Antimicrobial agents 1 Flashcards by Georgia Leggett

What is the broad mechanism of action of beta lactams?

Inhibition of cell wall synthesis

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What is the broad mechanism of action of glycopeptide antibiotics?

Inhibition of cell wall synthesis
Bind to peptide crosslink sticking out of pep glycol precursor, prevent bond formation

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What 3 groups of antibiotics are classified as beta lactams?

Penicillins
Cephalosporins
Carbapenems

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Name 2 glycopeptide antibiotics

Vancomycin
Teicoplanin

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Describe the mechanism of action of beta lactams

Inactivates transpeptidase enzyme that forms X-links during cell wall synth.
Resulting cell wall is weak, so bacteria lyse because of osmotic pressure.

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What bacteria is penicillin active against?

+ve

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What bacteria is amoxicillin active against?

BS: +ve, enterococci + gm -ve

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Is streptococci gram pos or neg?

+ve

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Which beta lactam antibiotic is effective against pseudomonas?

Piperacillin-Tazobactam
(Tazocin)

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How can beta lactam resistance be overcome?

Include a B-lactamase inhibitor
E.g. Amoxicllin + Clavulanic acid (co-amoxiclav)
Piperacillin + Tazobactam (Tazocin)

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Is pseudomonas gram pos or gram neg?

-ve bacilli
(Pseudo”moan”as ‘moan’ = negative)

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Is neisseria meningitis gram pos or gram neg?

-ve cocci
(Neisseria starts with N = negative)

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Recall 3 antibiotics associated with C. difficile

Ceftriaxone (cephalosporin)
Clindamycin (lincomycin)
Ciprofloxacin (fluoroquinolone)

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Which beta lactam antibiotics are stable to ESBL organisms?

Carbapenems

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Recall 3 cautions of beta lactam antibiotic

Excreted renally: reduce dose if renal impairment
Short half life: multiple doses spaced equally required
Cross-allergenic (penicillins 10% X-reactivity with cephalosporins/ carbapenems)

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What type of bacteria are glycopeptides effective against?

+ve only
Are large molecules so can’t penetrate -ve outer cell wall

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What infection are glycopeptides particularly useful for?

MRSA

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What is a caution of glycopeptide antibiotics?

Nephrotoxic
Monitor levels to prevent accumulation

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Recall the broad mechanism of action of glycopeptide antibiotics

Prevent peptide X-links in cell wall

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What type of bacteria are aminoglycoside antibiotics effective against?
Recall MOA of aminoglycosides

-ve
Bind to 30s ribosomal subunit, preventing elongation of polypeptide chain
No anaerobic activity

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Recall 2 examples of aminoglycoside antibiotics

Gentamicin (effective in P. aeruginosa)
Amikacin

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Recall 2 toxicities of aminoglycosides

Ototoxicity
Nephrotoxicity

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What type of bacteria are macrolides effective against?

+ve
Bind to 50s subunit of ribosomes

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What are macrolides particularly useful for? What else are they active against?

Mild staph or strep infections in penicillin allergic
Campylobacter sp + legionella pneumophila

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Recall 3 macrolide antibiotics

Azithromycin Clarithromycin Erythromycin

What type of bacteria are tetracylines effective against?

BS Intracellular pathogens e.g. Chalmydiae, Rickettsiae, Mycoplasma

Recall a class of antibiotic you should never give to children or pregnant women

Tetracyclines as TERATOGENIC, deposit in growing bones

Recall one side effect of tetracycline antibiotics

Light-sensitive rash Avoid sun

Recall the broad mechanism of action of tetracyclines

Bind to 30s subunit of ribosomes

What type of bacteria is chloramphenicol effective against? What may chloramphenicol be used for?

V Broad Spectrum Eye drops

Why is chloramphenicol rarely used?

Risk of aplastic anaemia + grey baby syndrome in neonates due to inability to metabolise drug

Recall the broad mechanism of action of chloramphenicol

Binds 50s subunit of ribosomes Inhibits formation of peptide bonds during translation

Recall the broad mechanism of action of oxazolidinones

Binds 23s + 50s subunit of ribosomes to prevent 70s subunit formation

Recall two types of bacteria that oxazolidinones are particularly active against

Highly active against gram +ve, inc: MRSA + VRE

Recall an example of oxazolidinones

Linezolid

Recall one potential side effect of oxazolidinones

Thrombocytopaenia (+ expensive) (+ can cause serotonin syndrome)

Recall the MOA of fluoroquinolones

Act on alpha subunit of DNA gyrase Broad activity, esp. vs -ve inc. P aeruginosa Levo + Moxi have activity against +ve and intracellular e.g. Chlamydia

Recall 4 uses of fluoroquinolones

UTI Pneumonia Atypical pneumonia Bacterial gastroenteritis

Recall 3 examples of fluoroquinolone antibiotics

Ciprofloxacin Levofloxacin Moxifloxacin

Give an example of a nitromidazole antibiotic

Metronidazole

Recall types of organisms that metronidazole is effective against

Anaerobes Protozoa e.g. Giardia

When should metronidazole be taken?

Right after visiting the toilet as it sits in bladder

Recall the broad mechanism of action of rifampicin

Inhibits RNA polymerase

Recall the main use of rifampicin

Recall one side effect of rifampicin

Turns secretions orange

Recall one condition of rifampicin prescription

Never prescribe alone as resistance develops very quickly

Name 2 cell membrane toxins. How do their activity differ from other antibiotics?

Daptomycin. +ve. Limited by surfactant, not good in lungs. Colistin. -ve. Nephrotoxic, reserved for MR bacteria Work when bacteria are NOT active.

What is daptomycin licensed for the treatment of?

MRSA VRE

Recall the 2 classes of antibiotic that inhibit folate metabolism

Sulphonamides Diaminopyrimidines e.g. Trimethoprim

What does Trimethoprim combined with sulfamethoxazole form? What is this used for?

Septrin (co-trimazole) PCP Elderly- doesn't exacerbate C diff

What is the main use of trimethoprim alone?

Uncomplicated UTI

What are the 4 main mechanisms of resistance

1. Inactivation- B latamases 2. Altered target (abx no longer binds - important in MRSA where bacteria change PBP, + in protein-synthesis inhibitors where binding of ribosome subunit is prevented) 3. Reduced accumulation (most important in gram -ve: either due to efflux or to reduced uptake) 4. Bypass (important for folate inhibitors: bacteria can change the enzyme they use)

Name 2 classes of abx that inhibit DNA synthesis

Fluoroquinolones Nirtromidazoles

Which bacteria typically forms "gram pos cocci in clusters"?

Staphylococcus

Which bacteria typically forms "gram pos cocci in chains"?

Streptococcus Strep sounds like 'stripe' = chain

What gram stain status are enterococci?

+ve ("Enter-o-coccus" = like letting someone in, +ve thing to do)

Is haemophilus gram pos or neg?

-ve Ha"emo"philus - emo = -ve

Is listeria gram pos or neg?

+ve Lister = good man = +ve

How do gram positive and negative bacteria differ in their cell walls?

+ve: THICK peptidoglycan -ve: THIN peptidoglycan, have outer membrane

Against which cells are b-lactams ineffective against?

Those lacking pep wall: Chlamydia + Mycoplasma Those not metabolically active/ dividing: biofilms/ abscesses/ prostheses

What is transpeptidase also known as?

Penicillin binding protein

Which penicillin is penicillinase stable? Against which bacteria does this allow use for compared to other penicillins?

Flucloxacillin Use against S aureus

Describe the components of Co-amoxiclav

Clauvanic acid is a b-lactamase inhibitor allows Amoxicillin to retain activity

Give examples of each generation of cephalosporin. How do they differ?

Increasing activity against -ve bacilli 1: Cephalexin 2: Cefuroxime 3: Cefotaxime, Ceftriaxone, Ceftazidime

What is ceftazidime most commonly used for?

Anti-pseudomonas

Which enzymes confer resistance to Cephalosporins? What drug may be used instead?

ESBL Rx: Carbapenem e.g. Meropenem

Give 3 examples of Carbapenems

Meropenem Imipenem Ertapenem

Which emerging enzymes would confer resistance to Meropenem?

Carbapenemase

How do B lactase interact with the blood brain barrier?

Intact: DONT cross (non-inflamed meninges) Meningitis: cross BBB as high dose used + inflamed meninges

Why are B lactams more preferable to glycopeptides?

Glycopeptides are slowly bactericidal

What can Vancomycin PO be used to treat?

Serious C. difficile

2 examples of glycopeptides

Vancomycin Teicoplanin

Give 5 classes of protein synthesis inhibitor antibiotics

Aminoglycosides Tetracyclines Macrolides Chloramphenicol Oxazolidinones

2 side effects of fluoroquinolones

Tendonitis Lowers seizure threshold

What is a related class of compounds to Nitroimidazoles?

Nitrofurans- Nitrofurantoin used in simple UTIs

Why does DH need to be considered when prescribing Rifampicin?

Enzyme inducer Increases rate of metabolism of drugs metabolised by liver

How can Streptococcus pneumoniae resistance be overcome?

Mutation: Becomes step-wise resistant with altered PBP Overcome with high dose if low level resistance

Why has there been tx failure reported with B lactamase inhibitors?

In ESBL +ve bacteria Traditional inhibitors don't work against all enzymes

What is the mechanism of resistance to macrolides?

Altered target: ribosomal methylation encoded by ERM gene Ribosome which macrolide binds to is altered, no longer binds

What antibiotic should you avoid if you see macrolide resistance?

Clindamycin (related to macrolides, so may be resistance)