Antibacterials Flashcards
What are the different sites where antibiotics can act?
Cell wall synthesis
DNA synthesis
Protein synthesis
Which types of antibiotics inhibits cell wall synthesis?
Beta lactams
Glycopeptides
Which antibiotics inhibit DNA synthesis?
Quinolones
Folic acid antagonists
Which antibiotics inhibitprotein synthesis?
Tetracyclines
Aminoglycosides
Macrolides
What is an example of a beta lactam?
Penicillin
Cephalosporins
Carbapenems- eg meropenem
What is an example of a glycopeptide?
Vancomycin
What is an example of a quinolone?
Ciprofloxacin
What are some examples of folic acid antagonists?
Trimethoprim
Sulphonamides
What are the major indications for use of antibiotics?
Therapy of clinically significant bacterial infections- either empirical treatment of suspected infection or treatment of culture proven infection
Prophylaxis- eg peri op, short term meningitis contacts
Long term- asplenia, immunodeficiency
What are the factors governing antibiotic choice accounting for likely infectious agent and patients to be used in?
Time of year Anatomical site Travel history Duration of illness PMH Occupational history
What are the common side effects of antibiotics?
Toxicities
Allergic reactions
Ecological effects- eg C.dificile infection
Drug reactions
How does antibiotic resistance arise?
Chromosomal mutation
Horizontal gene transfer
Why do some bacteria have resistance to beta lactams such as penicillins, cephalosporins and carbapenems?
All drugs in this class must have a B lactam ring which must be intact for them to be active. This is vulnerable to attack by beta lactamase attack.
What is the mechanism of action of beta lactam antibiotics?
These bind to several penicillin binding proteins in bacteria. Some of these are transpeptidases that are required for cross linking of the peptidoglycan layer of the cell wall. This prevents it making an intact cell wall when it divides.
What are the pharmacokinetics of penicillins?
Widely distributed across body. Short half lives due to rapid elimination by kidney.
What are the clinical indications of penicillin G?
Active against many aerobic gram positive bacteria, a more limited range of gram negative bacteria such as gonococci and meningococci.
Are gram negative bacilli sensitive to penicillin G?
No
What is the clinical indication for flucloxacillin?
Beta lactamase resistant. Therefore reserved for beta lactamase producing staphylococci.
What is the clinical indication for ampicillin and amoxicillin?
Gram negative bacilli. Less effective against gram positive cocci. Inactivated by B lactamase.
What are the side effects of penicillins?
Nausea Allergic reactions-fever, vasculitis, steven johnson syndrome, anaphylactic shock. Aminopenicillins commonly produce a non allergic maculopapular rash in people with glandular fever. Does not recur if another type of penicillin is given. Reversible neutropenia and eosinophilia Encephalopathy Diarrhoea C. Dif related colitis Cholestatic jaundice.
What is the clinical indication of 3rd generation cephalosporins such as cefotaxime, ceftriaxone and cefixime?
Gram negative bacilli. Can cross blood brain barrier.
What are the pharmacokinetics of cephalosporins?
2nd and 3rd generation must be given parenterally. Most are excreted by kidney and have short half lives.
What are the side effects of cephalosporins?
Nausea, vomiting, abdo discomfort Headache Rashes Similar allergic reactions to penicillins C.dif related colitis
Which antibiotic is commonly now being used more and more in place of trimethoprim for lower urinary tract infections?
Nitrofurantoin
What is the mechanism of action of nitrofurantoin?
inhibits DNA synthesis.
Which bacteria is nitrofurantoin active against?
Many gram positive cocci and E coli.
What are some examples of macrolides?
Azithromycin, clarithromycin, erythromycin
What are some examples of aminoglycosides?
Gentamicin, streptomycin
What is the mechanism of action of aminoglycosides?
They bind to 30s ribosome subunit and prevent protein synthesis.
What is the spectrum of activity of aminoglycosides?
Active against many gram negative bacteria and some gram positive bacteria. Inactive against anaerobes.
What are the major side effects of aminoglycosides?
Ototoxicity
Nephrotoxicity
What are some examples of tetracyclines?
Doxycycline, minocycline
What is the mechanism of action of tetracyclines?
Inhibition of 30 s subunit of ribosomes.
What is the spectrum of activity of tetracyclines?
Many G+ and G- bacteria. Also effective in chalmydia infections.
What are the most common infecting organisms in sinusitis/ otitis media which has failed to resolve after 7 days?
Which antibiotics can be used to treat them?
H. Influenzae, S. Pnuemoniae, Moraxella catarrhalis.
Suitable drugs would include amoxicillin, doxycycline and clarithromycin.
Which organisms commonly cause community acquired pneumonia?
S. Pneumoniae, H. Influenzae, staphylococci. Atypical micro organisms include legionella, mycoplasma pneumoniae or chlamydia pneumoniae.
Which antibiotics would be a good choice for CAP?
Amoxicillin if pneumococcus is suspected
Clarithromycin will cover most organisms.
Severe CAP (high CURB 65 score) is treated with IV therapy including penicillin G with clarithromycin or doxycyclin.
Which antibiotics are often used for hospital acquired pneumonia?
Cefuroxime, co amoxiclav used for early onset infections.
Ciprofloxacin for late onset infections. Aminoglycoside such as gentamicin can be added for severe infection if P. Aeruginosa is suspected.
What are the bacterial causes of gastroenteritis?
E.coli, salmonella, campylobacter, V.cholerae, shigella.
What treatment is commonly prescribed for bacterial gastroenteritis?
Fluid replacement.
If there are severe symptoms then- ciprofloxacin and clarithromycin are effective for campylobacter and shigella. Salmonella can be treated with ciprofloxacin.
