Antibiotics (2/2) Flashcards
beta lactam antibiotics
This is an umbrella group that encompasses four families of antibiotics: penicillins, cephalosporins, carbapenems and monobactams.
most penicillins have the suffix
‘-cillin’
penicillins all interfere with the
third and final stage of bacterial cell wall synthesis
important penicillins to remember
- benzylpenicillin (usually just referred to as penicillin)
- amxoicillin
- flucloxacillin
- co-amoxiclav
which bacteria are penicillins affective against and why
gram positive (streptococci mainly)- have thicker and exposed cell wall
which penicillin has some activity against gram-negative bacteria?
amoxicillin
flucloxacillin is effective against
straphlococci and streptococci
co-amoxiclav is a
combination of amoxicillin and clavulanic acid ( a beta lactase inhibiter)
what can make amoxicillin less effective
bacteria such as staphylococcus aureus can excrete beta-lactamase reducing antibacterial efficacy as it breaks down the antibiotic. The clavulanic acid inhibits the beta-lactamase allowing amoxicillin to function for longer without being broken down
co-amoxiclav is effective against
Staphylococci, Streptococci, Gram-negative bacteria and gives it an effect on anaerobic bacteria as well.
cephalosporins
There are considered to be five generations of cephalosporins but each of them works by inhibiting cell wall synthesis. q
how are cephalosporins (a beta lactam) different to penicillins
cephalosporins have no activity against anaerobic bacteria but are otherwise quite broad spectrum.
name a cephalosporin
ceftriaxone
ceftriaxone is used to treat
meningitis - good level of activity in the cerebrospinal fluid (can cross BBB)
cephalosporins and clostridium difficile infection
C. diff is a commensal bacterium found in your normal gut microbiome that competes for nutrients with other flora. This constant competition prevents C. diff overgrowth. Cephalosporins can also eliminate some of the natural gut flora as well as the pathogenic organism in an infection. This reduces competition allowing for C.diff to proliferate and over grow causing disease.
carbapenems example
meropenem
what is meropenem active against
Alongside Gram-positive and Gram-negative bacteria, it is active against anaerobic bacteria
what is meropenem strongest against
strongest against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, though it is not effective against MRSA.
why would you not prescribe meropenem to someone with a penicillin allergy
similar structure to penicillin
what the main glycopeptide (another class of antibiotic)
vancomycin
glycopeptides inhibit what
cell wall synthesis by preventing two subunits from being incorporated into the peptidoglycan matrix that is the core structural component of the cell walls of Gram-positive bacteria
vancomycin is active again
both aerobic and anaerobic bacteria
important to remember about vancomycin
does have a narrow therapeutic window, so the patient needs to have therapeutic drug monitoring to ensure that the dose does not become toxic.
why is vancomycin a last resort drug
still many bacteria that are not resistant to it, including multiresistant staphylococci and Clostridium difficile, so it is only given when absolutely necessary to prevent sudden overuse and resistance among bacteria
how is vancomycin delivered
given IV (esp for systemic infection) because it isn’t absorbed via the gut (except int he case of C .diff infection whereby it is given orally to target GI)
other glycopeptide of note other than vancomycin
teicoplanin
teicoplanin more poplar than vancomycin because
his has a larger therapeutic index and is therefore much easier to monitor with the risk of a toxic dose less likely.
what are the two main tetracyclines
tetracycline and doxycycline
mode of action of doxycycline and tetracycline
Both are bacteriostatic antibiotics through their action of inhibiting protein synthesis of the bacteria (this holds them in the stationary phase of their growth cycle instead of killing them outright (bactericidal)).
both doxycycline and tetracycline are
broad spectrum antibiotics
what sort of infections are doxycycline and tetracycline useful in treating
a good choice for patients with a penicillin allergy that you are treating for a Gram-positive bacterium.
what sort of illnesses are doxycycline and tetracycline affective against
Chlamydia, rocky mountain spotted fever and typhoid fever
what should doxycycline and tetracycline not be used to treat
Streptococcal infections as up to 44% of S. pyogenes and 74% of S. faecalis have been found to be resistant to tetracyclines. This is why they are decreasing in value except in a number of different illnesses or patients with penicillin allergies (e.g. in leptospirosis as an alternative to erythromycin).
why can tetracycline not be given to children younger than 12 years old or pregnant women
as it causes yellowing of the teeth among other adverse effects.
Bioavailability of tetracycline is
100% via IV, but only 40% via intramuscular (IM).
macrolides work by
inhibiting protein synthesis
name three macrocodes
erythromycin, clarithromycin and azithromycin
macrolides have a similar spectrum of action as penicillins
which make them a good alternative in patients with a penicillin allergy (mild gram-positive)
what is erythromycin used to treat
atypical pathogens in pneumonia, Legionnaires’ disease, early syphilis and Chlamydia.
erythromycin does not have great activity against
Haemophilus influenza
A way to work around this is the combination of erythromycin with a sulphonamide which will result in activity against a number of strains of H. influenzae.
side effects of erythromycin
tends to make patients nauseous, vomit or give them diarrhoea. If a patient has a mild infection then a lower dose can be prescribed, but when the infection is more serious (such as with a Legionella infection/pneumonia) then a higher dose needs to be prescribed.
azithromycin can attack
H influenza and other gram-negative bacteria
Clarithromycin dervived from erythromycin) treats
Helicobacter pylori infections (along with metronidazole and proton pump inhibitors)
quinolones work by inhibiting
bacterial replication through inhibiting DNA gyrase.
in the UK the only quinolones available to prescribe are
fluoroquinolones
name a fluoroquinolone
ciprofloaxin
ciprofloxacin is best against
Gram negative bacteria such as Escherichia coli, Salmonella and Shigella. It is only moderately active against Gram-positive bacteria such as Streptococcus, and a lot of Staphylococci are resistant to quinolones so make sure not to use them in MRSA infections.
risk when taking quinolones
C.diff infection
how can ciprofloxacin be used
an eye drop, ointment, orally and IV
ciprofloxacin used to treat
UTIs, GI infections, Gonorrhoea and septicaemia due the bacteria that it affects.
which other antibiotics not within the classes mentioned inhibit bacterial replication
trimethoprim and sulphonamides
trimethoprim works by
works to inhibit dihydrofolate reductase, an enzyme that is important in the folic acid cycle. Dihydrofolate reductase’s normal role is the conversion of dihydrofolic acid to tetrahydrofolic acid in the thymidine synthesis pathway
trimethoprim is often combined with
a sulphonamide, sulfamethoxazole, which are bacteriostatic antibiotics. As a side note, sulfamethoxazole acts on dihydrofolate synthetase, which is involved further upstream in the folic acid pathway
what is trimethoprim and sulphonamide together called
co-trimoxazole- more effective than either of its standalone components.
co-trimoxazol used to treat
uncomplicated pyelonephritis
COPD exacerbation
pneumocystis penumonia
trimethoprim alone is commonly used to treat
UTIs, acne, prostatitis and shigellosis.
trimethoprim should not be prescribed to
to a pregnant patient, particularly during the first trimester when folic acid supplements are often given to help with foetal development
metronidazole main target
anaerobic bacteria and protozoa
what sort of infections is metronidazole used to reeat
H. pylori
Fistulae in Crohn’s disease
Bacterial vaginosis
Pelvic inflammatory disease
Ulcerative gingivitis
Amoebiasis
Trichomoniasis
Giardiasis
Clostridium difficile.
Normally for anaerobic infections metronidazole is prescribed for
7 days
when a patient has C diff how long is metronidazole prescribed
10 to 14 days
with C diff infection what is emtronidazole co-prescribed with
omeprazole/lansoprazole and clarithromycin/amoxicillin
