Antibiotics 1 Flashcards
what is an antibacterial?
substances used to disinfect non-living surfaces
what are the gram positive rods that produce antibiotics?
bacillus subtilis and paenibacilus polymyxa
what other drugs produce antibiotics?
streptomyces, cephalosporin and penicillium
what are antibiotics classified by?
their mechanism, chemical structure, spectrum of activity
what are some of the target sites of antibiotics?
cell wall synthesis, protein synthesis, nucleic acid action and injury to a plasma membrane
what drugs inhibit cell wall synthesis?
pencillins, cephalosporins, bacitracin and vancomycin
what does erythromycin, tetracyclines and streptomycin do?
cause inhibitor of protein synthesis
what do quinolone do?
cause inhibition of nucleic acid replication and transcription
what does rifampin do?
cause inhibition of protein synthesis
what drugs cause injury to the plasma membrane?
polymyxin B
what do beta lactams do?
effect cell wall construction
what drugs inhibit protein synthesis?
ahminoglycosides, tetracyclines, lincosamine and macrocodes
what are the desired properties of antimicrobials?
selectivity, broad spectrum
what are the desired pharmacological properties?
non-toxic to host, good tissue distribution, low plasma-protein binding, no interference with other drugs
what is selectivity toxicity?
kills harmful microorganisms without damaging the host
how is selective toxicity achieved?
the target sites of the drugs are specific to the microorganism
what is the therapeutic index?
ratio of toxic dose to therapeutic dose
what is bactericidal activity?
antibiotics that target bacterial cell wall or interfere with essential enzymes
what is bacteriostatic activity?
slows the growth of bacteria
what factors effect concentration?
dose, route of administration, absorption, extent of protein binding, rate of metabolism, rate of excretion
what must the concentration of the antibiotic be in order to be effective?
must reach a concentration that is above the bacteriums MIC to be effective
what is the mechanism of action of polymyxins?
to selectively act on membranes rich in phosphatidylethanolamine
what bacteria is polymyxins effective on?
gram negative rods including pseudomonas
what kind of bacteria is polymyxins not effective to?
gram positive bacteria
what are the pharmacodynamic features of polymyxin?
not absorbed after oral administration because of multiple positive charges, cross membranes poorly, not well distributed and eliminated via kidneys
what is a common clinical use of polymyxin?
used in topical triple antibiotic locations with neomycin and bacitracin
why is polymyxin rarely used systemically?
highly toxic
what are the adverse reactions of polymyxin?
nephrotoxicity and neurotoxicity
what are the chemical structural features of polymyxin?
has hydrophobic tail ands a cyclic peptide
how can targeting of cell walls help provide a more specific target?
mammalian cells do not have a cell wall so it provides a target for chemotherapy
what antibiotics target the cell wall?
beta lactams, cephalosporins, vancomycin and bacitracin
what antifungals target the cell wall?
cilofungin interferes with biosynthesis of beta gluten in fungal cell wall
what does cycloserine do?
inhibits peptidoglycan precursor formation inside the cell
what does bacitracin and vancomycin do?
inhibits transport and peptidoglycan formation in the cell membrane
what do penicillin and cephalosporins inhibit?
cross linking of peptodoglycans that occurs outside the cell
what steps of cell wall synthesis does cycloserine inhibit?
d-alanyl-d-alanyl synthesis and d-alanine-d-alanine ligase
what is cycloserine used to treat?
tuberculosis
what is undecaprenyl phosphate?
a carrier required during peptidoglycan synthesis
what does bacitracin do to prevent peptidoglycan synthesis?
inhibits the dephospho rylation of undecaprenyl phosphate to produce the carrier needed for synthesis
what does vancomycin bind to?
the d-ala-d-ala terminus of the cell wall precursor units
how does vancomycin prevent cell wall synthesis?
binds to the terminus and prevents cross-linking and polymerisation of peptidoglycan
what kind of spectrum does vancomycin have?
narrow
what are the clinical uses of vancomycin?
MRSA
how is some bacteria able to be resistant to vancomycin?
vancomycin cannot bind to the D-lactate residues and so peptide chains form stable cross-links
what is the chemical structure of cephalosporins?
a beta lactam cyclic amide ring attached to a 6 membered ring
what is the chemical structure of penicillin and panems?
4 membered cyclic amide ring attached to a 5 membered ring
what is the structure of a monobactam?
a 4 membered cyclic amide ring attached to no other rings
what do betalactams inhibit?
transpeptidase reaction
what is the substrate forget lactamases?
penicillin binding protein
what is the transpeptidase reaction?
catalysing of the cross linking of the bacterial peptidoglycan during cell wall synthesis
what is a PBP?
they create the cross links in the cell wall
how might PBP’s lead to antibiotic resistance?
altered PBP’s may confer resistance to antibiotics
what is penicillinase also known as?
beta lactamase
what effect does penicillinase have on penicillin?
the beta lactam ring in active penicillin is broken open so that it becomes inactive
