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46 Cards in this Set
- Front
- Back
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Definition of Pharmacokinetics
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the quantitative study of the absorption
distribution metabolism Excretion ...of injected and inhaled drugs and their metabolites. |
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"What the body does to the drug..."
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Pharmacokinetics
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Definition of Pharmacodynamics?
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The study of the
intrinsic sensitivity or responsiveness of receptors to a drug and the mechanisms by which these effects occur. |
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"What the drug does to the body..."
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Pharmacodynamics
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Stereochemistry
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the study of how molecules are structured in three dimensions
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A molecule that has a center in a three dimensional form and is asymmetrical (right and left side)
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Chirality
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A pair of molecules existing in two forms that are mirror images of one another (right and left hand), but cannot be superimposed. (are chemically identical)
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Enantiomers
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when dissolved in solution , the entantiomer rotates polarized light clockwise.
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Dextrorotatory (+)
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When dissolved in solution, the enantiomer rotates polarized light counterclockwise.
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Levorotatory (-)
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Racemic mixture
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When two enantiomers arepresent in equal proportions. (does not rotate polarized light because the optical activity of each is cancelled out)
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Examples of racemic mixtures in anesthesia.
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Thiopental,
methohexital, ketamine |
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What factors affect the potency of a drug?
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1. Absorption
2. distribution 3. metabolism 4. excretion 5. affinity |
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What is ED50?
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The dose required to produce a specified effect in a given percentage of patients (50%)
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Determinants of tissue uptake of a drug?
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1. blood flow
2. Concentration gradient 3. Blood-brain barrier 4. physicochemical properties of drug: - ionization - lipid solubility - protein binding |
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Determinants of capacity of tissue to store drug?
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1. Solubility
2. Tissue Mass 3. Binding to macromolecules(proteins) 4. pH |
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Awakening after a single dose of thiopental principally reflects what pharmacokinetic principle?
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Redistribution of drug from brain to less perfused tissue sites (muscles, etc.)
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What determines uptake of a drug?
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Blood flow
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What are the determinants that increase the diffusibility of a drug accross cell membranes?
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1. Nonionized
2. lipid soluable 3. unbound to protein |
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What determines central nervous system distribution of a drug?
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Blood brain barrier
(BBB can change and be overcome by large doses of drug, acute head injury, and hypoxemia) |
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How is the volume of distribution of a drug calculated?
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Dose of drug administered /plasma concentration of drug(before elim)
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What influences Vd (vol of distribution)?
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1. lipid solubility
2. protein binding 3. molecular size |
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What determines uptake of drugs by the tissue?
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1. amount of blood flow to tissue
2. Concentration gradient accross the membranes |
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What are the properties that influence Pharmokinetic activity?
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1. Molecular size (Smaller = crosses)
2. Degree of lipid solubility (More = crosses) 3. Degree of ionization (Nonionized = crosses) 4. Protein bound (unbound= crosses) |
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Acids are
a) proton donors b) proton acceptors |
Acids are proton donors
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Bases are
a) Proton donors b) Proton acceptors |
Bases are proton acceptors
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Ionized forms of drugs are hydrophilic? T or F
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True, Ionized forms of drugs are water soluble(hydrophilic) and Unionized drugs are lipophilic.
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When the pH - pKa of an acid drug is less than zero what happens?
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the degree of nonionized drug is greatest.-more free drug ("acids like acids" -or more drug available)
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When the pH - pKa of a base drug is less than zero, what happens?
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the degree of ionized drug is greatest -less free drug (Bases like bases -or =more drug available)
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What is ion trapping?
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When the uncharged (unionized) form of the drug crosses the membrane to a more acidic environment, becomes ionized and becomes "trapped"in this compartment and cannot move back across the membrane.
[ex: GI system, maternal-fetus, infected tissue] |
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What is the most abundant protein involved in protein-binding of a drug?
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Albumin (favorably binds to acidic compounds more than basic)
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What is the consequences of extensive protein binding of drugs?
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Affects drug distribution (prevents drugs from binding to receptors)
Affects the amount of drug that is free to enter tissues. |
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What is Bioavailability?
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The extent to which a drug reaches its effect site after its introduction into the circulation system.
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What is the central compartment in the compartment model of pharmokinetics? (used to calculate the Vd)
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Central compartment: (10%mass-75% of CO)
-intravascular fluid -heart -lungs -brain -liver -kidneys Peripheral compartment: (90% body mass, 25% CO) -muscle, fat and bone |
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How do drugs leave the central compartment?
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1. metabolism (dist to tissues)
2. Excretion (kidneys, liver..) |
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What is Volume of Distribution (Vd)?
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Dose of the drug given divided by the plasma concentration of the drug.
Used to calculate the loading dose that will achieve a steady-state concentration. |
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A drug with a large volume of distribution (thiopentathal) has low concentrations in the plasma and very little drug available to the organs for elimination.
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True
... the highly lipid soluble drug is distributed quickly to peripheral tissue, thereby ending its action more rapidly than its elimination half-life would predict. |
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What is steady state?
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The all body compartments equilibrate with the circulating agent or drug, drug elimination is equal to the rate at which the drug is made available.
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What is the goal of metabolism?
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To change lipid-soluble agets into more water-soluble forms so that the kidneys can eliminate them.
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Drugs that undergo Phase 1 Hydrolysis?
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(cholinesterase Catalyzed)
Succinylcholine Cocaine & Procaine Chloroprocaine & tetracaine Neostigmine Edrophonium & Pyridostigmine |
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What is Phase 1 Reactions?
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Oxidation -Hydrolysis Reduction
--end result is a more polar compound that is easily excreted by the kidneys |
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What is Phase II reactions?
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Synthetic reactions because the body actually synthesiszes a new compound by donating a functinal group.
(Conjugation) |
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What is elimination half-life(T 1/2) ?
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The time necessary for the plasma content of a drug to drop to half of its prevailing concentatiion after a rapid bolus injection.
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How many half-life s does it take to eliminate over 96% of drug from body?
(first order kinetics) |
5 (it is considered fully eliminated when app 95 % is elim)
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What is zero-order elimination?
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a constant amount (not percentage) is eliminated over time
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What is context-sensitive half-time?
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the time to halving of the blood concentration after termination of a drug admin by an infusion designed to maintain a constant concentration.
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Perfusion-dependent elimination?
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Drugs with a High Extraction Ratio of 0.7 or greater- rely on hepatic blood flow for clearance, so a decrease in hepatic bld flow decreases the rate of clearance., and an increase in Bld Flow increases clearance.
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