M15- Antibiotics Flashcards
what is an antibiotic?
a drug used to treat or prevent infection caused by micro-organisms
what is bacteriostatic?
inhibit growth of bacteria
what is bactericidal?
kill bacteria
How can antibiotics be narrow spectrum or broad spectrum?
-e.g. Penicillin narrow spectrum active against Gram-positive bacteria
• Tetracycline active against many Gram-positive & Gram-negatives
what are antibiotics not a substitute for?
functional immune system
what are features of an ideal antibiotic?
• Selective toxicity/minimal toxicity to host • Cidal – (i.e. kills bacteria) • Long half life – (e.g. low binding to plasma proteins) • Appropriate tissue distribution • No adverse drug interactions/side effects • Oral & parenteral preparations
Name 3 antibiotic targets.
- cell wall (peptidoglycan synthesis)
- ribosomes (protein synthesis)
- DNA replication (nucleic acid synthesis)
what is cell wall synthesis targeted by?
ß-lactam (penicillins) & Glycopeptide antibiotics
How does penicillin work?
prevents cross linking of bacterial cell wall
Name 3 beta-lactams.
- Penicillin V (narrow spectrum)
- Amoxicillin (entended spectrum)
- Co-amoxiclav (inhibits b-lactamase)
What is the main B-lactams prescribed by dentists?
amoxycillin
what are features of amoxycillin?
- spectrum extended
- absorbed through intestine
- stable in presence of stomach acid
- peak plasma concentration 60-120 minutes after taking
- wide tissue distribution
- 20% binds to plasma proteins
- plasma half life is 60 minutes
what is not suitable for empiric prescribing?
co-amoxiclav
what are the features of penicillin V?
- narrower spectrum
- absorbed through intestine
- sensitive to stomach acid
- peak plasma concentration 30-60 minutes aft6er taking
- 75%-90% binds to plasma proteins
- serum levels maintained for 30-60mins
what are the advantages of B-lactam antibiotics?
– Well characterised
– Safe
– Spectrum (narrow to wide)
– Variety/choice
what are the disadvantages of B-lactam antibiotics?
– Resistance
– Rapidly excreted
– Hypersensitivity (1-10%) – CDI (C. diff infections)
what is the caution when using B-lactam antibiotics?
- Antibiotic antagonism
- Penicillin & bacteriostatic antibiotics
what are not B-lactam antibiotics but similar mode of action ?
Glycopeptides
How does glycopeptides work?
• Cell-wall active antibiotics,
– Binds to end of peptide side chains (D-alanine D-
alanine) & prevent its incorporation into the cell wall.
– Blocks access to substrate by PBP (transpeptidase)
– Inhibits peptidoglycan synthesis,
– Reduced cross-linking & activity of lytic enzymes
weaken the bacterial cell wall
• Bactericidal
Name some antibiotics that target protein synthesis?
- tetracyclines - deoxycycline
- macrolides - erythromycin
Name the features of gentamicin (aminoglycosides).
- not absorbed from gut -intravenously
- binds to ribosomes inhibiting protein synthesis: bactericidial
- active against gram negative
- excreted in urine
- toxicity -so monitored blood levels
what is the mode of action of tetracyclines (bacteriostatic ) ?
Actively transported into cell. Binds to 30S subunit. Prevents attachment of tRNA to acceptor sites. Stops chain elongation
what are the adverse effects of tetracyclines?
Destruction of normal intestinal flora resulting in increased secondary infections
what is the mode of action of lincosamides (bacteriostatic)?
– Bind to the 50S ribosome. Blocks Peptidyl-transferase.
– Prevents peptide Bond Synthesis.
what does the macrolides (erythromycin ) group do/
- excreted via the liver,
biliary tract and into the gut. – not excreted in urine - Lipophilic antibiotics pass through cell membranes easily.
– They are useful for treating certain infections where intracellular bacteria “hide” from the host’s immune system
– Erythromycin is safe in pregnancy
Name an antibiotic that inhibits nucleic acid synthesis?
metronidazole
-anaerobes and protozoa
How does metronidazole work ?
anaerobic conditions important beacuse its taken up into cell into inactive form - in reducing conditions becomes activated (charged molecule) -interfere and causes damage to DNA and leads to death
what is the mode of action of Quinolones (bactericidal)?
Bind to the A subunit of DNA gyrase (topoisomerase) and prevent supercoiling of DNA. Indirectly inhibit DNA synthesis
Name some side effects of antibiotics.
• Nausea, vomiting, diarrhoea – common – all antibiotics disrupt the gut bacterial flora
– may affect absorption of oral contraceptives
• Gentamicin
– renal & VIII nerve damage
• Metronidazole
– interacts with alcohol
• Broad spectrum antibiotics increase the risk of C. difficile infection in the elderly
what are the 4 “C” antibiotics that we try avoid using and why?
These broad-spectrum antibiotics are particularly associated with an increased risk of Clostridium difficile (“C diff”) infection: – Cephalosporins – Co-amoxiclav (MAIN) – Ciprofloxacin – Clindamycin
