A Survey Of Commonly Used Antimicrobial Drugs

Inhibitors of Protein Synthesis

Chloramphenicol – Broad spectrum, inexpensive; small molecular size allows good penetration into tissues; known to cause aplastic anemia; used primarily as a reserve antibiotic.

Structure of Chloramphenicol

Simple structure of chloramphenicol makes it less
expensive to synthesize than to isolate from Streptomyces

Aminoglycosides – among the first antibiotics that were effective against gram-negative bacteria.

Examples:

a. Streptomycin – Toxic; now only used against mycobacteria

b. Spectinomycin – Used against penicillinase producing strains of Neisseria gonorrhoeae.

c. Neomycin – Toxic if used internally; used only in topical preparations.

d. Gentamicin - Toxic; useful against Pseudomonas infections.

e. Tobramycin – Useful in aerosol to aid the control of infections in cystic fibrosis patients.

Tetracyclines – Are said to have the broadest spectrum of all antibiotics; effective against both gram-positive and gram-negative bacteria as well as against rickettsias, mycoplasmas and chlamydias. Often used to treat urinary tract infections.

Can suppress the normal flora leading to superinfections of Candida albicans.

May cause discoloration of the teeth in children and liver damage in pregnant women.

Examples:

a. Oxytetracycline (Terramycin)
b. Chlortetracycline (Aureomycin)
c. Tetracycline
d. Semisynthetic Tetracylines (Doxycycline and Minocycline) – have longer retention in the body than the natural tetracylcines

Structure of Tetracycline

Macrolides – (Example: Erythromycin) Spectrum similar to that of penicillin G; good alternative to penicillin; Drug of choice for legionellosis and mycoplasmal pneumonia.

Newer macrolides include azithromycin and clarithromycin (Biaxin) - broader spectrum and penetrate tissues better (good against Chlamydia).

Even newer are ketolides, developed to deal with resistance. Example: telithromycin (Ketek)

Structure of Erythromycin

Lincosamides - related to macrolides, lincomycin was the first to be discovered (a naturally occurring antibiotic, not synthetic!) and have similar effects.

Clindamycin is a newer semi-synthetic version, useful against gram-positive cocci (including anaerobes), with the exception of enterococci; also active against Chlamydia trachomatis, Chlamydophila pneumoniae, Legionella pneumophila and other Legionella spp, Corynebacterium diphtheriae, Campylobacter, Treponema pallidum, Bacteroides sp., and Borrelia burgdorferi.

Streptogramins - useful against vancomycin-resistant organisms.

Syncercid - combination of quinupristin and dalfopristin, block protein synthesis.

Effective against a broad range of gram-positive organisms but expensive and has a lot of side effects

.

Oxazolidinones - also useful against vancomycin resistance, especially enterococci that are resistant to syncercid.

Totally synthetic, may slow development of of resistance.

Example: linezolid (Zyvox)