USMLE Step 1 First Aid 2015 Microbiology – Antibiotics – Flashcards
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Inhibits DNA TOPOISOMERASES
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Fluoroquinolones: Ciprofloxacin, norfloxacin, levofloxacin, ofloxacin, moxifloxacin, gemifloxacin, enoxacin
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Damages DNA
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Metronidazole
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Metronidazole, Clinical Use
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Giardia, Entamoeba Trichomonas, Gardnerella vaginalis Anaerobes (Bacteroides, C. difficile) H. pylori (Triple therapy with proton pump inhibitor and clarithromycin)
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Fluoroquinolones, Clinical Use
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Gram-negative rods of urinary and GI tracts: - Pseudomonas - Salmonella typhi Neisseria some gram-positive organisms Mycoplasma pneumoniae
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Inhibit FOLIC ACID SYNTHESIS (DNA methylation)
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Trimethoprim Sulfonamides: - Sulfadiazine - Sulfamethoxazole - Sulfisoxazole
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Sulfonamides, Clinical Use
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Gram-positives, Nocardia gram-negatives, Chlamydia Triple sulfas or SMX for simple UTI
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Inhibits mRNA SYNTHESIS (RNA polymerase)
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Rifampin
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Rifampin, Rifabutin, Clinical Use
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Mycobacterium tuberculosis Delay resistance to dapsone when used for leprosy. Meningococcal prophylaxis and chemoprophylaxis in contacts of children with Haemophilus influenzae type B. Rifabutin: - M. avium-intracellulare: Can add rifabutin or ciprofloxacin to usual treatment.
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Trimethoprim, Clinical Use
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Used in combination with sulfonamides (trimethoprim-sulfamethoxazole [TMP- SMX]), causing sequential block of folate synthesis. Combination used for UTIs Shigella Salmonella Pneumocystis jirovecii pneumonia treatment and prophylaxis toxoplasmosis prophylaxis
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Inhibit Protein Synthesis - 50S Subunit
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Chloramphenicol Clindamycin Linezolid Macrolides: - Azithromycin - Clarithromycin - Erythromycin Streptogramins: - Dalfopristin - Quinupristin
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Inhibit Protein Synthesis - 30S Subunit
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Aminoglycosides: - Amikacin - Gentamicin - Neomycin - Streptomycin - Tobramycin Tetracyclines: - Doxycycline - Minocycline - Tetracycline
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Chloramphenicol, Clinical Use
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Meningitis (Haemophilus influenzae, Neisseria meningitidis, Streptococcus pneumoniae) Rocky Mountain spotted fever (Rickettsia rickettsii). Limited use owing to toxicities but often still used in developing countries because of low cost.
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Clindamycin, Clinical Use
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Anaerobic infections (e.g., Bacteroides spp., Fusobacterium, Clostridium perfringens) in aspiration pneumonia, lung abscesses, and oral infections. Also effective against invasive group A streptococcal infection.
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Macrolides, Clinical Use
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Atypical pneumonias (Mycoplasma, Chlamydia, Legionella), STIs (Chlamydia), gram-positive cocci (streptococcal infections in patients allergic to penicillin), and B. pertussis. Azithromycin: - HIV - M. avium-intracellulare Prophylaxis when CD4+ count < 50 cells/mm3. - M. avium-intracellulare Treatment: Azithromycin or clarithromycin + ethambutol. - Babesia ( + atovquone) Clarithromycin: - H. pylori triple therapy: proton pump inhibitor + clarithromycin + amoxicillin (or metronidazole if penicillin allergy) - HIV - M. avium-intracellulare Prophylaxis when CD4+ count < 50 cells/mm3. - M. avium-intracellulare Treatment: Azithromycin or clarithromycin + ethambutol. Erythromycin: - Erythromycin ointment prevents neonatal transmission - Motilin receptor agonists (e.g., erythromycin) are used to stimulate intestinal peristalsis.
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Linezolid, Clinical Use
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Gram-positive species including MRSA and VRE.
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Tetracyclines, Clinical Use
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Borrelia burgdorferi M. pneumoniae Drugs' ability to accumulate intracellularly makes them very effective against Rickettsia and Chlamydia (+ Lymphogranuloma venereum) Also used to treat acne.
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Aminoglycosides, Clinical Use
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Severe gram-negative rod infections (e.g. Pseudomonas aeruginosa). Synergistic with β-lactam antibiotics. Neomycin for bowel surgery.
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Inhibit PEPTIDOGLYCAN CROSS-LINKING
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Penicillinase-sensitive penicillins Penicillinase-resistant penicillins Antipseudomonals Cephalosporins (I-V) Carbapenems Monobactams
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Inhibit PEPTIDOGLYCAN SYNTHESIS
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Glycopeptides: - Bacitracin - Vancomycin
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Penicillin G, V, MECHANISM
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Bactericidal Penicillinase sensitive Bind penicillin-binding proteins (transpeptidases). Block transpeptidase cross-linking of peptidoglycan in cell wall. Activate autolytic enzymes.
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Penicillin G, V, CLINICAL USE
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Gram-positive organisms (S. pneumoniae, S. pyogenes, Actinomyces) Gram-negative cocci (mainly N. meningitidis) Spirochetes (namely T. pallidum).
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Penicillin G, V, TOXICITY
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Hypersensitivity reactions, hemolytic anemia.
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Penicillin G, V, RESISTANCE
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Penicillinase in bacteria (a type of β-lactamase) cleaves β-lactam ring.
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Amoxicillin, ampicillin
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Bactericidal Penicillinase sensitive Bind penicillin-binding proteins (transpeptidases). Block transpeptidase cross-linking of peptidoglycan in cell wall. Activate autolytic enzymes. = Same as penicillin. Wider spectrum; Combine with clavulanic acid to protect against destruction by β-lactamase.
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Amoxicillin, ampicillin
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Extended-spectrum penicillin: H. influenzae H. pylori E. coli Listeria monocytogenes Proteus mirabilis Salmonella Shigella enterococci
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Amoxicillin, ampicillin
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Hypersensitivity reactions Rash Pseudomembranous colitis
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Amoxicillin, ampicillin
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Penicillinase in bacteria (a type of β-lactamase) cleaves β-lactam ring.
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Dicloxacillin, nafcillin, oxacillin
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Bactericidal penicillinase resistant because bulky R group blocks access of β-lactamase to β-lactam ring. Bind penicillin-binding proteins (transpeptidases). Block transpeptidase cross-linking of peptidoglycan in cell wall. Activate autolytic enzymes. = Same as penicillin. Narrow spectrum
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Dicloxacillin, nafcillin, oxacillin
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S. aureus (except MRSA; resistant because of altered penicillin-binding protein target site).
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Dicloxacillin, nafcillin, oxacillin
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Hypersensitivity reactions, interstitial nephritis.
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Piperacillin, ticarcillin
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Bactericidal Penicillinase sensitive Bind penicillin-binding proteins (transpeptidases). Block transpeptidase cross-linking of peptidoglycan in cell wall. Activate autolytic enzymes. Same as penicillin. Extended spectrum.
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Piperacillin, ticarcillin
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Pseudomonas spp. and gram-negative rods; susceptible to penicillinase; use with β-lactamase inhibitors.
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Piperacillin, ticarcillin
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Hypersensitivity reactions.
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Cephalosporins (generations I-V)
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Bactericidal Penicillinase sensitive β-lactam drugs that inhibit cell wall synthesis. Organisms typically not covered by cephalosporins are LAME: Listeria Atypicals (Chlamydia, Mycoplasma) MRSA Enterococci Exception: ceftaroline covers MRSA.
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Cephalosporins (generations I-V)
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Hypersensitivity reactions autoimmune hemolytic anemia disulfiram-like reaction vitamin K deficiency Exhibit cross-reactivity with penicillins. Incr. nephrotoxicity of aminoglycosides.
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Cephalosporins (generations I-V)
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Structural change in penicillin-binding proteins (transpeptidases).
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Cephalosporins, 1st generation
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cefazolin, cephalexin: PEcK.: gram-positive cocci Proteus mirabilis E. coli Klebsiella pneumoniae Cefazolin used prior to surgery to prevent S. aureus wound infections.
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Cephalosporins, 2nd generation
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cefoxitin, cefaclor, cefuroxime: HEN PEcKS. gram-positive cocci Haemophilus influenzae Enterobacter aerogenes Neisseria spp. Proteus mirabilis E. coli Klebsiella pneumoniae Serratia marcescens.
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Cephalosporins, 3rd generation
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ceftriaxone, cefotaxime, ceftazidime: serious gram-negative infections resistant to other β-lactams. Ceftriaxone - meningitis, gonorrhea, disseminated Lyme disease Ceftazidime - Pseudomonas.
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Cephalosporins, 4th generation
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cefepime: gram-negative organisms, with incr. activity against Pseudomonas and gram-positive organisms.
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Cephalosporins, 5th generation
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ceftaroline: broad gram-positive and gram-negative organism coverage, including MRSA; does not cover Pseudomonas.
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Carbapenems
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Imipenem, meropenem, ertapenem, doripenem.
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Carbapenems
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Imipenem is a broad-spectrum, β-lactamase-resistant carbapenem. Always administered with cilastatin (inhibitor of renal dehydropeptidase I) to decr. inactivation of drug in renal tubules.
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Carbapenems
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Gram-positive cocci Gram-negative rods Anaerobes. Wide spectrum, but significant side effects limit use to life-threatening infections or after other drugs have failed. Meropenem has a decr. risk of seizures and is stable to dehydropeptidase I.
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Carbapenems
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GI distress skin rash CNS toxicity (seizures) at high plasma levels.
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Monobactams
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Aztreonam
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Monobactams
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Less susceptible to β-lactamases. Prevents peptidoglycan cross-linking by binding to penicillin- binding protein 3. Synergistic with aminoglycosides. No cross-allergenicity with penicillins.
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Monobactams
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Gram-negative rods only - no activity against gram-positives or anaerobes. For penicillin-allergic patients and those with renal insufficiency who cannot tolerate aminoglycosides.
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Monobactams
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Usually nontoxic; occasional GI upset.
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30S inhibitors
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A = Aminoglycosides [bactericidal] T = Tetracyclines [bacteriostatic]
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50S inhibitors
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C = Chloramphenicol, Clindamycin [bacteriostatic] E = Erythromycin (macrolides) [bacteriostatic] L = Linezolid [variable] "Buy AT 30, CCEL (sell) at 50."
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Aminoglycosides
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Gentamicin Neomycin Amikacin Tobramycin Streptomycin. "Mean" (aminoglycoside) GNATS caNNOT kill anaerobes.
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Aminoglycosides
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Bactericidal irreversible inhibition of initiation complex through binding of the 30S subunit. Can cause misreading of mRNA. Also block translocation. Require O2 for uptake; therefore ineffective against anaerobes.
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Aminoglycosides
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Severe gram-negative rod infections. Synergistic with β-lactam antibiotics. Neomycin for bowel surgery.
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Aminoglycosides
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Nephrotoxicity Neuromuscular blockade Ototoxicity (especially when used with loop diuretics). Teratogen.
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Aminoglycosides
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Bacterial transferase enzymes inactivate the drug by acetylation, phosphorylation, or adenylation.
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Tetracyclines
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Tetracycline doxycycline minocycline
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Tetracyclines
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Bacteriostatic Bind to 30S and prevent attachment of aminoacyl-tRNA Limited CNS penetration. Doxycycline is fecally eliminated and can be used in patients with renal failure. Do not take tetracyclines with milk (Ca2+), antacids (Ca2+ or Mg2+), or iron-containing preparations because divalent cations inhibit drugs' absorption in the gut.
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Tetracyclines
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Borrelia burgdorferi M. pneumoniae Drugs' ability to accumulate intracellularly makes them very effective against Rickettsia and Chlamydia. Also used to treat acne.
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Tetracyclines
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GI distress Discoloration of teeth Inhibition of bone growth in children Photosensitivity Contraindicated in pregnancy
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Tetracyclines
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Decr. uptake or Incr. efflux out of bacterial cells by plasmid-encoded transport pumps.
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Chloramphenicol
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Bacteriostatic. Blocks peptidyltransferase at 50S ribosomal subunit.
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Chloramphenicol
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Meningitis (Haemophilus influenzae, Neisseria meningitidis, Streptococcus pneumoniae) Rocky Mountain spotted fever (Rickettsia rickettsii). Limited use owing to toxicities but often still used in developing countries because of low cost.
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Chloramphenicol
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Anemia (dose dependent) Aplastic anemia (dose independent) Gray baby syndrome (in premature infants because they lack liver UDP-glucuronyl transferase).
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Chloramphenicol
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Plasmid-encoded acetyltransferase inactivates the drug.
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Clindamycin
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Bacteriostatic. Blocks peptide transfer (translocation) at 50S ribosomal subunit.
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Clindamycin
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Anaerobic infections (e.g., Bacteroides spp., Clostridium perfringens) in aspiration pneumonia, lung abscesses, and oral infections. Also effective against invasive group A streptococcal infection.
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Clindamycin
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Pseudomembranous colitis (C. difficile overgrowth) fever diarrhea
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Oxazolidinones
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Linezolid
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Oxazolidinones
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Inhibit protein synthesis by binding to 50S subunit and preventing formation of the initiation complex.
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Oxazolidinones
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Gram-positive species including MRSA and VRE.
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Oxazolidinones
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Bone marrow suppression (especially thrombocytopenia) Peripheral neuropathy Serotonin syndrome
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Oxazolidinones
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Point mutation of ribosomal RNA
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Macrolides
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Azithromycin clarithromycin erythromycin
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Macrolides
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Bacteriostatic. Inhibit protein synthesis by blocking translocation ("macroslides"); bind to the 23S rRNA of the 50S ribosomal subunit.
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Macrolides
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Atypical pneumonias (Mycoplasma, Chlamydia, Legionella) STIs (Chlamydia) gram-positive cocci (streptococcal infections in patients allergic to penicillin) B. pertussis.
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Macrolides
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MACRO: Gastrointestinal Motility issues Arrhythmia caused by prolonged QT interval acute Cholestatic hepatitis Rash eOsinophilia. Increases serum concentration of theophyllines, oral anticoagulants. Clarithromycin and erythromycin inhibit cytochrome P-450.
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Macrolides
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Methylation of 23S rRNA-binding site prevents binding of drug.
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Trimethoprim
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Inhibits bacterial dihydrofolate reductase. Bacteriostatic.
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Trimethoprim
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Used in combination with sulfonamides (trimethoprim-sulfamethoxazole [TMP- SMX]), causing sequential block of folate synthesis. Combination used for UTIs Shigella Salmonella Pneumocystis jirovecii pneumonia treatment and prophylaxis toxoplasmosis prophylaxis.
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Trimethoprim
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Megaloblastic anemia leukopenia granulocytopenia. (May alleviate with supplemental folinic acid). TMP - Treats Marrow Poorly.
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Sulfonamides
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Sulfamethoxazole (SMX) sulfisoxazole sulfadiazine
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Sulfonamides
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Inhibit folate synthesis. Para-aminobenzoic acid (PABA) antimetabolites inhibit dihydropteroate synthase. Bacteriostatic (bactericidal when combined with trimethoprim). (Dapsone, used to treat lepromatous leprosy, is a closely related drug that also inhibits folate synthesis.)
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Sulfonamides
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Gram-positives gram-negatives Nocardia Chlamydia Triple sulfas or SMX for simple UTI.
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Sulfonamides
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Hypersensitivity reactions hemolysis if G6PD deficient nephrotoxicity (tubulointerstitial nephritis) photosensitivity kernicterus in infants displace other drugs from albumin (e.g., warfarin).
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Sulfonamides
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Altered enzyme (bacterial dihydropteroate synthase),decr. uptake, or incr. PABA synthesis.
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Fluoroquinolones
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Ciprofloxacin, norfloxacin, levofloxacin, ofloxacin, moxifloxacin, gemifloxacin, enoxacin.
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Fluoroquinolones
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Inhibit prokaryotic enzymes topoisomerase II (DNA gyrase) and topoisomerase IV. Bactericidal. Must not be taken with antacids.
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Fluoroquinolones
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Gram-negative rods of urinary and GI tracts (including Pseudomonas) Neisseria some gram-positive organisms.
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Fluoroquinolones
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GI upset superinfections skin rashes headache dizziness Less commonly, can cause leg cramps and myalgias. Contraindicated in pregnant women, nursing mothers, and children 60 years old and in patients taking prednisone.
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Fluoroquinolones
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Chromosome-encoded mutation in DNA gyrase, plasmid-mediated resistance, efflux pumps.
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Daptomycin
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Lipopeptide that disrupts cell membrane of gram-positive cocci.
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Daptomycin
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S. aureus skin infections (especially MRSA) bacteremia endocarditis VRE Not used for pneumonia (avidly binds to and is inactivated by surfactant).
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Daptomycin
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Myopathy rhabdomyolysis
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Metronidazole
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Bactericidal antiprotozoal Forms toxic free radical metabolites in the bacterial cell that damage DNA.
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Metronidazole
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Giardia Entamoeba Trichomonas Gardnerella vaginalis Anaerobes (Bacteroides, C. difficile). Used with a proton pump inhibitor and clarithromycin for "triple therapy" against H. Pylori.
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Metronidazole
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Disulfiram-like reaction (severe flushing, tachycardia, hypotension) with alcohol headache metallic taste
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M. tuberculosis, PROPHYLAXIS
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Isoniazid
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M. tuberculosis, TREATMENT
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Rifampin Isoniazid Pyrazinamide Ethambutol (RIPE for treatment)
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M. avium-intracellulare, PROPHYLAXIS
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Azithromycin rifabutin
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M. avium-intracellulare, TREATMENT
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More drug resistant than M. tuberculosis. Azithromycin or clarithromycin + ethambutol. Can add rifabutin or ciprofloxacin.
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M. leprae, TREATMENT
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Long-term treatment with dapsone and rifampin for tuberculoid form. Add clofazimine for lepromatous form.
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Inhibits MYCOLIC ACID SYNTHESIS
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Isoniazid
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Inhibits ARABINOGLYCAN SYNTHESIS (arabinosyl transferase)
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Ethambutol
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Inhibits mRNA SYNTHESIS (DNA-dependent RNA poylmerase)
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Rifabutin Rifampin
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Inhibits INTRACELLULAR (unclear mechanism)
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Pyrazinamide
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Rifamycins
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Rifampin rifabutin
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Rifamycins
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Inhibit DNA-dependent RNA polymerase.
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Rifamycins
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Mycobacterium tuberculosis; delay resistance to dapsone when used for leprosy. Meningococcal prophylaxis and chemoprophylaxis in contacts of children with Haemophilus influenzae type B.
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Rifamycins
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Minor hepatotoxicity and drug interactions ( Incr. cytochrome P-450); orange body fluids (nonhazardous side effect) Rifabutin favored over rifampin in patients with HIV infection due to less cytochrome P-450 stimulation. - Rifampin ramps up cytochrome P-450, but rifabutin does not.
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Rifamycins
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Mutations reduce drug binding to RNA polymerase. Monotherapy rapidly leads to resistance.
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Isoniazid
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Decr. synthesis of mycolic acids. Bacterial catalase-peroxidase (encoded by KatG) needed to convert INH to active metabolite.
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Isoniazid
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Mycobacterium tuberculosis. The only agent used as solo prophylaxis against TB.
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Isoniazid
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Neurotoxicity Hepatotoxicity Pyridoxine (vitamin B6) can prevent neurotoxicity.
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Isoniazid
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Mutations leading to underexpression of KatG.
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Pyrazinamide
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Mechanism uncertain. Pyrazinamide is a prodrug that is converted to the active compound pyrazinoic acid.
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Pyrazinamide
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Mycobacterium tuberculosis.
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Pyrazinamide
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Hyperuricemia Hepatotoxicity
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Ethambutol
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Decr. carbohydrate polymerization of mycobacterium cell wall by blocking arabinosyltransferase.
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Ethambutol
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Mycobacterium tuberculosis.
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Ethambutol
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Optic neuropathy (red-green color blindness). Pronounce "eyethambutol."
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Antimicrobial prophylaxis, High risk for endocarditis and undergoing surgical or dental procedures
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Amoxicillin
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Antimicrobial prophylaxis, Exposure to gonorrhea
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Ceftriaxone
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Antimicrobial prophylaxis, History of recurrent UTIs
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TMP-SMX
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Antimicrobial prophylaxis, Exposure to meningococcal infection
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Ceftriaxone, ciprofloxacin, or rifampin
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Antimicrobial prophylaxis, Pregnant woman carrying group B strep
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Penicillin G
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Antimicrobial prophylaxis, Prevention of gonococcal conjunctivitis in newborn
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Erythromycin ointment
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Antimicrobial prophylaxis, Prevention of postsurgical infection due to S. aureus
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Cefazolin
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Antimicrobial prophylaxis, Prophylaxis of strep pharyngitis in child with prior rheumatic fever
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Benzathine penicillin G or oral penicillin V
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Antimicrobial prophylaxis, Exposure to syphilis
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Benzathine penicillin G
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Prophylaxis in HIV patients, CD4 < 200 cells/mm3
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TMP-SMX: Pneumocystis pneumonia
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Prophylaxis in HIV patients, CD4 < 100 cells/mm3
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TMP-SMX: Pneumocystis pneumonia and toxoplasmosis
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Prophylaxis in HIV patients, CD4 < 50 cells/mm3
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Azithromycin or clarithromycin: Mycobacterium avium complex
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Treatment of MRSA
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vancomycin daptomycin linezolid tigecycline ceftaroline
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Treatment of VRE
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linezolid and streptogramins (quinupristin, dalfopristin).
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Treatment of Multidrug-resistant P. aeruginosa, multidrug-resistant Acinetobacter baumannii:
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polymyxins B and E (colistin)
