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Infectious Diseases > Use of antibiotics > Flashcards

Use of antibiotics Flashcards

1
Q

what are the basic pharmacokinetic parameters?

what does AUC mean

Cmax

A
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2
Q

what is meant by pharmacodynamics?

A

this is the relationship between antibiotic concentration and antibacterial effect

this is different from pharmacokinetics (which is drug dosing and drug concentration at the site of action)

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3
Q

which antibiotics are associated with concentration dependent killing?

A

aminoglycosides

quinolones

aim for high peaks and large AUC

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4
Q

what are some non concentration-dependent antibiotics?

A

beta lactams

beyond a certain point, there is no benefit in increasing the concentration, and so the goal of dosing is to maximise the time of exposure to the drug (esp time above MIC)

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5
Q

which are the bacteriostatic antibiotics?

A

tetracyclines and erythromycon are both bacteriostatic antibiotics and they are best to avoid during serious, difficult-to-treat infections such as IE

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6
Q

what are some of the important gaps in the meropenem spectrum?

A

stenotrophomonas

enterobacter faecium

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7
Q

What are the ESCAPPM bugs?

what type of bug?

A

these are Gram negative rods

NOTE: THIS CLEARLY EXCLUDE ENTEROCOCCUS (GRAM POS COCCI)

Enterobacter

Serratia

Citrobacter

Aeromonas

Proteus

Providencia

Morganella

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8
Q

which of the beta lactams are most associated with hepatitis?

A

fluclox and diclox

augmentin also, but in that case it’s thought to be the clavulanic acid, rather than the methicillin addition to the beta lactam

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9
Q

what are the three aminoglycosides?

what is their mechanism of action?

what do they cover? (which bugs)

A
  1. gentamicin
  2. amikacin
  3. tobramycin

they inhibit protein synthesis at ribosomes

Gram negative aerobic cover ONLY

all of them have adverse kidney (reversible) and hearing/vestibular (irreversible) issues

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10
Q

what’s more important in aminoglycosides, high peak or large AUC?

A

Dr Munckhof did not elaborate, but the answer is large AUC, but only just

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11
Q

how do the quinolones work, and what are some of their names?>

A

ciprofloxacin

moxifloxacin

they work by inhibiting DNA gyrase

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12
Q

what is the spectrum of the newer quinolones?

A
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13
Q

what are the major ADR to quinolones?

is there any special info about when to give these meds/what not to give them WITH?

any drug interactions?

A

tremor, headaches (esp elderly)

QT prolongation

maybe abn cartilage in kids

N/V/rash

you should give them at least 2 hours apart from calcium/antacids/iron tablets

they interact with phenytoin and theophylline

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14
Q

what are the macrolides, and what is their mechanism of action?

are they bacteriocidal or static?

what is their main spectrum?

A

they are erythromycin, roxithromycin, azithromycin and clarithromycin

they inhibit protein synthesis at ribosomes

  • they are bacteriostatic
  • work against MSSA, strep (so, gram pos), works against aerobic gram negs, not really against anaerobes

their main spectrum is legionella, mycoplasma, chlamydia, diptheria pertussis

major indication: atypical pneumonias, pertussis, chlamydial genital infections, atypical mycobact infections

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15
Q

what are the lincosamides?

what is their use and mechanism of action?

A

they are clindamycin and lincomycin

useful against anaerobes and gram pos cocci (staph and strep BUT NOT ENTEROCOCCI)

they work by inhibiting bacterial ribosomal protein synthesis

they cover staph well, including MRSA

they have good bone and joint penetration

cause N/V

c diff is a big deal

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16
Q

what are the tetracyclines? what is their mechanism of action

what is their major indication?

A

doxycycline in the main one we use

they work by binding to the bacterial ribosome and stopping binding between tRNA and mRNA

they have good activity against mycoplasma, chlamydia, Q fever

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17
Q

What are the nitroimidazole?

what are their mechanism of action?

what do they cover best?

A

metronidazole, tinidazole

they cover ONLY anaerobes (and parasites like giardia)

they interact with bacterial nucleic acid and screw up DNA synth

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18
Q

what are the indications for bactrim? how do these drugs work?

ADRs?

A

they both work on the folate synthesis pathway

  • the addition of the sulpha group rarely adds efficacy, as most of the anti-microbial activity seems to come from the trimethoprim component

the sulpha component causes rash and haematological abnormalities

there are some indications for both - PJP and stenotrophomonas, for example

19
Q

What is the role of colisitin?

how does it work

what is its spectrum?

A

this is a gram negative agent

very difficult to dose and major toxicity is the nephrotoxicity

it works like a detergent. it is both hydrophilic and hydrophobic (in parts)

it gets in the gram neg bacteria plasma membrane, and displaces some of the proteins, like LPS, and leads to cells break down

20
Q

what are the glycopeptides?

what is their mechanism of action?

major ADR?

A

vancomycin is the major drug of this class

needs to be monitored

Good Gram POS coverage, but no gram neg and no anaerobic cover

need to watch for red man syndrome

it works by blocking the cross linking bonds in the cell wall synthesis of bacteria

the other glycopeptide is teicoplanin

  • this has similar coverage, but also can treat some VRE (the VanB subtype - most common in Australia)
21
Q

what is the oral treatment of hospital acquired MRSA?

A

this is tricky

one needs to use dual agents, to prevent development of resistance

the best combination is rifampicin and fusidic acid, but this has a significant side effect profile, including nausea, hepatitis and the red urine/tears

rif also has lots of p450 interactions

22
Q

what is the oral treatment for CA-MRSA?

A

usually these have a strange resistance profile

oral options usually include clindamycin and cotrimoxazole

the IV would be vancomycin

23
Q

what are the glycylcyclines?

what is their benefit?

A

tigecycline

broad spectrum of action - gram neg and gram pos, but there are gaps in the coverage - no good against pseudomonas or proteus

they are a new class of modified tetracycline (which disturb bacterial DNA synthesis)

they manage to evade bacterial efflux and ribosomal resistance mechanisms (which was a problem for tetracyclines)

24
Q

what are the oxazolidinones?

how do they work?

what do they work on?

major ADRs?

A

these are a new class of drugs

linezolid is within this class

they have a unique mechanism of action, working on the ribosome preventing bacterial protein synthesis

they are good against GRAM POS, but because of cost, we only really use it for bad VRE, VISA or VRSA

they have no useful activity against gram neg or anaerobes

major ADR is myelosuppression

there is also stories of peripheral neuropathy

25
Q

what are the glycolipopeptide class?

what do they work against?

what are we allowed to use them for?

any blood tests you need to do regularly (while patients are on it?)

A

this class includes daptomycin

they are bacterial cell membrane destabilisers

this has an excellent activity against most Gram pos, but nothing good against Gram neg or anaerobes

because of cost, we use them for VISA/VRE

side effect is myositis

also small incidence of eosinophilic pneumonia

if giving this to people you need to monitor serum cK

26
Q

what is amphotericin?

what are the major preparations, and what are the major risks of this drug?

what is the spectrum?

how does it work?

A

pretty broad spectrum - includes moulds (aspergillus) and yeasts (candida and cryptococcus)

renal toxicity is a major issue

liposomal preparation has less renal toxicity, but is 15 times more costly!

it works by binding to ergosterol and disrupts the fungal cell membrane and creates a cross-membrane channel

27
Q

what is fluconazole?

what is its spectrum?

what is its mech of action?

A

fluconazole is the main drug.

the spectrum is mostly YEASTS - cryptococcus and candida particularly (not mouldy ol’ aspergillus)

they work by binding to the fungal cyto P450 and preventing creation of ergosterol which is essential for cell wall sythesis

it is more common to have resistance if patient has been on fluconazole in the past

major ADRs are related to p450 interactions

28
Q

aside from fluconzaole there are some newer azole drugs.

what are they, what are their spectrum and interactions?

do you have to do any special therapeutic monitoring with these drugs?

A

voriconazole and posaconazole are the two main ones

they are more expensive

they have a broadened spectrum and also cover some moulds, incl aspergillus

they still have p450 interactions which are a big deal

it is important to monitor the levels of voriconazole

29
Q

what are the echinocandins?

how do they work

what is their spectrum?

A

caspofungin is the main one in Australia

given IV

the spectrum is reasonably narrow - candida (a yeast) and aspergillus (a mould)

but no activity against other moulds

its benefit is that it is rarely toxic

works by inhibiting beta-glucan-sythase, leading to loss of cell wall integrity

30
Q

what is the most important parameter for prescribing of beta lactams?

a. peak concentration/MIC ratio
b. AUC
c. AUC/MIC ratio
d. time above MIC
e. both AUC/mic ratio and peak concentration/MIC ratio

A

the answer with beta lactams is really just about time above the MIC

the most important thing is to keep the blood levels above MIC. There is a plateau around 3x MIC, above which treatment does not provide benefit

31
Q
A
32
Q

see image

A

diabetic foot infections are usually mixed infections, including staph aureus, strep pyogenes, some gram negs, some anaerobes

the main thing with diabetic foot ulcers is to make sure that your antibiotics have some anaerobic coverage

(recall that bugs can be defined as: gram pos aerobes, gram neg aerobes, anaerobes and atypicals)

the best answer is B, which will cover anaerobes well

33
Q

see image

A

this is important because there has been a historical thinking that group a strep isn’t covered by fluclox, which is wrong.

another option would be cephazolin (but not asked here because that would create redundancy)

the answer is D

however, in the future there is a real possibility that first line will switch to vancomycin, once resistances get worse

34
Q

see image

A

this is about a 12 year old that progresses on oral amoxy

there are right basal CXR changes

in this setting (progression on orals), we should look at IV treatment.

The best option would be Iv penicillin and oral roxi/doxy

however, that isn’t an option, so instead IV penicillin

(IV cefotaxime is too broad)

35
Q

if you had a neutropenic patient with sepsis, normal regimen is pip/taz

is there any rationale for the addition of gentamicin?

A

the PAH ID/haem team argues that gentamicin should be given to cover for ESCAPPM, as up to 30% of hosp acquired infections are related to these

and the thinking is that neutropenics are in and out of hospital all the time

this is also the reason for the changing to ceftazadime in many haem units

the importance of gram neg coverage in neutropenic sepsis = must cover pseudomonas! (can kill overnight)

36
Q

see image

A

what is the treatment post surgically?

we need to cover pneumococci, haemophilis and meningococci

in this day and age, if we see something that represents pneumococci or recent sinus/neuro surgery, you MUST add vancomycin to ceftriaxone

there is also a strong argument for steroids before antibiotics (based on eTG)

37
Q

what is the prophylaxis for meningococcus meningitis?

what about pregnancy etc?

A

if non preggo:

  1. rifampicin
  2. ciprofloxacin
  3. ceftriaxone

if preggo:

  • ceftriaxone (IM is fine)
38
Q

see image

A

ct is a likely brain abscess

  • need to cover anaerobes, gram pos mouth flora

aciclovir isn’t necessary - not HSV

rifampicin not a strong treatment agent

vanco and rif don’t have anaerobe coverage

the real question is B vs D

the reason for B (the answer) is that the penicillin gives coverage of millerei. Vancomycin might be useful in the future, once CA-MRSA becomes an even bigger problem

39
Q

see image

A

all except CTX have decent anaerobe cover

cipro also has poor anaerobic coverage

chloramphenicol isn’t used much, but had very good anaerobe cover

40
Q

see image

A

the key to this question is recognising the anaerobic nature of bacteroides fragilis

the next step is to identify which of the antibiotic options has anaerobic coverage

the answer is b - clindamycin

41
Q

which of moxifloxacin or ciprofloxacin has better pseudomonas coverage?

A

cipro has best pseudo cover

moxi loses some pseudo coverage to gain gram pos cover

42
Q
A

pseudomonas coverage is an important concept to understand

CTX has no pseudomonas coverage

this is VITAL to know

43
Q
A

Infectious Diseases (13 decks)

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