Antimicrobials Flashcards
(51 cards)
Empiric antimicrobial therapy
Use of antimicrobial agents before the pathogen responsible for an illness has been identified, used in cases where there is a significant risk of morbidity if a therapy is withheld until specific pathogen is detected
Steps in empiric therapy
Formulate clinical diagnosis of microbial infection, obtain specimens for lab, formulate microbiologic diagnosis, determine necessity for empiric therapy, institute treatment
Selective toxicity
The ability of a drug to injure a target cell or organism without injuring other cells or organisms that should not be injured
Methods of selective toxicity
Unique target must be present in pathogen but absent in the host OR target must be structurally different in the pathogen than in the host OR target must be more important in the pathogen than in the host
Things to consider in the selection of antibiotics
Identity and sensitivity of the organism, site of infection, safety of the agent, patient factors, the cost of therapy
Narrow spectrum antibiotics
Gram positive cocci and gram negative bacilli, gram negative aerobes, Mycobacterium tuberculosis
Gram positive cocci and gram negative bacilli
Narrow spectrum- penicillin G and V, penicillinase-resistant penicillins (nafcillin methicillin), vancomycin, erythromycin, clindamycin
Gram negative aerobes
Narrow spectrum- aminoglycosides (gentamicin), cephalosporins (2nd generation)
Mycobacterium tuberculosis
Isoniazid, rifampin, ethambutol, pyrazinamide
Broad spectrum antibiotics
Gram positive and negative organisms
Gram positive and negative organisms
Broad spectrum- broad spectrum penicillins (ampicillin), extended-spectrum penicillins (carbenicillin), cephalosporins (3rd generation), tetracyclines, imipenem, trimethoprim, sulfonamides (sulfamethoxazole), fluoroquinolones (ciprofloxacin, norfloacin)
Disruption of bacterial cell wall
Without cell walls, bacteria absorb water, swell, and burst, several families of drugs act to weaken cell wall and promote lysis of the bacteria, mammalian cells have no cell wall
Disruption of bacterial protein synthesis
Synthesis of proteins employs ribosomes, target bacterial ribosomes
Inhibition of enzymes unique to bacteria
Sulfonamides inhibit bacterial enzyme required for folic acid synthesis, bacteria cannot take up folic acid from environment, mammals do not synthesize folic acid, making it selective
Inhibition of nucleic acid
DNA gyrase
Inhibition of membrane function
Fungal membranes
Minimal inhibitory concentration (MIC)
Minimal concentration where the antimicrobial can inhibit bacterial growth
Minimal bactericidal concentration (MBC)
Minimal concentration where the antimicrobial kills bacteria
Things that determine an anti-microbial’s effectiveness against an organism
Antibiotic must bind to its target site in the bacterium, drug most occupy an adequate number of binding sites related to its concentration within the microorganism, antibiotic should remain at the binding site for a sufficient period of time to cause sufficient inhibition
Factors that may cause resistance to antibiotics
Failure of drug to reach its target, drug inactivation, target alteration
Failure of drug to reach its target
Outer membrane of a gram negative bacteria is a barrier that excludes large polar molecules from entering the cell, small polar molecules enter through porins
Mutations of porin
Can cause loss or blockage of a porin that the antibiotic used to gain access to the cell
Mutations inhibiting transport mechanisms
Can confer resistance to a drug with an intracellular target that requires active transport across the cell membrane (gentamicin)
Drug inactivation
Bacterial resistance may result from the production of enzymes that modify or destroy the antibiotic
