Antibiotics Flashcards
What is an antibiotic?
A drug used to treat an infection caused by bacteria
What are the four general mechanisms of antibiotic action?
Disruption of bacterial cell wall
Inhibit nucleic acid synthesis
Inhibit protein synthesis
Antimetabolite activity
Which groups of antibiotics mechanism of action is to disrupt the bacterial cell wall?
Beta-lactams
- penicillins
- cephalosporins
- carbapenems
- monobactems
Glycopeptides
How do beta-lactams disrupt the bacterial cell wall?
Form covalent bonds with penicillin-binding protein to inhibit final formation of cross links
How do glycopeptides disrupt the bacterial cell wall?
Inhibit the release of the building block unit from the cell membrane.
Prevent addition to growing end of the peptidoglycan
Damages cytoplasm
Give examples of penicillins
Simple (susceptible to Beta-lactamases):
- Penicillin V
- Benzylpenicillin
- Amoxicillin
Resistant (prevent ring breakdown):
- Flucloxacillin
- Co-amoxiclav
What are the uses of simple penicillins?
Gram +ve cocci - e.g. streptococcus
Gram -ve cocci/bacilli - e.g. listeria
Spirochetes - e.g. Syphilis
What are the uses of resistant penicillins?
Same as simple penicillins, but also for Staphylococcus
What infections can penicillin be used against?
RTIs
UTIs
Skin infections
Ear infections
What are the side effects of penicillins?
Hypersensitivity ~10% (~0.2% anaphylaxis)
Diarrhoea
Give examples of cephalosporins
1st generation
- Cephradine
- Cephalexin
2nd generation
- Cefuroxime
3rd generation
- Cefotaxime
- Ceftriaxone
What are the side effects of cephalosporins?
Similar to penicillin
i.e. hypersensitivity, diarrhoea
Which cephalosporin would be used to treat meningitis?
Cefotaxime (3rd)
Ceftriaxone (3rd)
Which cephalosporin would be used to treat pseudomonas?
Ceftriaxone (3rd)
Which cephalosporin would be used to treat community acquired meningitis?
Cefuroxime (2nd)
Which cephalosporin would be used to treat skin/soft tissue infection?
Cephradine (1st)
Cephalexin (1st)
Give an example of a glycopeptide?
Vancomycin
not absorbed orally, althought can treat GIT infection
Which conditions might you use glycopeptides for?
MRSA
Resistant C. Difficile
(Usually administered I.V. - not absorbed otherwise)
What are the side effects of Glycopeptides?
Ototoxic - ear and its nerve supply
Nephrotoxic - kidneys
“Red Man Syndrome” - Hypersensitivity reaction
Which groups of antibiotics mechanism of action is to inhibit nucleic acid synthesis?
Quinolones
Metranidazole
Rifampicin
Which groups of antibiotics mechanism of action is to inhibit protein synthesis?
Macrolides
tetracyclines
Aminoglycosides
Chloramphenicol
Which groups of antibiotics mechanism of action is antimetabolite activity?
Trimethoprim
Sulphonamides
How do quinolones inhibit nucleic acid synthesis?
Inhibit DNA gyrase enzyme to prevent supercoiling of bacterial DNA
Give examples of quinolones
Ciprofloxacin
Levofloxacin
i.e. -oxacin
How does metranidazole inhibit nucleic acid synthesis?
Damage DNA by forming reactive intermediates that inhibit DNA synthesis
How does rifampicin inhibit nucleic acid synthesis?
Inhibit RNA polymerase to prevent transcription of mRNA
What are Quinolones used for?
Broad spectrum antibiotic, although usually 2nd line
Especially used against pseudomonas
- only oral Abx that works
What can inhibit the absorption of quinolones?
Metals
What are the contraindications and interactions of quinolones?
CI:
- Epilepsy - reduces seizure threshold
- Children
Interactions:
- Warfarin
What is metranidazole used for?
Effective against anaerobes
Abdo, GI and Perineal infections
What are the side effects / interactions of Metranidazole?
Alcohol interaction
- Vomiting
- tachycardia
- dyspnoea
What is Rifampicin used for?
Used in Mycobacteria, especially Tuberculosis (RIPE - used in combo)
What are the side effects / interactions of Rifampicin?
Induces P450s
- Th. any drugs that are metabolised by P450s have increased efficacy
Stains contact lenses orange
How do macrolides inhibit protein synthesis?
Binds to 50S subunit and inhibits translocation (where tRNA in A site is moved along to the P site)
How do tetracyclines inhibit protein synthesis?
Binds to the 30S subunit of the ribosome.
Actively competes with the tRNA for the A site to inhibit its binding.
How do aminoglycosides inhibit protein synthesis?
Binds to 30S subunit of the ribosome.
Causes misreading of codon on the mRNA, resulting in non-functional proteins produced
How does chloramphenicol inhibit protein synthesis?
Inhibits transpeptidation (where the growing peptide chain attached to the P site is transferred to the amino-acid attached to tRNA in A site)
Give examples of macrolides
Erythromycin
Clarithromycin
Give examples of tetracyclines
Doxycycline
Oxytetracycline
Tetracycline
Give examples of aminoglycosides
Gentamicin
Tobramycin
Amikacin
Which antibiotics are used as a penicillin replacement?
Macrolides
What are the indications of macrolides?
Substitute for penicillin = similar effects
More SE though
What are the side effects/interactions of macrolides?
Inhibit liver metabolism of warfarin and statins
=> may induce OD on these drugs - withhold statins
Diarrhoea and Vomiting
What are the indications of tetracyclines?
Skin/soft tissue infection (mostly)
Acne
What are the side effects of tetracyclines?
Photosensitivity
What are the interactions of tetracyclines?
Children, Pregnancy, Breastfeeding
- Incorporated into bone/teeth = causes discolouration and growth stunting
What are the indications of aminoglycosides?
RTIs and tuberculosis
administered IV only
Waht are the side effects of aminoglycosides?
Oxotoxicity (Ear) - especially in elderly
Nephrotoxicity (Kidney)
What is the action of trrimethoprim?
Inhibits the usage of folate
What is the action of sulphonamides?
Inhibit mechanism of folate synthesis
What are the indications for trimethoprim?
Used mostly in UTIs
- Excreted unchanged in high quantities in urine
What are the side effects of trimethoprim?
Rare but serious side effects therefore only if risk-benefit balance is good
Which antibiotics should be used for infection as a result of stones?
IV Ampicillin
IV Gentamicin
