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62 Cards in this Set

  • Front
  • Back
The ability of a chemical or drug to reach the site of action
What is bioavailability influenced by?
membrane permability and metabolic phenomena
What are some membrane barriers the drug must cross to reach the site of action?
GI mucosa, lung mucosa, the lymphatic or capillary wall, the intercellular substance, and the cell wall
How do most drugs cross the membranes?
simple diffusion according to Fick's law
What does diffusion depend on?
permeability, surface and concentration gradients
What do oral doses require to cross the membrane?
disintegration and dissolution
Which form are the drugs more lipid soluble in and diffuse more readily across the membrane?
unionized form (weak acid)
What occurs after the unionized form passively crosses cell membranes?
10 fold changes in concentration might occur for each unit pH change
Which form does the acidic stomach prefer?
the unionized form
Which form does the more basic small intestine prefer?
the ionized form
What is the most common place for pH and lipid solubility fo affect drug absorption?
across the gastrointestinal tract following oral administration
What effects the efficiency of oral administration of a drug?
1) lipid solubility
2) surface area
3) hepatic metabolic enzymes
What is drug elimination influenced by?
pH and lipid solubility
What happens when there is relative acidity of distal tubular urine?
there is a tendency to increase the ionization of weak bases thereby hastening their renal elimination wherease weak acids tend to passively diffuse back into circulation
What does breast milk tend to do to drugs?
concentrate weak bases
What is the only type of drug that can transport across the blood brain barrier?
lipid soluble drugs in unionized forms at body pH
What limits drug passage from the plasma to the CNS?
1) arachnoid villi via CF
2) enhanced high CNS blood flow
3) special active transport systems
4) Plasma protein binding
Which molecules pass poorly through the placenta?
1) highly charged molecules and other quaternary amines
2) large molecules
What is the principal of first order?
The absorption occurs at a diminishing rate that is always proportional to the amount of drug still to be absorped
zero order kinetics
at a constant rate independent of the amount of drug to be absorbed
What is t1/2?
The time required for half of the drug to be absorbed
What does t1/2 equal?
t1/2 = .693/k
Which process do drugs given by infusion follow? like an IV
zero order process, linear
What may effect the rate of drug distribution throughout the body?
binding of drug to plasma proteins
What do acidic drugs commonly bind to?
What do basic drugs often bind to?
glycoprotein or lipoprotein
What three factors effect binding?
1) plasma protein concentration with a number of receptor sites for binding
2) binding affinty constant between drug and protein
3) drug concentration
What does the extent of distribution of a drug within the body depend largely upon?
1) its ability to pass through cell membranes
2) changes in compartmental pH
3) binding to cell or plasma proteins
What is the equation for volume distribution?
Vd = Dose/Co
Which drugs have small Vd and which have large Vd?
acidic drugs have small, basic drugs have large
What is the major route of elemination for the great majority of drugs?
renal excretion
The time course of apperance of drug in the urine due to renal excretion will be linear or exponential?
If the elimination half life is quite long and it is necessary to fill up the body with drug to the desired plasma concentration quickly, what is that called?
the loading dose
What does the loading dose equal?
Loading dose = Vd (volume of distribution at steady state) * C (desired concentration)
What is defined as clearance of a drug?
the volume of plasma effectively cleared of drug by elimination (metabolism and excretion) per unit time
What two things does the half life depend on?
1) clearance
2) volume of distribution
What is the equation for clearance?
CL = Ke * Vd
What is the area under the curve?
estimated as cumulative areas of trapezoids, reprents the total drug that passed through the body
What must a drug satisfy to be approved by the FDA?
effectiveness and safety
What is ED50?
The dose at which 50% of the population reaches the desired effect
What is LD50?
The dose at which 50% of the population answers yes to the desired question
What is the theraputic index?
Ratio between the theraputic effects and side effects TI= LD50/ED50
What is an agonist vs an antagonist?
An agonist binds to a receptor and induces a change that leads to a biological response but an antagonist binds to a receptor and produces no change in the response
What are the common characteristics of receptors?
1) Saturability
2) High affinity
3) Reversibility
4) Specificity
What is drug potency proportional to?
receptor affinity
What effects drug potency?
bioavailability and metabolism
What is efficacy proportional to?
the maximal response to the drug
The larger the K the larger the?
affinity of the drug
What is often proportional to ED50?
Kd the dissociation constant
What is the langmuir equation?
Effect = (d) * Emax/ (d) + Kd
What is the Kd if the drug is half as potent?
the Kd is double
Difference between receptors and enzymes?
1) drug receptors do not metabolize their drugs
2) enzymes bind substrate and convert into product
3) receptors bind drug and receptors themselves change confirmation which produces intracellular transduction response
What is a competitive antagonist drug?
directly competes with the agonist for binding site, physiological effect gained by preventing agonist from stimulating receptor
What is an allosteric noncompetitive antagonist?
binds to a site distal from the agonist binding site and changes the conformation of the receptor so that agonist cannot bind
What is an irreversible noncompetitive antagonist?
binds in site normally occupied by agonist and forms a permanent covalent bond inhibiting binding of agonist
Is there a direct measurable effect of an antagonist?
What does increased amount of antagonist do to the curve?
shifts it more right so ED50 goes up but same effect value
What does a noncompetitive antagonist do to the curve?
the maximum effect has been lowered and the ED50 stays the same
Is receptor occupancy always proportional to the response?
How do you define the efficacy of partial agonist drugs?
with alpha
What can you have with chronic agonists? receptor overstimulated
1) desensitization
2) down regulation of number of receptors
What can you have with chronic antagonists/denervation? receptor chronically understimulated
1) supersensitivity
2) up regulation of the number of receptors