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DR Medhat MRCP

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Mechanism of action of common antibiotics<br />

- The lists below summarise the site of action of the commonly used antibiotics<br />

A. Inhibit cell wall formation :<br />

Penicillins.<br />

Cephalosporins<br />

كالم فته : synthesis B. Inhibit protein<br />

Chloramphenicol.<br />

Linozolid<br />

(bacteriostatic by stopping formation of 70s initiation complex).<br />

Aminoglycosides (cause misreading of mRNA).<br />

Macrolides (e.g. erythromycin).<br />

Fusidic acid.<br />

Tetracyclines.<br />

C. Inhibit DNA synthesis<br />

Quinolones (e.g. ciprofloxacin).<br />

Metronidazole .<br />

Sulphonamides.<br />

Trimethoprim<br />

D. Inhibit RNA synthesis<br />

Bacteriostatic<br />

Sulphonamides<br />

Trimethoprim<br />

Chloramphenicol<br />

Tetracycline<br />

Macrolids<br />

Rifampicin<br />

Summary of ttt of various infections (read on exam night) :<br />

Bactericidal<br />

Penicillins<br />

Cephalosporins<br />

Aminoglycosides<br />

Quinolones<br />

Metronidazole<br />

Rifampicin<br />

INH<br />

Nitrofurantoin<br />

Disease or organism<br />

Treatment<br />

G+ve cocci<br />

Strept.pyogens<br />

Cellulitis<br />

(strept. Pyogens)<br />

Necrotizing fasciitis (NF)<br />

(strept pyogens causes<br />

type 2 NF)<br />

Staph. Toxic shock<br />

syndrome<br />

MRSA<br />

Penicillin<br />

1 st choice : penicillin<br />

2 nd choice : flucloxacillin.<br />

If penicillin allergy : Erythromycin<br />

If failed TTT : clindamycin.<br />

Main TTT : Urgent debridement.<br />

I.v antibiotics.<br />

MSSA : Cloxacillin + clindamycin<br />

MRSA : Vancomyin /teicoplanin + clindamycin<br />

1 st line : vancomycin or teicoplanin.<br />

If not responding : add Rifampicin.<br />

If still resistant : Linozolid or tigecyclin.<br />

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