Pharmacology Flashcards
What does AUC measure?
It measures bioavailability when the y-axis is Plasma Drug Concentration and the x-axis is time.
What is bioavailability?
The extent to which a drug is absorbed and reaches systemic circulation.
What is the variable “F”?
Bioavailability.
Bioavailability is the Fraction (F) of the drug is absorbed after any route of administration compared to IV administration which has a bioavailability of 100%. It can range from 1.0 (100%) to 0 (0%).
What are some factors that affect Bioavailability?
- Drug is unstable in GI tract bc of acid levels.
- Food in GI tract.
- Drug is charged and cannot pass thru GI mucosa.
- First Pass Effect: Drug is biotransformed as it passes through GI mucosa and liver.
Decreasing the rate of absorption does what to the pharmacokinetics?
Creates a slower rate of elimination and a longer duration of action.
What form are drugs in when using a patch?
Lipid soluble non-ionized.
What are the three routes a drug can use to cross a drug membrane?
Diffusion through lipids, diffusion through an aqueous layer, and using a carrier.
What is Ka?
Ionization constant.
Ka = [H+][A-]/[HA]
What is the log form of the Ka equation?
pH = pKa + log[A-]/[HA]
Is pKa a constant?
yes
How is the Henderson-Hasselbach equation different for acids and bases?
Acid: pH - pKa = log[ionized]/[nonionized]
Base: pH - pKa = log[nonionized]/[ionized]
How does pH affect the ratio of ionization?
Acids: high pH means more ionization.
Base: low pH means more ionization.
How can a drug cross the blood/brain barrier?
If it is lipid soluble.
What is the partition coefficient?
A measure of lipid solubility. A higher partition coefficient means more lipid soluble.
The kidney excretes drugs in what form?
Kidneys excrete drugs in their ionized form.
Is the pH of urine constant, and how does that affect drug reabsorption?
The pH of urine is variable. A weak acid drug (aspirin) will be less ionized in acidic urine, and therefore more likely to be reabsorbed. A drug that is a weak base will more likely be ionized in acidic urine, and therefore more likely to be excreted.
In acidic urine, what type of drug is excreted more quickly?
In acidic urine, basic drugs are excreted more readily.
What is the difference between a zero order and first order reaction?
Zero order is not dependent on drug concentration bc it’s absorption has to do with a mechanism that is fixed, such as gastric emptying. A first order reaction is dependent on the drug concentration bc it uses diffusion or some other reaction with a concentration gradient.
What is ED50
Dose required to produce a therapeutic effect in 50% of the population.
What is TD50?
Dose required to produce a toxic effect in 50% of the population.
What is the Therapeutic Index?
TD50/ED50
What is Kd and Ka?
Kd = dissociation constant = Koff/Kon
Ka = association constant = Kon/Koff
What’s the difference between PK and PD?
Pharmacokinetics: What the body does to the drug.
Pharmacodynamics: What the drug does to the body.
What is the equation for dose?
Dose = Concentration x Volume
Does a lipophilic drug have a larger or smaller apparent volume of distribution (V or Vd)?
Larger. It if is lipophilic it can be absorbed by fats; if it is only water soluble then it gets excreted in urine.
Other than lipid solubility, what else affects Apparent Volume of Distribution?
Plasma protein binding because it keeps the drug in the blood compartment.
What is the Elimination Rate Constant?
K = ln(2)/(half life)
What is Clearance?
Clearance = Dose/AUC
Time to steady state (ss) is dependent on what?
Half-Life.
What is the equation for finding the Maintenance Dose?
Maintenance Dose = V * (Cmax - Cmin)
How do you calculate the Maintenance Dose Interval?
Maintenance Dose Interval = 2.303/k * log(Cmax/Cmin)
What is the equation for Loading Dose?
Loading Dose = V * Cmax
What is the equation for Infusion Rate?
Infusion Rate (ko) = CL x C, or ko = V x k x C
k = elimination constant
What are the equations for an IV bolus and maintenance infusion?
Loading Dose (Bolus) = Css x V
Maintenance Infusion = CL x Css
What is genetic heterogeneity?
The different genotypes with the same phenotype.
What is allelic heterogeneity?
Different abnormalities at the same locus creating the same phenotype.
What is a founder’s effect?
Genetic diseases that are especially prevalent in a small populations, -ie Ty Sach’s Disease in the Ashkenazi Jews.
What is pleiotropy?
Mutant genes affect multiple organ systems.
What is penetrance?
of people with genotype and phenotype / # of people with genotype.
