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CHAPTER 41

CHAPTER 41. Antibacterial Agents. Bacterial Morphology. Bacteria are classified by bacterial shape and colony arrangement Cocci are spherical in shape and usually arranged in pairs (diplo), chains (strepto), or clusters (staphylo) Bacilli are rod-like in shape

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CHAPTER 41

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  1. CHAPTER 41 Antibacterial Agents

  2. Bacterial Morphology • Bacteria are classified by bacterial shape and colony arrangement • Cocci are spherical in shape and usually arranged in pairs (diplo), chains (strepto), or clusters (staphylo) • Bacilli are rod-like in shape • Spirilla are curved and rod-like in shape • See P 496

  3. Gram Staining • Gram staining classification is based on ability of the bacterial membrane to stain either red or blue • Bacteria that take up the red stain are classified as gram positive, Gm(+) • Bacteria that take up the blue stain are classified as gram negative, Gm(-) • Gm(-) bacteria have an additional outer lipopolysaccharide membrane layer (endotoxin) that is toxic and that can produce endotoxic shock

  4. Antibacterial Chemotherapy • Defined as the use of drugs to kill or inhibit the growth of infectious bacteria • Bactericidal drugs kill the bacteria • Bacteriostatic drugs inhibit the growth of bacteria and body defenses and immune mechanisms are required to rid the body of infecting bacteria

  5. Antibacterial Spectrum • Refers to the range of bacteria that are killed or inhibited by any antibacterial drug • Narrow spectrum drugs are effective against a limited number of different bacterial species • Broad spectrum drugs are effective against a wide range of different bacterial species

  6. Bacterial Resistance • Bacteria have the ability to produce proteins that help them resist antimicrobial drug actions • Some bacteria produce beta-lactamase enzymes that inactivate penicillins and cephalosporins • Some bacteria produce proteins that prevent drugs from penetrating the bacterial membrane or proteins that remove the drugs once they have passed through the bacterial membrane • When bacterial resistance occurs other drugs must be used to treat the infection

  7. Six families of antibacterial drugs • 1. penicillins • 2. cephalosporins • 3. tetracyclines • 4. aminoglycosides • 5. macrolides • 6. fluoroquinolones • 7. other

  8. Penicillins • Bacteriocidal drugs that inhibit cell wall synthesis • 1st generation drugs have a narrow spectrum and indicated mostly for Gm(+) infections • 2nd generation drugs have a wider spectrum that includes most common Gm(+) / Gm(-) bacterial infections • 3rd and 4th generation drugs have a broad spectrum and are effective against most Gm(-) bacteria

  9. Penicillins • 1st generation • Penicillin G - IM, IV • Penicillin V – PO • 2nd generation • Methicillin (Staphcillin) • 3rd generation • Carbenicillin (Geocillin) • 4th generation • Piperacillin (Pipracil)

  10. Cephalosporins • Bacteriocidal drugs that inhibit cell wall synthesis • 1st generation drugs are effective against most common Gm(+) and Gm(-) bacteria • 2nd, 3rd, and 4th generation cephalosporins have increasing activity against Gm(-) bacteria • Cephalosporins are the drugs of choice for infections caused by Klebsiella pneumoniae • Cephalosporins are more resistant to inactivating beta-lactamase enzymes than penicillins

  11. Cephalosporins • 1st generation • Cephalexin (Keflex) – PO • 2nd generation • Cefaclor (Ceclor) – PO • 3rd generation • Ceftriaxone (Rocephin) – IM,IV • 4th generation • Cefepime (Maxipime) – IM,IV

  12. Adverse Effects Common to Penicillins and Cephalosporins • Minor GI disturbances and diarrhea • Hypersensitivity or allergic reactions that include delayed skin reactions or immediate anaphylactic reactions • Higher dosages may cause bleeding problems • Higher dosages may cause CNS disturbances and possible seizures

  13. Aminoglycosides • Classified as broad spectrum antibiotics • Bacteriocidal drugs that inhibit bacterial protein synthesis • Administered IM or IV for systemic effects • Usually the drugs of choice for serious gram negative infections • Nephrotoxicity and ototoxicity are the most serious adverse effects

  14. Aminoglycosides • Gentamicin (Garamycin) • Kanamycin (Kantrex) • Streptomycin • IM or IV only • Often used in combination therapy

  15. Tetracyclines • Basteriostatic drugs that inhibit bacterial protein synthesis • Administered orally, but not with dairy or antacid products • Doxycycline (Vibramycin) is the most widely used tetracycline and usually taken once per day • Adverse effects include GI disturbances, rash, and photosensitivity • Tetracyclines are contraindicated during pregnancy, nursing, and in children < age 8

  16. Sulfonamides • Bacteriostatic drugs that inhibit bacterial folic acid synthesis • Sulfonamides (Gantricin) are mainly indicated for treatment of urinary tract infections • Trimethoprim/sulfamethoxazole (Bactrim, Septra) has a broad antibacterial spectrum and many indications • Adverse effects include rash, allergy, blood disorders, and renal tubule damage

  17. Macrolide Antibiotics • Bacteriostatic drugs that inhibit bacterial protein synthesis, effective with oral administration • Erythromycin often used in penicillin allergic patients for minor ear and throat infections • Azithromycin (Zithromax) and clarithromycin (Biaxin)have a broader antibacterial spectrum and clinical uses • Adverse effects include heartburn, rashes, and GI disturbances

  18. Fluroquinolones • Bactericidal drugs that inhibit an enzyme essential to the function of bacterial DNA • Administered orally • Indicated for a wide variety of urinary, soft tissue, bone, and respiratory infections • Adverse effects include GI disturbances, rash, photosensitivity, and joint pain • Contraindicated in pregnancy and young children

  19. Fluroquinolones • Ciprofloxacin (Cipro) • Levofloxacin (Levaquin) • Given PO - often used for throat infection& pneumonea • May cause tendon rupture

  20. Miscellaneous Antimicrobials • Chloramphenicol (Chloromycetin) is reserved for serious infections such as typhoid fever and meningitis • Clindamycin (Cleocin) indicated for Gm(+) and anaerobic infections – may cause C dif colitis • Vancomycin indicated for resistant Gm(+) staphylococcal infections (MERSA) • Quinupristin-dalfopristin and linezolid indicated for Gm(+) infections resistant to vancomycin – rarely used

  21. Drugs Used to Treat Tuberculosis • Tuberculosis requires prolonged treatment with multiple drugs, usually 3 or 4 different drugs • The first line drug regimen includes isoniazid, rifampin, pyrazinamide, and ethambutol • After 2–4 months of treatment ethambutol and pyrazinamide are usually eliminated • Isoniazid and rifampin therapy is continued for 6–12 months • Drug resistance is a major problem

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