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26 Cards in this Set
- Front
- Back
What type of drugs are the sulfonamides
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Broad spectrum, bacteriostatic drugs. Can treat both bacteria and parasitic diseases
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What does sulfanilamide do
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It is an inhibitor of folic acid synthesis in bacteria. It is a competitive inhibitor of dihydropteroic acid synthetase
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What is the mechanism of sulfonamide selective toxicity
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Animals obtain folic acid from their diet, while bacteria must metabolize it. Also, folate is not transfered into bacterial cells
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What does Trimethoprim do
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It acts as a competitive inhibitor of dihydrofolate reductase, which converts dihydrofolate into tetrahydrofolate (folic acid)
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What is the selective toxicity of trimethoprim due to
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Structural differences between bacterial and host dihydrofolate reductases. Bacterial enzymes have much higher affinity for the drug
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How is synergism achieved with sulfonamide and trimethoprim
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Sulfonamides inhibit new synthesis and folic acid, and trimethoprim prevents conversion of dihyrofolate to tetrahydrofolate. This double punch immediately delays growth
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What are the characteristics of Para-aminosalicylic Acid (PAS)
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Mechanism of action similar to the sulfonamides, but different spectrum of action. Effective against Mycobacterium tuberculosis. Difference reflects the differential sensitivities of the individual dihydropteroic acid synthetases.
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What antibiotics affect nucleic acid synthesis
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Rifampin, Rifabutin, Quinolones
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What does Rifampin do
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Inhibits RNA synthesis in bacteria. Narrow spectrum, bactericidal. Treats gram positive Neisseria sp. and mycobacteria. Prevents initiation of transcription, but does not inhibit transcription in progress
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Why are mitochondria not affected by Rifampin
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They contain a DNA-dependent RNA polymerase that is sensitive to the drug, but their membranes are impermeable to it
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Rifabutin is a derivative of Rifampin. What does it treat
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Infections caused by Mycobacterium avium
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What do the quinolone antibiotics do
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Inhibit bacterial DNA synthesis by specifically inhibiting the DNA gyrase of prokaryotic organisms.
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What are some of the quinolones
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Nalidixic acid (narrow spectrum, acts against gram-negative organisms in the urinary tract); Norfloxacin, Ciprofloxacin, Ofloxacin, Levofloxacin, Lomefloxacin, Sparfloxacin
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How do bacteria resist the quinolones
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Mutate DNA gyrase or alter the porins of gram-negative bacteria
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What antibiotics affect cell membranes
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Polymyxins, Colistin (polymyxin E), Amphotericin B
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What type of drugs are Polymyxins and Colistin (Polymyxin E)
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Bactericidal, narrow spectrum against gram negative bacteria (Pseudomonads in urinary tract infection).
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How do the Polymxins and Colistin (polymyxin E) work
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They contain a lower molecular weight ring with a hydrophobic tail. They insert into the membrane and bind PE or LPS, causing the membrane to become leaky. Active against growing and nongrowing cells
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What is resistance to Polymxins and Colistin (polymyxin E) due to
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Alterations in the outer membrane
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What is the selective toxicity of polymyxins and colistin (polymyxin E) due to
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Absence of PE and LPS in host cell membranes
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Why type of drugs are Amphotericin B and Nystatin
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Antifungals
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How is amphotericin B administered
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Intravenously for the treatment of systemic mycoses, since it is poorly absorbed through the gut
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How does Amphotericin B work
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It associates with ergosterol to form a channel through which molecules leak out of the cell
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Why does Amphotericin cause toxic side effects
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It binds to cholesterol as well as ergesterol, though with a lower affinity
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What are some of the negative aspects of amphotericin chemotherapy
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Toxic sides effects, such as nausea, vomiting, diarrhea, neprotoxicity, and anemia
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Why are the polymyxins primarily effective against gram-negative bacteria
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Gram-negative bacteria do not have a complex peptidoglycan layer to protect the cell membrane
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Why are the polyene antibiotics ineffective against bacteria
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Bacterial cell walls do not contain Ergosterol
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