Antibiotics

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Author:
manjinder
ID:
152858
Filename:
Antibiotics
Updated:
2012-05-08 01:14:13
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Pharm
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Description:
antimicrobial drugs
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  1. block cell wall synthesis by inhibition of peptidoglycan cross-linking
    • penicillins, methicillin, ampicillin, piperacillin, cephalosporins, imipenem/meropenem, aztreonam
    • bactericidal
  2. block peptidoglycan synthesis
    • bacitracin, vancomycin
    • bactericidal
  3. inhibit bacterial protein synthesis at 30S ribosomal subunit
    • aminoglycosides: bactericidal; have synergistic effect w/ penicillins
    • tetracyclines: bacteriostatic: have antagonistic effect w/ penicillins
  4. Block protein synthesis at 50s ribosomal subunit
    • chloramphenicol, macrolides, clindamycin, streptogramins (quinupristin, dalfopristin), linezolid
    • bacteriostatic
  5. block nucleotide synthesis
    • sulfonamides, trimethoprim
    • bacteriocidal
  6. inhibit DNA topoisomerases
    • fluoroquinolones
    • bacteriocidal
  7. block mRNA synthesis
    • rifampin
    • bactericidal
  8. DNA damage
    • metronidazole
    • bacteriocidal
  9. Penicillins
    • Mechanism: binds to penicillin-binding proteins leading to block of transpeptidase cross-linking of peptidoglycan and activate autolytic enzymes
    • Resistance: pencillinases- break the lactam ring; structural change in PBP leads to MRSA; gram -s such as Pseudomonas can change porin structure.
    • Use: Penicillin G and V (b-lactamase sensitive)--> Syphilis
    • Methicillin, nafcillin, oxacillins (b-lactamase resistant) --> S. aureus but lead to MRSA
    • Amoxillin and ampicillin (b-lactamase sensitive) --> gram + cocci (not staph), Listeria, Gram - (E. coli, influenzae, H. pylori), Borrelia
    • Ticarcillin, piperacillin, azlocillin, carbenicillin (b-lactamase sensitive) --> antipseudomonal
    • Clavulanic acid, sulbactam, tazobactam (b-lactamase inhibitors)
    • Side Effect: hypersensitivity, GI distress (especially ampicillin), Jarisch-Herxheimer reaction in treatment of syphilis
    • eliminated via active tubular secretion except nafcillin and oxacillin which are eliminated in biles
  10. Cephalosporins
    • Mechanism: binds to penicillin-binding proteins leading to block of transpeptidase cross-linking of peptidoglycan and activate autolytic enzymes
    • Resistance: pencillinases- break the lactam ring; structural change in PBP leads to MRSA; gram -s such as Pseudomonas can change porin structure.
    • 1st generation: cefazolin, cephalexin --> sugical prophylaxis, gram + cocci and E.coli, Proteus mirabilis, Klebsiella pneumoniae
    • 2nd generation: cefotetan, cefaclor, cefuroxime (crosses BBB) better gram - coverage.
    • 3rd generation: ceftriaxone, cefotaxime, ceftazidime --> empirical management of sepsis and meningitis. No activity against LAME: Listeria, Atypicals (chlamydia, mycoplasma), MRSA, enterococci
    • 4th generation: cefepime: IV, increased activity against Pseudomonas and gram + organisms
    • Side effects: hypersensitivity; use macrolides or aztreonam in case of allergies to lactams; disulfiram-like effect
    • Renal clearance except cefoperazone, and ceftriaxone eliminated in bile
  11. Imipenem and Meropenem
    • Mechanism: binds to penicillin-binding proteins leading to block of transpeptidase cross-linking of peptidoglycan and activate autolytic enzymes
    • Use: in hospital agents for empiric use in severe life-threatening infections for gram - and +
    • Imipenem given w/ cilastatin to inhibit renal elimination
    • Side effects: GI distress, CNS effects (seizures w/ imipenem)
  12. Aztreonam
    • Mechanism: binds to penicillin-binding proteins3 leading to block of transpeptidase cross-linking of peptidoglycan and activate autolytic enzymes
    • Use: IV drug ONLY active against gram - RODS; no cross-allergenicity w/ penicillins or cephalosporins; and for those who can't tolerate aminoglycosides
  13. Vancomycin
    • Mechanism: binding at D-ala-D-ala muramyl pentapeptide to sterically hinder the transglycosylation reactions involved in elongation of peptidoglycan chains; doesn't interfere w/ PBPs
    • Use: gram positive only: MRSA, enterococci, Clostridium difficule- oral (Metronidazole is DOC)
    • used IV, doesn't enter CNS, eliminated by renal filtration
    • resistance: terminal D-ala is replaced by D-lactate
    • Toxicity: Nephrotoxicity, ototoxicity, thrombophlebitis, diffuse flushing- "red man syndrome" (can largelly prevent by pretreatment w/ antihistamines and slow infusion rate)
  14. Aminoglycosides (30S)
    Linezolid (50S) used for VRSA, VRE causes BMS
    • Gentamicin, Neomycin, Amikacin, Tobramycin, Streptomycin
    • Mechanism: inhibit formation of initiation complex (on P site) and Aminoglycosides also cause misreading of mRNA (making them bactericidal)
    • Req O2 for uptake
    • Use: gram - rod. Synergistic w/ b-lactam antibiotics. Streptomycin for TB and DOC for bubonic plague and tularemia
    • Toxicity: Nephrotoxicity, ototoxicity, teratogen, neuromuscular blockade (dec ACh release), contact dermatitis (neomycin- used topicially)
    • Resistance: acetylation, phosphorylation, adenylation- makes it more water soluble
  15. Tetracyclines (30S)
    • Doxycycline, demeclocycline (used for SIADH), minocycline
    • Mechanism: binds to 30S and prevent attachment of aminoacyl-tRNA to A site. Limited CNS penetration.
    • Use: Borrelia burgdorferi, M pneumoniae. Drug's ability to accumulate intracellularly makes it very effective against Rickettsia and Chlamydia. Doxycycline is fecally eliminated and can be used in patients w/ renal failure.
    • Must NOT take w/ milk, antacids, or iron containing preparations
    • Toxicity: GI distress, discoloration of teeth and inhibition of bone growth in children, photosensitivity.
    • Contraindicated in pregnancy
    • Resistance: dec uptake into cells or inc efflux out of cell by plasmid-encoded trasport pumps (Pglycoside Pumps)
  16. Chloramphenicol (lipid soluble)
    • Mechanism: blocks peptide bond formation at 50S ribosomal subunit
    • Use: Meningitis, sepsis
    • Toxicity: Anemia, aplastic anemia, gray baby syndrome because of lack of liver UDP-glucuronyl transferase
    • Resistance: plasmid-encoded acetyltransferase that inactivates drug
  17. Clindamycin
    • Mechanism: inhibit translocation of peptidyl-tRNA from A site to P site
    • Use: Anaerobic infection, gram +, treat anaerobes above the diaphragm vs metronidazole below; concentration in bone has clinical value in osteomyelitis
    • Toxicity: GI distress, fever, diarrhea
  18. Macrolides
    • Erythromycin, azithromycin, clarithromycin
    • Mechanism: inhibit protein synthesis by blocking translocation; bind to 23S rRNA of the 50S ribosomal subunit
    • Use: Atypical pneumonias (mycoplasma, chlamydia, legionella), URI, STD, allergic to penicillin, Neisseria
    • Toxicity: prolonged QT interval, GI discomfort- stimulate motilin receptors, acute cholestatic hepatitis, eosinophilia, skin rashes, cause reversible deafness at high doses
    • Resistance: methylation of 23S rRNA binding site
  19. Sulfonamides
    • Sulfamethoxazole (SMX), sulfisoxazole, sulfadiazine
    • Mechanism: PABA antimetabolites inhibit dihydropteroate synthetase
    • Use: +, -, Nocardia, Chlamydia
    • Toxicity: hypersensitivity (Stevens Johnson syndrome), nephrotoxicity (causes kidney stones), photosensitivity, kernicterus in infants (because displaces bilirubin from albumin)
    • Resistance: altered enzyme, dec uptake, inc PABA synthesis
  20. Trimethoprim, pyrimethamine
    • Mechanism: Inhibits bacterial dihydrofolate reductase
    • Use: TMP-SMX used for UTI, shigella, salmonella, pneumocystis jiroveci pneumonia prophylaxis in HIV
    • Pyrimethamine-SMX: prophylaxis and Rx for T. gondii
    • Toxicity: megaloblastic anemia, leukopenia, granulocytopenia alleviated w/ folinic acid (leucovorin)
  21. Fluoroquinolones
    • Ciprofloxacin, norfloxacin, levofloxacin, ofloxacin, sparfloxacin, moxifloxacin, gatifloxacin, enoxacin, nalidixic acid (quinolone)
    • Mech: inhibit DNA gyrase (topoisomerase II and IV); therefore leads to + supercoil
    • Use: - rods for urinary and GI tracts (traveler's diarrhea), Neisseria, chlamydia, gonorrhea, must not be taken w/ antacids (Fe, Ca limit their absorption)
    • Toxicity: GI upset, superinfections, phototoxicity, skin rashes, headache, dizziness, tendonitis in adults, leg cramps and myalgias in kids, all quinolones inc QT interval
    • contraindicated in pregnant women and children
  22. Metronidazole
    • Mech: forms free radical toxic metabolites in the bacterial cell that damage DNA.
    • Use: Giardia, Entamoba, Trichomonas, Gardnerella vaginalis, Anaerobes (C. difficile). Used w/ bismuth and amoxicillin (or tetracycline) for H Pylori
    • Toxicity: Disulfiram-like reaction w/ alcohol, headache, metallic taste
  23. M. tuterculosis, M. avium intracellulare, M. leprae Prophylaxis and Rx
    • TB: Prophylaxis- isoniazid, Rx: rifampin, isoniazid, pyrazinamide, ethambutol
    • M. avium: prophylaxis- azithromycin, Rx: azithromycin, rifampin, ethambutol, streptomycin
    • M. leprae: Rx dapsone, rifampin, clofazimin
  24. Isoniazid (INH)
    • dec synthesis of mycolic acids. bacteria catalase peroxidase (KatG) needed to convert INH to active metabolite
    • Use: mycobacterium tuberculosis
    • Toxicity: neurotoxicity, hepatotoxicity, lupus. Pyridoxine (B6) can prevent neurotoxicity, and lupus
  25. Rifampin
    • inhibits DNA- dependent RNA polymerase (nucleic acid synthesis inhibitor)
    • Use: TB, delays resistance to dapsone when used for leprosy. used for meningococcal prophylaxis and chemoprophylaxis in contacts of children w/ H. influenzae type B
    • Toxicity: hepatotoxicity
    • 4 R's
    • RNA polymerase inhibitor
    • Revs up microsomal P-450
    • Red/orange body fluids
    • Rapid resistance if used alone
  26. Ethambutol
    • dec carbohydrate polymerization of mycobacterium cell wall by blocking arabinosyltransferase
    • Use: TB
    • Toxicity: optic neuropathy (red-green color blindness)
  27. Pyrazinamide
    • inhibits mycolic acid production, effective in acidic pH of phagolysosomes where TB engulfed by macrophages is found
    • Use: TB
    • Toxicity: hyperuricemia, hepatoxicity
  28. Prophylaxis
    1 Meningococcal infection
    2 gonorrhea
    3 syphilis
    4 history of recurrent UTI
    5 Endocarditis w/ surgical or dental procedures
    • 1 ciprofloxacin (DOC), rifampin, minocycline
    • 2 ceftriaxone
    • 3 penicillin G
    • 4 TMP-SMX
    • 5 penicilins
  29. VRE rx
    linzolid and streptogramins (quinupristin/dalfopristin)
  30. community-acquired peumonia:
    1. outpatient
    2. inpatient
    3. ICU
    • Macrolides
    • Fluoroquinolones
    • b-lactam + (fluoroquinolone or azithromycin)

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