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What are 2 types of nonreceptor antagonists?
- chemical antagonist
- physiologic antagonist
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may either bind a molecule at some point in the activation pathway or directly inhibit the agonist. An example of this type of antagonism is local anesthetic agents which block sodium channels in th activation pathway of chemicals that promote depolarization of nerve fibers, so the pt will not feel pain
chemical antagonist
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activates pathways that oppose the action of tha agonist. An example is the action of epinephrine (vasoconstriction) on blood vessels; it overcomes the effect of histamine (vasodilation) on the same blood vessel.
physiologic antagonist
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drugs that have both agonistic and antagonistic properties.
mixed agonist-antagonists
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when mixed agonist-antagonists are used alon, the drug behaves as a what?
agonist
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when a mixed agonist-antagonist is used with another drug that competes for the same receptor site concurrently, the agonist-antagonist will also act as a what?
antagonist
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What are 2 ways receptors are classified?
- according to the type of drug they interact with
- specific physiologic response produced by the drug-receptor complex
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How can receptor sites be subclassified?and what is an example?
- by evaluating the effects of different agonists in the presence of a given antagonist
- epinephrine can bind to receptors in the bronchioles of the lungs to cause bronchodilation, and can bind to different receptors on blood vessels to cause vasoconstriction; hence one drug can interact with two different receptors and cause 2 different actions
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the number of any given receptor types or subtypes on a cell can vary; what illustrates this concept?
developing tolerance to a drug so the former dose no longer causes and adequate effect and a higher dose is neede to cause the effect
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the undesirable effects associated with the administration of therapeutic dosage of drugs; any drug at high enough concentration can produce a _____ effect (overdose)
toxicity
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What are 2 specific adverse effects of toxicity?
- exaggeration of direct effects seen at higher doses
- multiple concurrent adverse, or side effects occurring at therapeutic dosage levels
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What is an example of exaggeration of direct effects of therapeutic drugs seen at higher doses?
barbiturates may produce sedation, drowsiness and reduced rate of respiration at therapeutic levels, but can cause death at increased dose levels; an extension of the intended therapeutic effect of CNS depression
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What is an example of multiple concurrent adverse affects occurring at therapeutic dosage levels?
administration of certain antihistamines for hay fever, intended to antagonized histamine action at receptor sites in the respiratory system and can cause drowsiness; the drowsiness is a concurrent side effect, not an intended response
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Dose required to produce a desired response in 50% of the individuals within the same population
Median Effective dose (ED50)
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The dose that produces death in 50% of individuals
Lethal dose (LD50)
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a steep dose-response curve indicates what?
a narrow dose range (between the minimal and maximal effects; the risk for toxic or even lethal dosage levels can be greater)
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The actual ration of the LD50 and ED50; the margin of safety of a drug
Therapeutic index (TI)
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The higher the numeric value of the TI, the what?
safer the drug
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deals with the movement of drugs through the body.
pharmacokinetics
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What 5 aspects of the body do pharmacokinetics relate to?
- a drug's:
- absorption
- distribution in the body
- distribution to the site of action
- metabolism to prepare the drug for removal from the body
- excretion
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Where must most drugs pass through to produce an effect? What does this passage affect?
- through cell membranes to gain access to their receptors
- the amount of the drug that reaches the site of action and influences the time it takes the drug to get to the site of action
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What are 3 physiocochemical properties that influence the movement of drug mulecules across biologic membranes?
- molecular size
- lipid solubility
- degree of ionization
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__________ molecules are able to pass through lipids easily
nonionized
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the degree of ionization depends on what?
the pH at site
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In an acid environment, an acidic drug exists mainly in the _________ form. In the same acid environment, a vasic drug exists mainly in the __________ form
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__________ drugs are water soluble and must pass through water pores of the biologic membrane or be transported through the membrane by specialized transport mechanisms
ionized
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What are 3 different ways that ionized molecules are transported?
- filtration
- passive diffusion
- specialized transport mechanisms
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small, water-soluble substances may pass through aqueous channels or water pores in cell membranes by a process known as what?
filtration
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What must larger water-soluble molecules rely on to move through the biologic membrane?
specialized transport mechanisms
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Most drugs are weak acids or weak bases, and drug molecules are too large to pass through most aqueous channels, however, as a function of their lipid solubility, the nonpolar (nonionized) forms of these drugs readily can cross biologic membranes by ___________________ along a concentration gradient (from high concentration to low concentration) until equilibrium is reached across the membrane.
passive diffusion
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What are 2 different forms of specialized transport mechanisms that large ionized water-soluble drug molecules require to cross the biologic membrane?
- facilitated diffusion
- active transport mechanisms
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concept that assumes that the drug forms a complex with a component of the cell membrane on one side; the complex is then carried through the membrane, the drug is released, and the carrier returns to the original surface to repeat the process.
facilitated diffusion (specialized transport mechanism)
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the movement of drug molecules across biologic membranes against both a concentration gradient and an electrochemical gradient; it requires energy
Active transport (specialized transport mechanism)
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