Basic Pharmacology Flashcards
Km
inversely related to the affinity of the enzyme for its substrate.
Thus low Km = high affinity.
Vmax
Directly porportional to the enzyme concentration
Also known as the drugs efficacy.
Y intercept in a lineweaver burk plot
Vmax.
The greater the Y intercept, the lower the Vmax
The X intercept in a lineweaver burk plot
This is the Km
The greater the Km/ further to the right the lower the affinity.
Describe competitive inhibitors that are reversible.
Resemble the substrate, can be overcome by adding more substrate.
Will increase the Km and lower enzyme efficiency
This ultimately is lowering the potency.
Describe non competitive inhibitors
These bind separately from the active site and take the enzymes completely out of commision.
Thus they lower the Vmax but do not effect the Km
This is lowering the efficacy and cannot be changed by adding substrate.
Describe irreversible competitive inhibitors
These resemble the subsrate and bind the active site but cannot be removed or overcome by adding more substrate.
Thus they lower the Vmax and do not effect the Km. These lower efficacy.
What is bioavailability?
The fraction of the administered drug that reaches the systemic circulation unchanged.
For an IV dose F = 100%
What is the volume of distribution?
The ammount of drug that is in the body relative to its plasma concentration.
These are usually altered by the liver and kidney especially in diseases.
What would a low volume of distribution describe?
The drug is mostly found in the blood.
Think of large molecules and those that are bound to plasma proteins.
What would a medium volume of distribution describe?
This would be describin drugs that are limited to the ECF such as small, hydrophilic molecules.
What would a high volume of distribution describe?
All tissues including fat are saturated by the drug.
Think of small lipophilic molecules especially if they bind tissue proteins.
What is a drugs clearance?
The volume of plasma that is being cleared of the drug per unit of time.
Rate of elimination of drug/plasma concentration of drug.
How many half lives does a drug typically take before being fully eliminated from the body?
4-5 half lives
Describe zero order elimination of a drug
Rate of elimination is constant regardless of the plasma concentration. Think PEA Phenytoin Ethanol Aspirin
Describe first order elimination of a drug
Rate of elimination is directly proportional to the drug concentraton in the plasma.
This is a flow dependent elimination type.
Describe how you could treat an overdose of a weak acid drug.
Make the urine basic to trap the weak acids.
Examples would be phenobarbital, methotrexate, and aspirin.
Describe how you could treat an overdose of a weak basic drug.
Make the urine acidic with ammonium chloride.
And example of this would be amphetamines.
Describe phase I and phase II of drug metabolism
Phase I includes reduction, hydrolysis through cytochrome P-450. This phase is lost first in geriatric patients.
Phase II is then the conjugation (glucuronidation, acetylation, sulfonation) of drugs yielding polar inactive metabolites for renal secretion.
Slow acetylators have increased side effects from certain drugs.
Drug Efficacy
Vmax, maximal effect a drug can produce.
