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Flashcards in 1 - Introduction to antibacterial agents Deck (56):
1

Antibiotics

Chemical products of microbes that inhibit or kill other organisms

2

Antimicrobial agents

Antibact/fungal/viral
Antibiotics
Synthetic compound with similar effect
Semi-synthetic i.e. modified from antibiotics

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Bacteriastatic Definition

Inhibit bacterial growth - protein synthesis inhibitors

4

Bactericidal Definition

Kill bacteria - cell wall-active agents

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Minimum inhibitory concentration

Minimum concentration of antibiotic at which visible growth is inhibited

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Synergism

Activity of two microbials given together is greater than the sum of their activity if given separately

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Antagonism

One agent diminishes the activity of another

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Indifference

Activity unaffected by another agent

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Example of synergism in clinical practice

B-lactam/aminoglycoside combintaion therapy of streptococcal endocarditis

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Targets of antibiotics

Cell wall
Protein synthesis
DNA synthesis
RNA synthesis
Plasma membrane

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Bacterial cell wall contains...

Peptidoglycan

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Describe peptidoglycan

Major component of cell wall
Both gram-+ve and gram--ve
Polymer of glucose derivatives, N-acetyl muramic acid (NAM) & N-acetyl glucosamine (NAG)

No cell wall in animal cells = selective toxicity

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What is selective toxicity

Destroy bacterial cells and not human cells

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Cell wall synthesis inhibitors

B-lactams
Glycopeptides
Cycloserine (anti-tuberculous agent)

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B-lactam antibiotics what are they?

First true antibiotics = penicillins
All contain B-lactam ring three carbons in a ring with nitrogen.

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B-lactam antibiotics how do they work

interfere with function of penicillin binding proteins, which are transpeptidases enzymes involved in the petideoglycan cross-linking

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Penicillin vs enterobacteriaceae

Ampicillin

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Anti-staphyolococcal penicillin

Meticillin

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Penicillin main examples

Amoxicillin - relatively narrow spectrum

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Cephalosporins example

Cefuroxime - broad spectrum

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Carbapenems examples

Meropenem, imipenem
Extremely broad spectrum

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Monobactams

Aztreonam - gram-ive activity only

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Glycopeptides

Vancomycin, teicoplanin
Large molecules bind directly to terminal D-alanyl-D-alanine on NAM pentapeptides.
Inhibits transpeptidase binding.
Gram-positive activity only as cannot penetrate gram--ve outer membrane

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Aminoglycosides

Gentamicin, amikacin
Bind to 30S ribosomal unit (small)
Do not understand mechanism
Can cause nephrotoxicity so careful when dealing with people with AKI

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Protein synthesis inhibitors

Macrolides, lincosamides, streptogramins

e.g. erythromycin, clarithromycin (macro)

clindamycin (linco) bind to 50S ribosomal subunit, block tunnel exit, inhibit protein elongation

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Tetracyclines

Tetracycline, doxytetracycline
Bind to 30S ribosomal unit and inhibit RNA translation

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Oxazolidinones

Linezolid
Inhibit initiation of protein synthesis binds to 50S

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Trimethoprim and sulfonamides

Inhibit folate synthesis, which is purine synthesis precursor.

Trimethoprim e.g. dihydrofolate reductase

Sulfonamides e.g. dihydropteroate synthetase

Combined as co-trimoxazole

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Quinolones and fluoroquinolones

Inhibit one or more of two related enzymes

e.g. nalidixic acid, ciprofloxacin, levofloxacin

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Rifampicin

RNA poly inhibitor
Prevents mRNA synthesis

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Plasma membrane agents

Colistin (gram--ve) - last resort antibiotic - but resistance even goes this far recently.
Daptomycin (gram-+ve) cyclic lipopeptides destroy cell membrane

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Adverse effects of all drugs

Nausea etc
Infusion reactions
Allergic reactions

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Generation of antibiotic resistant - adverse effects

Selection of resistant strains in patient
Preferential colonisation on exposure to resistant stains

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Fungal infection adverse effects

Superficial and invasive candidasis

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Another adverse effect of antibiotics

C. diff

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Aminoglycosides adverse effects

Reversible renal impairment on accumulation
Irreversible ototoxicity
Need drug monitoring via blood tests to check for accumulation

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B-lactams adverse effects

1-10% general rash
0.01% anaphylaxis

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Linezolid adverse effects

Bone marrow depression

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B-lactams and allergy

Intolerance (nausea, diarrhoea etc)
Minor allergic reactions (non-severe skin rash)
Severe allergic reactions (anaphylaxis, urticaria, angio-oedema, bronchospasm, severe skin reaction (Stevens-Johnson syndrome)

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Which drugs are safe to use in people with penicillin allergies?

Cephalosporins, Carbapenems in patients with non-severe penicillin allergy
Aztreonam in patients with any penicillin allergy

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Common precipitating antibiotics for C.diff

4Cs:
Co-amoxiclav
Cephalosporins
Ciprofloxacin
Clindamycin

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Less common precipitating antibiotics for C.diff

Benzylpenicillin, aminoglycosides, glycopeptides.
Piperacillin-tazobactam
Could be any antibiotics however

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Key antibiotic/bacteria combo
Flucloxacillin

Staph aureus (not MRSA)

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Key antibiotic/bacteria combo
Benzylpenicillin

Strep pyogenes

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Key antibiotic/bacteria combo
Cephalosporins

(avoid in elderly)
Gram--ve bacilli

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Key antibiotic/bacteria combo
Metronidazole

Anaerobes

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Key antibiotic/bacteria combo
Vancomycin

Gram-positives (MRSA)

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Key antibiotic/bacteria combo
Meropenem

Most clinically-relevant bacteria

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Key antibiotic/bacteria combo
Colistin

Last option for multi-resistant gram--ves

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in vivo efficacy for CSF as site of action

B-lactams = good
Aminoglycosides + vancomycin = poor

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In vivo efficacy for urine as site of action

B-lactins = good
Trimethoprim = good
MLS antibiotics = poor

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Main determinant of bacterial killing is:

the factor by which concentration exceeds the MIC = minimal inhibitory concentration

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Which drugs are administered intermittently to achieve high peaks?

Aminoglycosides

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Which drugs are administered frequently to maintain a high level?

B-lactams

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What effects pharmacodynamic concentrations

Concentration and time dependent

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Combination therapy benefits

Increase efficacy
Provides adequately broad spectrum
Reduce resistance

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