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1、Anti infective agents,Chapters 37,38,39 & 41,Antibiotics: Definition,Medications used to treat bacterial infections Ideally, before beginning antibiotic therapy, the suspected areas of infection should be cultured to identify the causative organism and potential antibiotic susceptibilities,Antibioti
2、cs: Classes,SulfonamidesPenicillins CephalosporinsTetracyclinesMacrolides,Aminoglycosides Quinolones,Figure 37-1 Bacterial morphologies. (From Murray, P.R., Rosenthal, K.S., Kobayashi, G.S., & Pfaller, M.A. (2002). Medical microbiology. St. Louis, MO: Mosby.),Figure 37-3 Gram-stain morphology of bac
3、teria. The crystal violet of Gram stain is precipitated by Gram iodine and is trapped in the thick peptidoglycan layer in gram-positive bacteria. The decolorizer disperses the gram-negative outer membrane and washes the crystal violet from the thin layer of peptidoglycan. Gram-negative bacteria are
4、visualized by the red counterstain. (From Murray, P.R., Rosenthal, K.S., Kobayashi, G.S., & Pfaller, M.A. (2002). Medical microbiology. St. Louis, MO: Mosby.),Figure 37-4 Gram-positive and gram-negative bacteria. A gram-positive bacterium has a thick layer of peptidoglycan (left). A gram-negative ba
5、cterium has a thin peptidoglycan layer and an outer membrane (right). Structures in parentheses are not found in all bacteria. (From Murray, P.R., Rosenthal, K.S., Kobayashi, G.S., & Pfaller, M.A. (2002). Medical microbiology. St. Louis, MO: Mosby.),Antibiotic Therapy,Empiric therapy: treatment of a
6、n infection before specific culture information has been reported or obtained Prophylactic therapy: treatment with antibiotics to prevent an infection, as in intraabdominal surgery,Antibiotic Therapy (contd),Therapeutic response Decrease in specific signs and symptoms of infection are noted (fever,
7、elevated WBC, redness, inflammation, drainage, pain) Subtherapeutic response Signs and symptoms of infection do not improve,Antibiotic Therapy (contd),Four common mechanisms of action Interference with cell wall synthesis Interference with protein synthesis Interference with DNA replication Acting a
8、s a metabolite to disrupt critical metabolic reactions inside the bacterial cell,Actions of Antibiotics,Bactericidal: kill bacteria Bacteriostatic: inhibit growth of susceptible bacteria, rather than killing them immediately; will eventually lead to bacterial death,Antibiotics: Sulfonamides,One of t
9、he first groups of antibiotics sulfadiazine Sulfamethoxazole (Bactrim) sulfisoxazole,Sulfonamides: Mechanism of Action,Bacteriostatic action Prevent synthesis of folic acid required for synthesis of purines and nucleic acid Do not affect human cells or certain bacteriathey can use preformed folic ac
10、id,Sulfonamides: Indications,Treatment of UTIs caused by susceptible strains of: Enterobacter spp., Escherichia coli, Klebsiella spp., Proteus mirabilis, Proteus vulgaris, Staphylococcus aureus Nocardiosis Pneumocystis carinii pneumonia (PCP) Upper respiratory tract infections Other uses,Sulfonamide
11、s: Combination Products,trimethoprim/sulfamethoxazole Used to treat UTIs, PCP, otitis media, other conditions erythromycin/sulfisoxazole Used to treat otitis media sulfisoxazole Used to treat otitis media, UTIs, other conditions,Beta-Lactam Antibiotics,Penicillins Cephalosporins Carbapenems Monobact
12、ams,Penicillins,Natural penicillins Penicillinase-resistant penicillins Aminopenicillins Extended-spectrum penicillins,Penicillins (contd),Natural penicillins penicillin G, penicillin V potassium Penicillinase-resistant penicillins Cloxacillin Aminopenicillins amoxicillin, ampicillin, pivamicillin A
13、nti-pseudomonal penicillins piperacillin sodium,Penicillins (contd),First introduced in the 1940s Bactericidal: inhibit cell wall synthesis Kill a wide variety of bacteria Also called “beta-lactams”,Penicillins (contd),Bacteria produce enzymes capable of destroying penicillins These enzymes are know
14、n as beta-lactamases As a result, the medication is not effective,Penicillins (contd),Chemicals have been developed to inhibit these enzymes: Clavulanic acid (Clavulin) Tazobactam Sulbactam These chemicals bind with beta-lactamase and prevent the enzyme from breaking down the penicillin,Penicillins:
15、 Mechanism of Action,Penicillins enter the bacteria via the cell wall Inside the cell they bind to penicillin-binding protein Once bound, normal cell wall synthesis is disrupted Result: bacteria cells die from cell lysis Penicillins do not kill other cells in the body,Penicillins: Indications,Preven
16、tion and treatment of infections caused by susceptible bacteria, such as: Gram-positive bacteria Streptococcus, Enterococcus, Staphylococcus spp.,Penicillins: Adverse Effects,Allergic reactions occur in 0.7% to 8% of cases Urticaria, pruritus, angioedema 10% of allergic reactions are life threatening 10% of these are fatal,Penicillins: Side Effects,Common side effects Nausea, vomiting, diarrhea, abdominal pain Other side effects are less common,Cephalosporins,First generation Second generation Third generation Fourth generation,
