Antibiotics Flashcards
What are antibiotics?
A drug used to treat or prevent infections caused by micro-organisms
Bacteriostatic
Inhibits the growth of bacteria
Bacteriocidal
Kills bacteria
Properties of an ideal antibiotic (x7)
- Selective toxicity, with minimal toxicity to host
- Bacteriocidal (kills bacteria)
- Long half-life (e.g. low binding to plasma proteins)
- DNA gyrases (DNA topoisomerase II) - helps in DNA unwinding
- Appropriate tissue distribution
- No adverse drug interactions (Reduces the risk of hypersensitivity)
- Oral and parenteral preparations (i.e. not intravenous)
Bacteria targets of inhibition (x5)
- Bacterial cell wall
- Inhibitors of RNA synthesis / translation
- Targeting DNA replication
- Targeting gyrases
- Targeting metabolic pathways
What is the process involved in cell wall synthesis?
Transpeptidation - formation of peptide bonds between the 3rd a.a. in one pentapeptide (usually mDAP) and the 4th a.a. in an adjacent pentapeptide, D-Ala, accompanied by the release of a 2nd D-Ala.
What possess transpeptidase activity?
Pencillin-binding proteins
What is the target of the Beta-lactams class of antibiotics?
Penicillin-binding proteins
Mode of action of B-lactam class of antibiotics
Bind to penicillin binding proteins, inhibiting their transpeptidase activity. This prevents the cross-linking of peptide side chains and cleavage of terminal D-Ala-D-Ala dipeptide, hence no energy is released and no peptide bridge (cross-links) can form.
What are autolysins?
Endogenous enzymes that degrade already mature peptidoglycan / the components of a biological cell or a tissue in which it is produced.
List the members of the beta-lactam class of antibiotics (x6)
- penicillin
- amoxicillin
- flucloxacillin
- co-amoxicillin
- cephalosporins
- carbapenems
Which antibiotic is used in the treatment of MRSA?
Vancomycin
Which component of the bacterial cell does vancomycin target?
Cell wall
How does vancomycin work?
Vancomycin binds to the terminal D-Ala-D-Ala end of peptide side chains, preventing their binding to PBPs, hence preventing its incorporation into the cell wall
Name the antibiotics that work by inhibiting RNA synthesis/translation (x6)
- Streptomycin (Aminoglycosides)
- Tetracycline
- Clindamycin (Lincosamides)
- Erythromycin (Macrolides)
- Fusidic acid
- Chloramphenicol
Name the antibiotics that work by targeting DNA Replication / DNA gyrase
- Ciprofloxacin
2. Metronidazole (Nitroimidazole)
What cells do streptomycin work on?
Gram-negative and some Gram-positive bacteria
Blocks the initiation complex on the 70S subunit
How do tetracyclines work?
Binds to the 30S ribosomal subunit and interferes with the binding of aminoacylated tRNA molecules to the ribosomal A site –> Preventing attachment and stops chain elongation
What treatment is clindamycin used in?
Osteomyelitis
bc of its tendency to concentrate in bone
What does erythromycin act on?
Gram-positive bacteria; Neisseria and Haemophilus
What does synergism mean in respect to antibiotic treatment?
Combined activity of antibiotics is greater than the activity expressed from the effect of each antibiotic
Mode of action of Metronidazole
The drug is activated under anaerobic conditions to form a toxic intermediate that induces DNA strand breakage
What are inhibitors of folic acid synthesis? (x2)
Sulphonamides
Trimethroprim
What do Quinolones target?
DNA replication, by preventing the supercoiling of DNA
Mode of action of Sulphonamides
Sulphonamides target metabolic pathways by inhibiting folic acid synthesis. They are analogues of para-aminobenzoic acid and inhibits pteridine synthetase
Mode of action of Trimethroprim
Sulphonamides target metabolic pathways by inhibiting folic acid synthesis. They are analogues of pyrimidine and inhibits dihydrofolate reductase.
What does metronidazole protect against?
Anaerobes and some parasites (protozoa)
