Antibacterials Flashcards
What are the main classes of antibacterials in clinical use?
- B-lactams
- Glycopeptides
- Tetracyclines
- Aminoglycosides
- Macrolides
- Quinolones
- Miscellaneous
What are the B-lactam antibiotics?
- Pencillins
- Penicillanase resistant pencillins
- Broad spectrum penicillins
- Cephalosporins
Give 2 examples of penicillins
- Phenoxymethylpenicillin
- Methylpenicillin
What organisms are susceptible to penicillins?
- Mainly gram +ve spp
- Some gram -ve spp
What is the main cellular target of penicillins?
Bacterial cell wall
What is the mechanism of action of penicillins?
Prevents peptidoglycan cell wall cross-linking
Give an example of a penicilliniase resistant penicillin
Flucoloxacillin
What is penicilliniase resistant penicillin used for?
Staphylococcal infections of soft tissues
Give two examples of broad spectrum penicillins
- Amoxicillin
- Ampicillin
What organisms are susceptible to broad spectrum penicillins?
Wide range of gram +ve and gram +ve spp
How many generations of cephalosporins are there?
3
Give an example of a first generation cephalosporin
Cefalexin
What organisms are susceptible to first generation cephalosporins?
Principally gram positive
Give an example of a second generation cephalosporin
Cefuroxime
How does the organism susceptibility differ between generation 1 and 2 cephalosporins?
Generation 2 has greater gram negative cover
Give an example of a third generation cephalosporin?
Cefotaxime
How does the organism susceptibility differ between generation 2 and 3 cephalosporins?
Generation 3 has even greater gram negative cover, but less gram positive (especially SA)
Give two examples of glycopeptides
- Vancomycin
- Teicoplanin
What organisms are susceptible to glycopeptide antibacterials?
Gram positive spp.
How common is resistance to glycopeptides?
Rare
Where is resistance to glycopeptides sometimes found?
- In enterococci
- (GRE)
- Some SA
Give 3 examples of tetracyclines
- Tetracycline
- Doxycycline
- Lymecycline
What organisms are susceptible to tetracyclines?
- Many gram +ve and gram -ve spp.
- Chlamydia,
- Mycoplasma,
- Rickettsia ab,
- Treponemesm,
- Plasmodium, and
- Entamoeba histolytica
What is the main cellular target of tetracyclines?
Bacterial protein synthesis
What is the mechanism of action of tetracyclines?
Locks tRNA to septal site of mRNA
Give two examples of aminoglycosidases
- Gentamicin
- Neomycin
What organisms are susceptible to aminoglycosidases?
- Many gram -ve spp
- Some gram +ve spp
What is needed when giving aminoglycosidases?
Careful monitoring
Why does administration of aminoglycosidases require careful monitoring?
Can lead to nephrotoxicity and toxicity to CNVIII
What is the cellular target of aminoglycosidases?
Bacterial protein synthesis
What is the mechanism of action of aminoglycosidases?
On 30S, prevents mRNA translation into proteins
Give 3 examples of macrolides
- Erythromycin,
- Clarithromycin,
- Azithromycin
What organisms are susceptible to macrolides?
- Gram +ve cocci
- Many anaerobes
- Mycoplasma
- Chlamydia
What anaerobes are not susceptible to macrolides?
Bacteroides
What are macrolides similar too in terms of organisms susceptible?
Pencillin
What is the result of penicillin and macrolides having similar organisms susceptible to them?
Macrolides can be useful in patients with a penicillin allergy
What is the clinical use of azithromycin?
Used to treat gonadal chlamydia trachomatis infection
What is a potential side effect of erythromycin?
Nausea
Why may erythromycin cause nausea?
Due to its action on the gut
What is the site of action of macrolides?
Bacterial protein synthesis
What is the mechanism of action of macrolides?
Binds to 50s
Give 3 examples of quinolones
- Ciprofloxacin
- Levofloxacin
- Norfloxacin
What organisms are susceptible to quinolones?
Gram -ve and gram +ve spp
What is the clinical use to ciprofloxacin?
Used to treat urinary tract sepsis, biliary tree sepsis, food poisioning due to Campylobacter
What does ciprofloxacin have a good action against?
Pseudomonas spp (especially P. areuginosa)
What is the cellular target of quinolones?
Bacterial DNA
What is the mechanism of action of quinolones?
Inhibiting bacterial DNA gyrase which inhibits coiling, leading to DNA damage
What the the miscellaneous antibacterials?
- Metronidazole
- Suphonamides and trimethoprim
- Antimycobacterials
What organisms are susceptible to metronidazole?
Covers all anaerobes and some protozoa;
- Giardia,
- Entamoeba histiolytica
- Trichomonas vaginalis
What is the clinical use of metronidazole?
Treatment of pseudomembranous colitis
When is metronidazole well tolerated?
If taken without alcohol
What is the cellular target of metronidazole?
Bacterial DNA
What is the mechanism of action of metronidazole?
Forms toxic metabolites which inhibit nucleic acid synthesis
What is the clinical use of sulphanoamides and trimethoprim?
- Now less commonly used in bacterial infections, except trimethoprim is first line treatment for uncomplicated UTI.
- Important use in prophylaxis and treatment of PCP.
- Used for some protozoan infections.
What is used to treat PCP?
Co-trimoxazole (septrin)
What is the cellular target for sulphanoamides and trimethoprim?
Bacterial folate metabolism
What is the mechanism of action of suphonamides and trimethoprim?
Inhibits DHFR
What are the antimycobacterials?
- Rifampicin
- Isoniazid
- Pyrazinamide
- Ethambutol
What are antimycobacterials used for?
Treat mycobacterial infections- TB
