Antibiotics

Question 1

AMOXICILLIN

i) what time of penicillin is it? give three reasons why this is good?
ii) which bacteria is it used to treat against (3)
iii) what is its mechanism of action?
iv) is oral bioavil good? what is 1/2 life? how is it excreted?
v) name two adverse effects? name an interaction
vi) mech of resistance?

Answer 1

i) aminopenicillin - good oral bioavail, longer half life than penicillin V and better activity against some gram negative bacteria

ii) good against s.pyogenes (sore throat and skin infec)
pneumococcal infection (resp tract)
coliform infection (UTI)

iii) inhibits bacterial cell wall synthesis
iv) good bio avail, 1 hour half life, excreted in urine

v) adverse = allergy and damage to commensals
interaction = can increase levels of other protein bound drugs

vi) Inactivation by bacterial beta-lactamases and alteration of PBPs, which reduce the affinity of the antibacterial agent for the target.

Question 2

BETA LACTAMS

i) what is the easy oral penicillin?
ii) which is given for staph aureus?
iii) what is given or pseudomonas?
iv) what is a type I penicillin allergy? what Ig mediates it? name three assoc symptoms
v) which type worsens with repeated exposure?

Answer 2

i) amoxicillin
ii) flucloxacillin
iii) piperacillin

iv) type I = immediate (0-72hrs post exposure)
- mediated by IgE and mast cells
- urticaria, wheeze, life threatnening

v) delated type >72hrs worsens with repeated exposure
- doesnt become immediate type

Question 3

CLARITHROMYCIN

i) what type of antibiotic is it? what does it have a similar spectrum to? which three types of bacteria is it good against
ii) name a type of bacteria it is also useful against that causes pneumonia and GU infections
iii) what is the mechanism of action? standard dose?
iv) does it have good oral bioavail? how is it metabolised? what is half life? how is it excreted?
v) name three adverse effects? name an interaction

Answer 3

i) macrolide
- similar spectrum to amoxicillin
- good against s pyogenes, pneumococcus and coliform

ii) good against cell wall deficient bacteria eg chlamidya

iii) inhibits protein synthesis in the bacterial ribosome (50s subunit)
- 500mg 12 hourly is standard dose

iv) good oral bioavail
- metabolised in the liver and metabolites are excreted in bile
- half life is 1-6 hours

v) adverse effects > nausea and diarrhoea
may alter cardiac conduction > arrhythmias
interactions > inhibits cytochrome p450

Question 4

VANCOMYCIN

i) what type of drug is it? what is the only type of bacteria it is active against? which specific bug is it useful against?
ii) what is the mechanism of action? how big is the therapeutic window? what does this mean?
iii) how orally bioavail is it? how is it metabolised? what is half life? how is it excreted?
iv) name two adverse effects
v) name two interactions

Answer 4

i) glycopeptide
- only active against gram positive bacteria
- active against resistant strains eg MRSA

ii) inhibits bacterial cell wall (peptidoglycan) formation by a different target to beta lactams
- very narrow therapeautic window (levels needed to kill the bacteria are close to toxic levels)

iii) very low oral bioavail as its a big molecule
no metabolism, 4-8hours half life and excreted in ruine

iv) nephro and ototoxic
v) interacts with other ototoxic and nephrotoxic drugs

Question 5

DOXYCYCLINE

i) what type of drug is it? which gram positives is it good against? which fram negative? what other type of bacteria is it good against? name a bacteria it is not very effective against
ii) does it have low or high c dif risk? what is its mechanism of action?
iii) how is oral bioavail? how is it metabolised? what is half life? how is it excreted (2)
iv) name two adverse effects? who should it be avoided in? (2)
v) name two interactions

Answer 5

i) tetracycline
- good against gram positive eg strep and staph and gram negs haemophilus
- also good against cell wall deficient bacteria eg chalmidya
- poor against enterbacteria and anaerobes

ii) low C diff risk
- inhibits protein synthesis in the bacterial ribosome (30s subunit)

iii) good oral bioavail, no metabolism, 6-12hr half life, excreted in urine and bile

iv) adverse > dyspepsia, photosensitivity
- avoid in pregnancy and children

v) interacts with drugs such as warfarin and digoxin > competes for protein binding

Question 6

NITROFURANTOIN

i) what is it used for? which bacteria is it good against?
ii) what is its mechanism of action?
iii) what is oral bioavail? metabolism? half life? excretion?
iv) is it safe in pregnancy? when should it be avoided?

Answer 6

i) used for lower UTIs only as too little tissue penetration anywhere else
- good against e coli

ii) complex mech of action > damages bacterial DNA
iii) good oral bioavail, not metabolised, half life 1 hour amd excreted in the urine

iv) very well tolerated
- safe in early pregnancy but avoid in late
- avoid in renal impairment > doesnt penetrate urine if eGFR is low
(no major interactions)

Question 7

ANTIBIOTIC RESISTANCE

i) name three infections that are known to be abx resistant
ii) what are the main threat to resistance? give two examples
iii) what % of ecoli is now co amox resistant?

Answer 7

i) MRSA, VRE and C dif
ii) resistance enterobacteriacea (gram negative gut bacteria) eg ecoli and K pneumoniea
iii) 46%

Question 8

CEPHALOSPORINS

i) name one? what is it used for? (3) which bacteria is it good against?
ii) what is its mechanism of action?
iii) what is oral bioavail? half life? excretion?

Answer 8

i) cefuroxime > good against gram positive and gram negative
- used for strep, staphylococcus, e coli

ii) inhibit bacterial cell wall synthesis

iii) orally bioavail > abs through GI tract and excreted in the urine
- half life 60 mins

Question 9

GENTAMICIN

i) what type of antibiotic is it? what is it used for? which bacteria is it good against?
ii) what is its mechanism of action?
iii) what is oral bioavail? metabolism? half life? excretion?
iv) mech of resistance?

Answer 9

i) aminoglycoside > used for both gram positive and negative
- some anaerobes eg c dif are resistant

ii) causes bacterial mRNA to be misread by binding to 30s subunit of bacterial ribosome

iii) needs to be given parenterally as oral/GI abs is poor
- not metabolised and excreted unchanged in urine
_ half life 2-3 hours

iv) Resistance may be due to a failure of permeation, low affinity for the bacterial ribosome or inactivation of gentamicin by microbial enzymes

Question 10

METRONIDAZOLE

i) what is it used for? which bacteria is it good against?
ii) what is its mechanism of action?
iii) what is oral bioavail? metabolism? half life? excretion?

Answer 10

i) used for anerobic bacteria eg c diff, giardia, trichomonas vaginalis, rosacea, PID
ii) DNA breakdown > cell death

iii) good oral bioavail (>90%) widely distributed
- metabolised by the liver
- half life 8 hours
- 80% excreted in urine and some by liver

Question 11

CIPROFLOXACIN

i) what type of abx is it? what bacteria does it mostly work against?
ii) what is mechanism of action?
iii) how oral bioavail is it? half life? metabolism? excretion?
iv) mechanism of resistance?

Answer 11

i) quinolone
- mostly works against gram negative - haemophilus, legionella, shigella, salmonella

ii) inhibits topoisomerases needed for bacterial replication/transcription
iii) good oral bioavail, low metabolism, half life 4-7 hours, excreted unchanged, mostly renal some faecal
iv) acquired mutations in DNA dyrase and topoisomerases