Antibiotics

In common usage, an antibiotic (from the Ancient Greek: ἀντί – anti, "against", and βίος – bios, "life") is a substance or compound that kills or inhibits the growth of bacteria. Antibiotics belong to the broader group of antimicrobial compounds, used to treat infections caused by microorganisms, including fungi and protozoa.

The term "antibiotic" was coined by Selman Waksman in 1942 to describe any substance produced by a microorganism that is antagonistic to the growth of other microorganisms in high dilution. This original definition excluded naturally occurring substances that kill bacteria but are not produced by microorganisms (such as gastric juice and hydrogen peroxide) and also excluded synthetic antibacterial compounds such as the sulfonamides. Many antibiotics are relatively small molecules with a molecular weight less than 2000 Da.

With advances in medicinal chemistry, most antibiotics are now semisynthetic — modified chemically from original compounds found in nature, as is the case with beta-lactams (which include the penicillins, produced by fungi in the genus Penicillium, the cephalosporins, and the carbapenems). Some antibiotics are still produced and isolated from living organisms, such as the aminoglycosides, and others have been created through purely synthetic means: the sulfonamides, the quinolones, and the oxazolidinones. In addition to this origin-based classification into natural, semisynthetic, and synthetic, antibiotics may be divided into two broad groups according to their effect on microorganisms: those that kill bacteria are bactericidal agents, while those that only impair bacterial growth are known as bacteriostatic agents.

Antibiotic resistance

The emergence of antibiotic resistance is an evolutionary process that is based on selection for organisms that have enhanced ability to survive doses of antibiotics that would have previously been lethal. Antibiotics like Penicillin and Erythromycin which used to be one-time miracle cures are now less effective because bacteria have become more resistant. Antibiotics themselves act as a selective pressure which allows the growth of resistant bacteria within a population and inhibits susceptible bacteria. Antibiotic selection of pre-existing antibiotic resistant mutants within bacterial populations was demonstrated in 1943 by the Luria-Delbrück experiment. Survival of bacteria often results from an inheritable resistance. Any antibiotic resistance may impose a biological cost and the spread of antibiotic resistant bacteria may be hampered by the reduced fitness associated with the resistance which proves disadvantageous for survival of the bacteria when antibiotic is not present. Additional mutations, however, may compensate for this fitness cost and aids the survival of these bacteria.

The underlying molecular mechanisms leading to antibiotic resistance can vary. Intrinsic resistance may naturally occur as a result of the bacteria's genetic makeup. The bacterial chromosome may fail to encode a protein which the antibiotic targets. Acquired resistance results from a mutation in the bacterial chromosome or the acquisition of extra-chromosomal DNA. Antibiotic-producing bacteria have evolved resistance mechanisms which have been shown to be similar to and may have been transferred to antibiotic resistant strains. The spread of antibiotic resistance mechanisms occurs through vertical transmission of inherited mutations from previous generations and genetic recombination of DNA by horizontal genetic exchange. Antibiotic resistance exchanged between different bacteria by plasmids that carry genes which encode antibiotic resistance which may result in co-resistance to multiple antibiotics. These plasmids can carry different genes with diverse resistance mechanisms to unrelated antibiotics but because they are located on the same plasmid multiple antibiotic resistance to more than one antibiotic is transferred. Alternatively, cross-resistance to other antibiotics within the bacteria results when the same resistance mechanism is responsible for resistance to more than one antibiotic is selected for.

Antibiotics by class
Generic name	Brand names	Common uses	Possible side effects	Mechanism of action
Aminoglycosides
Amikacin	Amikin	Infections caused by Gram-negative bacteria, such as Escherichia coli and Klebsiella particularly Pseudomonas aeruginosa. Effective against Aerobic bacteria (not obligate/facultative anaerobes) and tularemia.	Hearing loss Vertigo Kidney damage	Binding to the bacterial ribosomal subunit (some work by binding to the 50S subunit), inhibiting the translocation of the peptidyl-tRNA from the A-site to the P-site and also causing misreading of mRNA, leaving the bacterium unable to synthesize proteins vital to its growth.
Gentamicin	Garamycin
Kanamycin	Kantrex
Neomycin	Mycifradin
Netilmicin	Netromycin
Streptomycin
Tobramycin	Nebcin
Paromomycin	Humatin
Ansamycins
Geldanamycin		Experimental, as antitumor antibiotics
Herbimycin		Experimental, as antitumor antibiotics
Carbacephem
Loracarbef	Lorabid			prevents bacterial cell division by inhibiting cell wall synthesis.
Carbapenems
Ertapenem	Invanz	Bactericidal for both Gram-positive and Gram-negative organisms and therefore useful for empiric broad-spectrum antibacterial coverage. (Note MRSA resistance to this class.)	Gastrointestinal upset and diarrhea Nausea Seizures Headache Rash and allergic reactions	Inhibition of cell wall synthesis
Doripenem	Finibax
Imipenem/Cilastatin	Primaxin
Meropenem	Merrem
Cephalosporins (First generation)
Cefadroxil	Duricef		Gastrointestinal upset and diarrhea Nausea (if alcohol taken concurrently) Allergic reactions	Same mode of action as other beta-lactam antibiotics: disrupt the synthesis of the peptidoglycan layer of bacterial cell walls.
Cefazolin	Ancef
Cefalotin or Cefalothin	Keflin
Cefalexin	Keflex
Cephalosporins (Second generation)
Cefaclor	Ceclor		Gastrointestinal upset and diarrhea Nausea (if alcohol taken concurrently) Allergic reactions	Same mode of action as other beta-lactam antibiotics: disrupt the synthesis of the peptidoglycan layer of bacterial cell walls.
Cefamandole	Mandole
Cefoxitin	Mefoxin
Cefprozil	Cefzil
Cefuroxime	Ceftin, Zinnat
Cephalosporins (Third generation)
Cefixime	Suprax		Gastrointestinal upset and diarrhea Nausea (if alcohol taken concurrently) Allergic reactions	Same mode of action as other beta-lactam antibiotics: disrupt the synthesis of the peptidoglycan layer of bacterial cell walls.
Cefdinir	Omnicef, Cefdiel
Cefditoren	Spectracef
Cefoperazone	Cefobid
Cefotaxime	Claforan
Cefpodoxime	Vantin
Ceftazidime	Fortaz
Ceftibuten	Cedax
Ceftizoxime
Ceftriaxone	Rocephin
Cephalosporins (Fourth generation)
Cefepime	Maxipime		Gastrointestinal upset and diarrhea Nausea (if alcohol taken concurrently) Allergic reactions	Same mode of action as other beta-lactam antibiotics: disrupt the synthesis of the peptidoglycan layer of bacterial cell walls.
Cephalosporins (Fifth generation)
Ceftobiprole		Used to treat MRSA	Gastrointestinal upset and diarrhea Nausea (if alcohol taken concurrently) Allergic reactions	Same mode of action as other beta-lactam antibiotics: disrupt the synthesis of the peptidoglycan layer of bacterial cell walls.
Glycopeptides
Teicoplanin				inhibiting peptidoglycan synthesis
Vancomycin	Vancocin			inhibiting peptidoglycan synthesis
Macrolides
Azithromycin	Zithromax, Sumamed, Zitrocin	Streptococcal infections, syphilis, respiratory infections, mycoplasmal infections, Lyme disease	Nausea, vomiting, and diarrhea (especially at higher doses) Jaundice	inhibition of bacterial protein biosynthesis by binding irreversibly to the subunit 50S of the bacterial ribosome, thereby inhibiting translocation of peptidyl tRNA.
Clarithromycin	Biaxin
Dirithromycin	Dynabac
Erythromycin	Erythocin, Erythroped
Roxithromycin
Troleandomycin	TAO
Telithromycin	Ketek	Pneumonia	Visual Disturbance, Liver Toxicity.
Spectinomycin		Antimetabolite, Anticancer
Monobactams
Aztreonam	Azactam			Same mode of action as other beta-lactam antibiotics: disrupt the synthesis of the peptidoglycan layer of bacterial cell walls.
Penicillins
Amoxicillin	Novamox, Amoxil	Wide range of infections; penicillin used for streptococcal infections, syphilis, and Lyme disease	Gastrointestinal upset and diarrhea Allergy with serious anaphylactic reactions Brain and kidney damage (rare)	Same mode of action as other beta-lactam antibiotics: disrupt the synthesis of the peptidoglycan layer of bacterial cell walls.
Ampicillin	Principen
Azlocillin
Carbenicillin
Cloxacillin	Tegopen
Dicloxacillin	Dynapen
Flucloxacillin	Floxapen
Mezlocillin
Meticillin
Nafcillin
Oxacillin
Penicillin
Piperacillin
Ticarcillin
Polypeptides
Bacitracin		Eye, ear or bladder infections; usually applied directly to the eye or inhaled into the lungs; rarely given by injection	Kidney and nerve damage (when given by injection)	Inhibits isoprenyl pyrophosphate, a molecule which carries the building blocks of the peptidoglycan bacterial cell wall outside of the inner membrane
Colistin				Interact with the bacterial cytoplasmic membrane, changing its permeability.
Polymyxin B
Quinolones
Ciprofloxacin	Cipro, Ciproxin, Ciprobay	Urinary tract infections, bacterial prostatitis, community-acquired pneumonia, bacterial diarrhea, mycoplasmal infections, gonorrhea	Nausea (rare), irreversible damage to central nervous system (uncommon), tendinosis (rare)	inhibit the bacterial DNA gyrase or the topoisomerase IV enzyme, thereby inhibiting DNA replication and transcription.
Enoxacin	Penetrex
Gatifloxacin	Tequin
Levofloxacin	Levaquin
Lomefloxacin	Maxaquin
Moxifloxacin	Avelox
Norfloxacin	Noroxin
Ofloxacin	Floxin, Ocuflox

Trovafloxacin	Trovan	Withdrawn
Grepafloxacin	Raxar	Withdrawn
Sparfloxacin	Zagam	Withdrawn
Temafloxacin	Omniflox	Withdrawn
Sulfonamides
Mafenide		Urinary tract infections (except sulfacetamide and mafenide); mafenide is used topically for burns	Nausea, vomiting, and diarrhea Allergy (including skin rashes) Crystals in urine Kidney failure Decrease in white blood cell count Sensitivity to sunlight	Folate synthesis inhibition. They are competitive inhibitors of the enzyme dihydropteroate synthetase, DHPS. DHPS catalyses the conversion of PABA (para-aminobenzoate) to dihydropteroate, a key step in folate synthesis. Folate is necessary for the cell to synthesize nucleic acids (nucleic acids are essential building blocks of DNA and RNA), and in its absence cells will be unable to divide.
Sulfonamidochrysoidine (archaic)	Prontosil
Sulfacetamide
Sulfadiazine	Micro-Sulfon
Sulfamethizole
Sulfanilimide (archaic)
Sulfasalazine	Azulfidine
Sulfisoxazole
Trimethoprim	Trimpex
Trimethoprim-Sulfamethoxazole (Co-trimoxazole) (TMP-SMX)	Bactrim, Septra
Tetracyclines
Demeclocycline	Declomycin	Syphilis, chlamydial infections, Lyme disease, mycoplasmal infections, acne rickettsial infections, malaria. Note: Malaria is caused by a protist and not a bacterium.	Potentially Permanent Gastrointestinal upset Sensitivity to sunlight Potential toxicity to mother and fetus during pregnancy Enamel hypoplasia (staining of teeth) transient depression of bone growth	inhibiting the binding of aminoacyl-tRNA to the mRNA-ribosome complex. They do so mainly by binding to the 30S ribosomal subunit in the mRNA translation complex.
Doxycycline	Vibramycin
Minocycline	Minocin
Oxytetracycline	Terramycin
Tetracycline	Sumycin, Achromycin V, Steclin
Others
Arsphenamine	Salvarsan	Spirochaetal infections (obsolete)
Chloramphenicol	Chloromycetin	meningitis,	Rarely: aplastic anemia.	Inhibits bacterial protein synthesis by binding to the 50S subunit of the ribosome
Clindamycin	Cleocin	acne infections, prophylaxis before surgery
Lincomycin	Lincocin	acne infections, prophylaxis before surgery
Ethambutol	Myambutol	Antituberculosis
Fosfomycin	Monurol
Fusidic acid	Fucidin
Furazolidone
Isoniazid	I.N.H.	Antituberculosis
Linezolid	Zyvox	VRSA
Metronidazole	Flagyl	Giardia
Mupirocin	Bactroban
Nitrofurantoin	Macrodantin, Macrobid
Platensimycin
Pyrazinamide		Antituberculosis
Quinupristin/Dalfopristin	Syncercid
Rifampicin (Rifampin in US)		mostly Gram-positive and mycobacteria	Reddish-orange sweat, tears, and urine	Binds to the β subunit of RNA polymerase to inhibit transcription
Thiamphenicol		Gram-negative, Gram-positive, anaerobes. Widely used in veterinary medicine.	Lacks known anemic side-effects.	A chloramphenicol analog. May inhibit bacterial protein synthesis by binding to the 50S subunit of the ribosome
Tinidazole
Dapsone	Avlosulfon	Antileprotic
	Lamprene	Antileprotic
Generic Name	Brand Names	Common Uses	Possible Side Effects	Mechanism of action