Antibiotics Flashcards
How do penicillins and cephalosporins work?
Inhibits bacterial cell wall synthesis by preventing cross linking between peptidoglycan chains
What is amoxicillin used for?
Has activity against gram +ve (strep, staph) and gram -ve (H.influenzae, E.coli) bacteria. Commonly susceptible infections include UTIs, otitis media, sinusitis, uncomplicated CAP, salmonellosis, oral infections. Also used in combination in H.pylori eradication
Which strains of bacteria would rule out amoxicillin (and other Beta lactam) use?
Bacteria that produce beta lactamase enzymes.
What are the cephalosporin generation drugs?
1st gen - cefradine
2nd gen - cefuroxime
3rd gen - cefotaxime
Less activity against gram +ve bacteria the higher the generation. 2nd gen less susceptible to beta lactamase inactivation. 3rd gen greater activity against certain gram -ve bacteria
What is a common side effect to be wary of when using the cephalosporins?
Antibiotic-associated colitis
Interaction of cephalosporins with aminoglycosides?
Increased risk of nephrotoxicity
How do antifolate antibiotics Trimethoprim and Sulfonamides work?
Inhibit folate synthesis. Trimethoprim inhibits dihydrofolate reductase, sulfonamides inhibit diaminopteroate synthetase. Combined as co-trimoxazole
What is trimethoprim commonly used to treat?
UTIs. Can also be used in resp-tract infections, acne resistant to other Abx, prostatits, shigellosis, invasive salmonella
What is the interaction of trimethoprim and sulfonamide use with methotrexate?
Increased risk of severe bone marrow depression
Why is trimethoprim and sulfonamides use becoming a problem?
Resistance is common
How does nitrofurantoin work?
Broad spec ABx that inhibits DNA, RNA, protein and cell wall synthesis
What is nitrofurantoin used for?
UTIs. Effective against E. Coli, Enterobacter cystitis, Enterococcus, Klebsiella, and Staphylococcus aureus
Contraindications to nitrofurantoin use?
Acute porphyrias, G6PD deficiency, infants < 3 months old
Which strain of bacteria is completely resistant to nitrofurantoin?
All pseudomonas strains
What type of antibiotic is doxyxycline?
Tetracyclines
How does doxycycline work?
Protein synthesis inhibitor, inhibits RNA translation
What is doxycycline used for?
Susceptible infections caused by chlamydia, rickettsia, mycoplasma
Why should doxycycline use be cautioned with myasthenia gravis and SLE?
Can increase muscle weakness in myasthenia gravis and exacerbate SLE
Why should doxycycline and other tetracyclines not be given to children under 12 or pregnant women?
Doxycycline deposits on teeth and bone, causing staining and dental hypoplasia
Examples of aminoglycosides?
Gentamicin, streptomycin
How does gentamycin work?
Protein synthesis inhibitor, binds to 30S subunit
Indications for aminoglycoside use?
Serious aerobic gram -ve infections and staph. Gentamycin against P. aeroginosa, streptomycin against M. tuberculosis
Why is aminoglycoside use contraindicated in those with myasthenia gravis?
NMJ transmission can be impaired
Side effects to be wary of with aminoglycosides?
Ototoxicity and nephrotoxicity
Why is drug monitoring essential when on aminoglycosides?
Narrow therapeutic index, also not normally used for more than 10 days due to toxicity risk
What is often used in combination with aminoglycosides in streptococcal endocarditis/other serious infections in blind therapy?
Beta lactams such as penicillin
What syndrome can be caused in neonates if aminoglycosides have been used?
Grey baby syndrome
What type of antibiotic is erythromycin?
Macrolide
How does erythromycin work?
Protein synthesis inhibitor, inhibits protein elongation
Why is clarithromycin given BD whilst erythromycin is given QDS?
Clarithromycin has greater activity and better tissue availability
What is erythromycin used for?
Similar spectrum to penicillins so used as alternative in pen allergic patients. Gram +ve (and some gram -ve) infections
Why is erythromycin enteric coated?
It is adversely affected by gastric acid
Why are only short courses of macrolides given?
Resistance is quite rapid, >14 days use increases risk of hepatic damage
Example of quinolone?
Ciprofloxacin
How does ciprofloxacin work?
Inhibits DNA gyrase and topoisomerase IV which are involved in DNA remodelling. (Humans don’t have DNA gyrase)
What is ciprofloxacin used for?
Broad spec. Particularly active against gram -ve bacteria (campylobacter, neisseria, pseudomonas)
What type of weather should be avoided when on quinolones?
Excessive sunlight
How does metranidazole work?
Broken down to toxic compounds within anaerobic microbes.
What is metranidazole used for?
Anaerobic protozoal infections, H.pylori infection, rosacea, pseudomembranous colitis
Why can’t alcohol be consumed when using metranidazole?
Disulfiram-like reaction can occur (flushing/abdo pain/hypotension)
What type of antibiotic is vancomycin?
Glycopeptides
How does vancomycin work?
Inhibits cell wall synthesis
What is vancomycin used for?
Gram +ve infections both aerobic and anaerobic including MRSA. Treatment of endocarditis and C.diff
Why should vancomycin not be given PO for systemic infections?
Poorly absorbed
Side effects of vancomycin?
Ototoxic and nephrotoxic, blood disorders, N, chills, fever, flushing of upper body ‘red man’ syndrome
Which antibiotics are safe to use in pregnancy?
Penicillins and cephalosporins
Which antibiotics are NOT safe to use in pregnancy?
Chloramphenicol, tetracyclines, fluouroquinolones, co-trimoxazole
Tazocin is a combination of which drugs?
Piperacillin and tazobactam
Vancomycin only has activity against which type of organism?
Gram +ve bacteria
Aztreonam only has activity against which type of organism?
Gram -ve bacteria
