Classes of Antibiotics and their Spectrum of Activity
19th century. In 1929, Sir Alexander Fleming accidentally discovered the antibacterial properties of penicillin by destroying the staphylococcus in culture plate; this is broadly cited in modern antibiotic era. Chain and Florey followed up this observation in 1939 and later penicillin was clinically used during 1941. In 1942, Waksman proposed the search of actinomycetes and discovered streptomycin in 1944. Later, the advance in medicinal chemistry produced synthetic and semisynthetic agents.
The ability of drug with all ranges (gram positive and gram negative) of antibiotic action, chloramphenicol, and tetracycline, to antagonize numerous pathogens have resulted mention as broad-spectrum antibiotics. Many of the broad-spectrum antibiotics are active only at high concentration. Some drugs are primarily static and they may exert cidal action at high concentration (e.g. sulphonamides, erythromycin, nitrofu- rantoin, etc). The bacteriostatic agents are those that interfere with the growth or replication of microorganisms, but does not kill it. The bactericidal drugs are those that kills the microorganisms. Concentration of drugs at the site of infection is an important factor for the therapeutic effect in case of antimicrobials. The classes of antibiotics and their spectrum of activity is detailed in below
Classes of antibiotics and their Spectrum of Activity
| Class of Antibiotics | Name of the Drugs | Susceptible Organism |
| Natural penicillins | Penicillin G and V | Gram positive bacteria streptococci except viridians. Gram positive Bacilli, i.e. B. anthracis, Corynebacterium diphtheriae, and all Clostridia |
| Semisynthetic penicillins | Oxacillin | Penicillinase-resistant
|
| Ampicillin | Broad spectrum. It is active against all organisms, which are sensitive to penicillin G and many gram-negative organisms, i.e. Haemophilus infl uenzae, Escherichia coli, Proteus, Solmonella, and Shigella | |
| Amoxycillin | Broad spectrum antibacterial action with penicillinase inhibitor. It is less active against Shigella and H. infl uenzae | |
| Aztreonam | Pseudomonas and gram-negative organism
|
|
| Cephalosporins | Cefazolin | It is active against all organisms and sensitive to penicillin, i.e. Streptococci, Gonococci, Meningococci, C. diphtheriae, H. infl uenzae, Clostridia, and Actinomycetes. Highly active against Klebsiella and E. coli |
| Cephalothin | Similar in spectrum to Cefazolin, but less active against penicillinase producing Staphylococci and H. infl uenzae. Parentral administration produces broad spectrum action | |
| Cefotaxime | Potent action against aerobic gram negative and some gram positive, not active against anaerobes; Staphylococcus aureus and Pseudomonas aeruginosa | |
| Glycopeptide
antibiotics |
Bacitracin | Gram-positive organisms of both cocci and Bacilli |
| Vancomycin | Gram-positive bacteria. It is useful in case of methicillin resistant Staphylococcus aureus, Streptococcus viridans, and Enterococcus | |
| Polymyxin | Gram negative, including Pseudomonas species | |
| Antimycobacterial
antibiotics |
Isonoazid, Ethambutol | Mycobacterium species |
| Inhibitors of protein
synthesis |
Chloramphenicol | Broad spectrum |
| Aminoglycosides | Streptomycin | Broad spectrum, including Mycobacterium species. Primarily active against aerobic gram-negative bacilli. |
| Neomycin | Broad spectrum activity
|
|
| Gentamycin | Broad spectrum, including Pseudomonas species. Ineffective against Mycobacteriumtuberculosis, Streptococcus pyogens, and Pneumoniae | |
| Tetracyclines | Tetracycline,
oxytetracycline, doxycycline, minocycline, and clortetracyclin |
All types of pathogens except virus and fungi. Broad spectrum including chlamydia, spirochetes, and rickettsia. Mycoplasma and Actinomyces are moderately sensitive. |
| Macrolides | Erythromycin | Gram-positive bacteria, highly active against Str. pyogens, Neisseria gonorrhoeae, Clostridia, C. diphtheriae, and Listera |
| Clarithromycin | Similar to erythromycin, in addition M. avium complex. More active against gram-positive cocci, Moraxella, Legionella, Mycoplasma pneumonea, and H. pylori | |
| Azithromycin | Less effective in gram-positive cocci. Highly active against respiratory pathogens, i.e. Mycoplasma, Chlamydia, Moraxella, Pneumoniae, and Legionella | |
| Streptogramins | Quinupristin & dalfopristin | Vancomycin resistant, methicillin resistant gram-positive bacteria |
| Oxazolidindione | Linezolid | It is active against methicillin resistant Staphylococcus aureus. Cidal to Streptococci, Pnemococci, and Bacteriodes Fragilis |
| Quinolones & fluoroquinolones | Nalidixic acid, gatifloxacin, pefloxacin, norfloxacin, ciprofloxacin, etc | Most susceptible are gram negative bacilli. At high concentration gram positive bacteria highly susceptible bacteria are E. coli, Klebsiella pnemoniae, Enterobacter, Solmonella typhi, Shigella proteus, Camphylobacter jejuni, Vibrio cholerae, Pseudomonas auruginosa, Brucella, Listeria, and B. anthracis are little Susceptible |
| Sulphonamides | Cotrimoxazole and
other sulpha drugs |
Broad spectrum. Primarily bacteriostatic
|
| Nucleoside and nonneucleoside analogues | Acyclovir, Ganciclovir, ribavirin, lamivudine | Herpes virus |
| Cidofovir | Cytomegalo virus | |
| Tricyclic amines | Amantidine, Rimantidine | Influnzea virus |
| 8-Hydroxy quinolones | Quinidochlor | Malarial parasites
|
| Nitrimidazoles | Metronidazole and tinidazole | Broad spectrum action against protozoa, trichomoniasis, and Giardiasis infections |
| Benzimidazole | Albendazole, mebendazole | Enterobias, Trichuris infestations |
| Polyenes | Amphotericin B | Systemic fungal infection, active against wide range of yeasts and fungi, i.e. Candida albicans, Histoplasma capsulatum, Blastomyces dermatitidis, Cryptococcus neoformans, Aspergillus, sporothrix, and Torulopsis |
| Azole derivatives | Ketaconazole, clotrimaxazole, miconazole | Systemic fungal infection, Topical infection. Imidazole and triazole has broad spectrum antifungal action covering dermatophytes, Candida, nocardia, some gram positive and anerobic bacteria, i.e. Staphylococcus aureus, Bacillus fragilis, and leishmania |
| Allylamines | Terbinafi ne, Naftidine | Resistant organisms for azoles
|
| Heterocyclic benzofuran | Griseofulvin | Most dermatophytes of skin fungal infection but not against Candida |
- Classification of Drugs in Nepal
- Timeline of Antibiotics
- How to Learn Drug’s Name and Classification
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