Classes of antibiotics and their Spectrum of Activity

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