
The process of making a drug pharmacologically inactive and removing it from the body
Includes metabolism and excretion
Is free drug or plasma protein bound drug filtered from the body?
Only free drug is filtered from the body while plasma protein bound drug remains in the body
Excretion formula
Excretion = Filtration - Reabsorption + Secretion
What is creatine clearance used to determine?
An approximate measure of renal function
If excretion = GFR
There is no absorption or secretion
If excretion < GFR
There is reabsorption
If excretion > GFR
There is secretion
Clearance mechanisms
Metabolism and Excretion are both clearance mechanisms
Clearance (CL) formula
Distribution phase of IV drug (graph)
Half life formula
How many half lifes for a drug to be eliminated from the body?
5 half-lifes which equals 95% of the drug removed from the body
Do most drugs follow first-order or zero-order kinetics?
~95% of drugs follow first-order kinetics
What are some common drugs that follow zero-order kinetics?
- Aspirin
- Ethanol
- Phenytoin
First-order elimination kinetics
- Elimination rate is diretcly proportional to the drug concentration
- Half-life is fixed
Zero-order elimination kinetics
- Rate of elimination is independent of drug concentration and occurs at a constant rate
- No half-life
Steady-state plasma drug concentration (Cp(ss))
When the rate of drug administration = rate of drug elmination
Purpose is to maintain a therapeutic dose
How many half lifes of the drug does it take to reach the steady-state plasma drug concentration?
It takes 1 half-life to reach 50% of the CP(ss)
And 5-6 half-lives tp reach 100% of the CP(ss)
Loading dose formula
When would we use a loading dose?
When it is necessary to achieve the therapeutic plasma concentration levels quickly
Maintenance dose and dosing rate forumula
Efficacy
Greatest effect an agonist can produce if the dose is taken to the highest tolerated level
Potency
- Amount of drug needed to produce a certain effect
- Affected by the affinity of the receptor for the ddrug and the number of receptors available
EC50/ED50
The concentration/dose of a drug required to produce a response in 50% of individuals
Efficacy and Potency chart
TD50
Dose required to produce toxicity in 50% of individuals
LD50
Dose required to produce a lethal response in 50% of individuals
Therapeutic index
TD50/ED50
Not a very goodd estimate of safety
Therapeutic Window
TD1/ED50
Range between ED50 and starting point of TD50 (which is TD1)
Range of drug dosages which can effectively treat the disease while staying with the safety range
Certain safety factor
TD1/ED99
Dose that produces minimum toxicity (toxicity in 1% of individuals)
And is effective in 99% of individuals
Agonist
Drug that binds to the drug-receptor and activates it
Partial agonist
Activates the receptor but does not produce the maximal response
Full agonist
Activates the receptor and produces the maximal response
Inverse agonist
Binds to the inactive state of the receptor and decreases the constitutive activity
Produces the opposite effect of the agonist
Competitive antagonists
Binds to the agonist receptor site in a reversible way without activating the effector system of that receptor
Non-competitive antagonists
Irreversible binding to the active site
or
Irreversible or reversible binding to the allosteric site
In either case, agonist cannot out compete the non-competitive antagonist
