14-15 Selecting Anti-Microbials Flashcards
5 Steps to Approach Empiric Therapy
1- Clinical Diagnosis 2- Obtain Specimens 3- Microbiologic Diagnosis 4- Determine necessity for empiric therapy (is the pt at high risk) 5- Institute treatment
5 things to consider in selecting antibiotics
1- ID/sensitivity 2- Site of infection 3- Safety of agent 4- Pt health factors 5- cost of therapy
use of antimicrobial agents before the pathogen for a particular illness is known
Empiric Therapy
Combination (Empiric) Therapy Drugs
Clindamycin + gentamicin
Single broad spectrum antibiotic
Imipenem / cilastatin
3 ways to distinguish target from host
1- Cell Wall
2- Ribosomes/Protein Synthesis
3- Enzyme action
family that inhibits the synthesis of the peptidoglycan layer
Beta-Lactams
Examples of Beta Lactams
Cephalosporin, Penicillin, bacitracin, fosfomycin, vancomycin
Competes with PABA to decrease the action of an enzyme that makes folic acid from PABA (Inhibits PABA–> Dihydrofolic Acid)
Sulphonamides
Inhibits dihydrofolate reductase (Dihydrofolic Acid FH4)
Trimethoprim
RNA polymerase inhibitor
Rifampin
DNA gyrase inhibitor
Fluoroquinolones
Aminoglycosides, Chloramphenicol, Clindamycin, Macrolides, Streptogramins, Tetracycline
Protein synthesis inhibitors
What bacteria do you use the following on: Penicillin G and V, Penicillinase-resistant penicillins: nafcillin, methicillin, Vancomycin, Erythromycin , Clindamycin
Gram-positive cocci and gram-negative bacilli
What bacteria do you use the following on: Aminoglycosides (e.g., gentamicin), Cephalosporins (e.g., 2nd generation)
Gram-negative aerobes
What bacteria do you use the following on:Broad-spectrum penicillins such as ampicillin, Extended-spectrum penicillins such as carbenicillin, Cephalosporins (third generation), Tetracyclines, Imipenem, Trimethoprim, Sulfonamides: sulfamethoxazole, Fluoroquinolones: ciprofloxacin, norfloxacin
Gram-positive & negative microorganisms
When the drug is > MIC it
Inhibits bacterial growth
When the drug is >MBC it
kills the organism
3 Mechanisms for why a drug would not reach its target
1- Gram (-) outer membrane porins
2- Target is intracellular
3- Efflux Pumps
2 Examples of Drug Inactivation
1- Bacteria producing beta-lactamases
2- Mycobacterium tuberculosis losing the ability to convert isoniazid to its active form
What type of antibiotics promote resistance and how?
Broad spectrum antibiotics, kills off normal flora which are competing organisms to the infection
A drug that targets the ribosome and is actively transported across the cell membrane using the cell’s electrochemical gradient
Gentamicin
Give 3 Antibiotic Classes Affected by Efflux Pumps
Tetracyclines, chloramphenicol, fluoroquinolones, macrolides, beta-lactam antibiotics
A new infection that develops because the antibiotics eliminated the inhibitory influence of the normal flora thus allowing for a second infectious agent to flourish
Superinfection
3 qualities of a drug of choice
Increased efficacy, decreased toxicity, and narrow spectrum
3 conditions that contraindicate a primary drug
1- Allergic
2- Drug is unable to penetrate to the infection
3- Pt has unusual susceptibility to drug, more toxic
When should sulphonamides not be used, why?
In infants, it would produce kernicterus which causes a severe displacement of bilirubin from plasma proteins, resulting in a severe neurologic disorder
binds to developing teeth causing discoloration, targets protein synthesis
Tetracycline
In what infection does the use of combination antibiotics actually decrease the chance of resistance
tuberculosis
In fungal meningitis, what can you give the pt along with amphotericin B to prevent the drug from damaging the kidneys
flucytosine
In treatment of ________ , ______ can be given along with aminoglycosides to increase the drugs uptake
Enterococcal endocarditis, penicillin
What characteristic implies that two drugs are synergistic
a 4 fold increase in the antibacterial activity of one of the drugs, a decrease to 1/4 the MIC for that drug
3 Mechanisms for antibiotic synergism and an example for each
1- Blockade of steps in metabolism (Trimethoprim-sulfamethoxazole for folic acid production )
2- Inhibition of enzymatic activity (Beta-lactams and beta-lactamase inhibitor like sublactam)
3- Enhancement of Ab uptake (Penicillins increase uptake of aminoglycosides in staphylococci, enterococci)
2 Examples of Antibiotic Antagonism
1-Chloramphenicol is stopping protein synthesis then penicillin doesn’t work
2- Tetracycline inhibits the growth of the bacteria and thus stops penicillin
Ends in cillin
Penicillins, bind to PBP
Ends in cycline
Tetracycline, binds 30s ribosomal subunit
Ends in mycin or micin
Aminoglycosides, inhibits protein synthesis
Ends in oxacin
Quinolone, DNA gyrase inhibitor
Starts with cef or ceph
cephalosporins, inhibits protein sysnthesis
ends in micin
Macrolides, inhibits protein synthesis (similar to aminoglycosides)
What type of agent shows stopped growth over time
Bacteriostatic
What type of agent shows declining growth over time
Bactericidal
3 Examples of bactericidal drugs
Beta lactams, rifampin, and quinolones
3 examples of bacteriostatic drugs
Tetracyclines, chloramphenicol, macrolides
