Antimicrobial Chemotherapy Flashcards
Define bactericidal
An antimicrobial that kills bacteria (e.g. the penicillin
Define bacteriostatic
An antimicrobial that inhibits growth of bacteria (e.g. erythromycin).
Define a sensitive organism
An organism is considered sensitive if it is inhibited or killed by levels of the antimicrobial that are available at the site of infection
Define a resistant organisms
An organism is considered resistant if it is not killed or inhibited by levels of the antimicrobial that are available at the site of infection.
Define MIC
Minimal inhibitory concentration is de ned as the minimum concentration of antimicrobial needed to inhibit visible growth of a given organism.
Define MBC
Minimal bactericidal concentration is de ned as the minimum concentration of the antimicrobial needed to kill a given organism.
Describe some routes of drug administration
Topical - to surface e.g. king
Systemic - internal, either oral or parenterally
Parenteral - IV, intramuscularly, subcutaneously
What are the three main mechanisms of action of antibiotics?
Inhibit cell wall synthesis e.g. penicillins and cephalosporins, glycopeptides (vancomycin and teicoplanin)
Inhibit nucleic acid synthesis e.g. trimethoprim and ciproflaxacin
Inhibit protein synthesis e.g. gentamicin and erythromycin
Why don’t penicillins and cephalosporins (Beta-lactams) affect human cells?
These antibiotics disrupt peptidoglycan synthesis, and PG is not found in human cells.
Describe the action of penicillins and cephalosporins
Both are beta-lactam antibiotics, which inhibit peptidoglycan synthesis by binding the enzymes responsible for cross-linking carbohydrate chains, the penicillin binding proteins (PBPs). Cells are then killed by autolytic enzymes. Inhibit cell wall synthesis!
What are glycopeptides and what is their antimicrobial action?
Examples include vancomycin and teicoplanin, and this group of drugs inhibit cell wall synthesis. Also inhibit cell wall synthesis, though inhibit a stage earlier than beta-lactam antibiotics. Only act on gram positive organism as they can not penetrate the gram negative cell wall. Given parenterally though they are not absorbed in the GI tract. Vancomycin is toxic, monitor serum levels.
Define the antimicrobial effect of aminoglycosides
Example is gentamicin, which are used to treat serious gram negative infections by injection, and inhibit protein synthesis. Serum levels need to be monitored as gentamicin is highly toxic.
Define the antimicrobial effect of macrolides and tetracyclines?
Macrolides (e.g. erythromycin, clarithromycin) and the tetracyclines both inhibit protein synthesis, and are useful alternatives to penicillin in those with penicillin allergies for the treatment of gram positive infections.
Define the antimicrobial effect of oxazolidinones
Linezolid is the only example of this new class of protein synthesis inhibitors. Has good activity against serious MRSA infections and given orally.
Define the antimicrobial effect of cyclic lipopeptides
Daptomycin is a novel agent used against serious gram positive and MRSA infections, and inhibits protein synthesis.
Which drugs inhibit purine synthesis?
Trimethoprim and sulphamethoxazole
What class of drugs includes trimethoprim and sulphamethoxazole, and what are they used for together?
Inhibit purine synthesis and commonly used in combined form co-trimoxazole to treat chest infections to reduce the risk of subsequent C.difficile infections
What is trimethoprim used for?
On its own for UTIs, and in conjunction with sulphamethoxazole for chest infections
Which bacteria are more susceptible to the action of penicillin and cephalosporins?
Gram positive organisms such as streptococci and staphylococci. Gram negative cell walls are relatively impermeable.
Give some examples of glycopeptides
Vancomycin and teicoplanin. These inhibit the assembly of a peptidoglycan precursors in gram positive organisms.
How are glycopeptides administered?
Parenterally (IV, not absorbed well orally)
What are aminoglycosides?
Inhibit protein synthesis e.g. gentamicin
What is gentamicin used for?
Inhibits protein synthesis, given IV to treat gram negative infections e.g. E.Coli and coliforms. Requires a careful dosing regime as it is highly toxic
Describe the macrolides and tetracyclines
Includes erythromycin and clarithromycin
Prevent protein synthesis
Used to treat gram positive infections in those allergic to penicillin
