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There are chemical substances around us at every moment.
We ourselves are a beautiful chemical creation and all our activities are controlled by chemicals. Our life depends upon many chemical substances like medicines, drugs used as disinfectants, antibiotic and antiseptics.

Drugs are the chemical substances which have capability of curing certain diseases but they become habit and show serious side effect. On the other hand, medicines are the chemical substances used in several diseases, impart minimum side effects.

There are various ways to classify drugs.

  1. On the basis of their pharmacological effect
  2. On the basis of action on a particular biochemical process
  3. On the basis of chemical structure
  4. On the basis of molecular target


What are Antibiotics?

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Antibiotic is a combination of two Greek word which means “against life”. These are chemical substances which produced by some microorganisms and have capability to deactivate or kill other microorganisms, generally infection causing bacteria.

They are very reactive even in a very low concentration of them. The first antibiotic was penicillin which was discovered in 1929 by Alexander fleming from a mold culture. Now penicillin is a widely used antibiotic produced by microbial strain chrysogenum and its mutant.

Penicillin is a group of closely related compounds and consists of one acyl side chain, beta-lactam ring and one thiazolidine ring. The main disadvantage of antibiotics is that they can fight only with bacterial infections and do not work against viral infections, like flu, common cold, sore throat, mumps, bronchitis, etc.
Some of the antibiotics have serious side effects also; this is because some time antibiotic is not affected on virus and the chances of emergence of antibiotic resistant bacteria increases. Hence when an actual bacterial infection happens, the antibiotic is not able to kill them due to developed resistance.

On the basis of their specificity towards microorganisms, antibiotics can be classified either as bactericides or as bacteriostatic. Bactericides antibiotics used for killing bacteria only while bacteriostatic antibiotics are not killing them but slow down their rate of growth. Some common examples of both types of antibiotics are as follows.

Bactericides antibiotics
Bacteriostatic antibiotics
Daptomycin Tetracydines
Penicillin derivatives (penams)
Cephalosporins (cephems)

Another to classify antibiotics is on the basis of their action on bacteria, which is broad spectrum or narrow spectrum. A broad spectrum antibiotic can be effective against several different types if harmful bacteria like Chloramphenicol which can be given orally in case of typhoid, dysentery, acute fever, meningitis, pneumonia and certain forms of urinary infection.

However penicillin is a narrow spectrum antibiotic as it is effective only in case of those diseases which caused by various cocci and some gram positive bacteria.

On the basis of the chemical structure of antibiotics they can be classified as follows:

1. Penicillins

The antibiotics of this class are also called as beta-lactam antibiotics. They used to destroy the cell walls of the bacteria during their reproduction process. Some common examples of this class are penicillin G, penicillin V, ampicillin, ticarcillin, cloxacillin, oxacillin, amoxicillin and nafcillin.

2. Cephalosporins

They are bactericidal agents like cefadroxil, cefazolin, cephalexin, cephapirin, and cephalothin and used for those cases which are sensitive for penicillin antibiotics.

3. Aminoglycosides

These antibiotics inhibit the protein formation of bacteria-invading cells. Fo example; gentamicin, streptomycin and neomycin.

4. Macrolides

These antibiotics also interfere with the protein formation of invading bacteria and prevent bacterial protein biosynthesis. Like; azithromycin, clarithromycin and erythromycin.

5. Sulfonamides

Their action on microorganism is very similar to penicillin for fighting the bacterial infection. The most
common example of sulphonamide is gantrisin.

6. Fluoroquinolones

This class of antibiotics is latest development in chemotherapy. Some examples of these types of
antibiotic are enoxacin, levofloxacin and ofloxacin. They are relatively safe antibiotics as easily absorbed by body and can be given orally.

7. Tetracyclines

They are wide spectrum antibiotics used for infections of the middle ear, respiratory tract, urinary tract etc, but with various side effects. For example; tetracycline, deoxycycline and minocycline.

8. Polypeptides

They are quite toxic and used for skin surface only. For example; bacitracin, polymyxin B and colistin.

Natural Antibiotics

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There are many natural antibiotics which we can see in our daily life and have very less or no side effect. Apart from that they are quite effective and show long term effects. Some of the common examples of natural antibiotics are as follow.
  1. Olive Leaf Extract: Olive leaf extract is a good natural antibiotics which can also effective on various microbes including viruses. This extract also shows free radical scavenging abilities which linked with aging and disease.
  2. Garlic: It is a naturally occurring antibiotic, has anti-fungal property, and also an antiviral agent. However it contains two minerals; potassium and germanium which are critical to good health and also contains Allicin which is sulfur compound. These mineral and sulfur compound are act as phytochemicals which have ability to boost the immunity.
  3. Green tea: It has capability to work against certain strains of oral bacteria due to the presence of epigallocatechin gallate (EGCG) which is an active ingredients of green tea.
  4. Oregano Oil: This is one of most effective natural antibiotics which has ability to killed 96% of all pneumococcus bacteria, 92% of all neisseria, proteus, and staphylococcus bacteria. Oregano oil can eliminated 83% of streptococcus and 78% of enterococcus, which are linked with rheumatic fever , anorexia, scarlet fever, toxic shock syndrome, wound infections, cystitis and strep throat.
  5. Echinacea: It is a well known herbal remedies which is widely used for flus, colds, and other bacterial infections. It is also effective as a blood purifier as it can stimulate the immune system and increases white blood cell counts. The only limitation with this antibiotic is that it can be effective only when taken over longer periods of time.
  6. Goldenseal: Like Echinacea herb, Goldenseal is also an herb which has antibacterial and anti-fungal properties. It is often used for the treatment of sinus and ear infections, sore throats and vaginal infections. There are some limitations with this herb is that it cannot be taken during pregnancy and by hypoglycemics as it lowers the blood sugar levels.
  7. Myrrh: This is another herb which has antiseptic, antibiotic and antiviral properties.
  8. Colloidal Silver: This is an oldest and most controversial natural antibiotic which was very common during the 19th century for bacterial infections. It is quite effective for a variety of topical uses like ring worm and other fungal infections. It has ability to inhibit the growth of bacteria as well as viruses.
  9. Natural Antibiotics in Mammals: During sickness human body can create their own natural antibiotics which are basically natural peptides also known as cathelicidins. They distributed in tissue and white blood cells as they have ability to inhibit microbial growth and fight infections.

Artificial Antibiotics

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On the basis of their origin, antibiotics can be classified as
  1. Natural antibiotic: They derived from fungal sources and develop resistance faster to the natural antimicrobials as they already exposed to these compounds in nature. They are more toxic than other type of antibiotics. For example, Benzylpenicillin.
  2. Semi-synthetic antibiotic: They used to decreased toxicity and increased effectiveness like Ampicillin , Amikacin.
  3. Artificial or Synthetic antibiotic: These drugs prepared in laboratory by chemical reactions. They have high effectiveness and less toxicity compare to other antibiotics. They can be broad or narrow spectrum and produced by certain organisms. For example, Nitrofurans and Quinolones, Moxifloxacin, Norfloxacin. The toxicity of antibiotic is inversely related to effectiveness. Synthetic or artificial antibiotics have high effectiveness but less toxicity compare to natural antibiotics.
Artificial Antibiotics

List of Antibiotics

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Some common antibiotics with their class and brands are as follow;

Mechanism of Action of Antibiotics

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Different antibiotics react selectively with different microbes or molecules on certain organelles like cell wall, nucleic acid or cell membrane and the presence of antibiotic interrupt their synthesis. Some antibiotics interfere with the synthesis of peptidoglycan which is a most important component of the cell wall.

Mechanism of Action of Antibiotics

Hence mechanism of antibiotics involves inhibition on a certain levels. All these antibiotics show various mode of action. Some of the modes of action are as follows.
  • Cell Wall Synthesis Inhibitors: Some antibiotics like beta-lactams, cephalosporins and glycopeptides inhibits the ability of microorganism to synthesize the cell the wall which mainly contains murein and peptidoglycan.
  • Protein Synthesis Inhibitors: Some antibiotics like Streptomycine, Erythromycine, tetracyclines, chloramphenicol, lincomycin, kanamycin disulphate salts, aminoglycosides and macrolides interfere in the formation of protein synthesis of microbes.
Protein Synthesis Inhibitors

  • Cell Membrane Inhibitors: Antibiotics like polymyxins interrupt the integrity and structure of cell membranes, hence killing them. These types of antibiotics are generally effective on gram –ve bacteria as they have a definite cell membrane.

Cell Membrane Inhibitors

  • Effect on Nucleic Acids: The whole existence and life of any living system depends on DNA and RNA present in every living cell. Some antibiotics like etopocide, rifampcin, quinolones and rifamycins bonded with those proteins which are essential for the processing of these nucleic acids. Hence these antibiotics block the synthesis of nucleic acid and therefore affect the growth of the living cells.
  • Competitive Inhibitors: Some antibiotics competitively inhibit the important metabolic pathways happen inside the bacterial cell. These antibiotics resemble a microbial substrate and compete with that substrate for the limited microbial enzyme. The antibiotic ties up the enzyme and blocks a step in metabolism. They are also called as anti-metabolites or growth factor analogs. For example; Sulfonamides like Gantrisin and Trimethoprim.

Competitive Inhibitors

Some antibiotics with their mechanism are as follows.

Antibiotics Mechanism of Action

Uses of Antibiotics

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  • Usually an antibiotic is a chemical substance which used in medicine to treat diseases that are caused by bacteria. Some antibiotics are also effective on fungi and protozoa.
  • The group of unicellular microorganisms which are invisible with the naked eye are called as bacteria. Some bacteria are either harmless or pathogenic in human body.
  • Pathogenic bacteria are two types. Gram-positive (have no outer membrane) and Gram-negative bacteria (have outer membrane). In human body most pathogenic bacteria are Gram-negative. Both type of pathogenic bacteria are harmful for human health and has to be treated.
  • Antibiotics are the best drugs for the treatment of bacterial infections which eliminate the bacteria completely (bacteriocidal) or inhibit their growth (bacteristatic) by protein inhibition or cell wall inhibition.
  • The selection of antibiotic depends upon the type of microbes as well as range of antibiotics. Some antibiotics can kill or inhibit the growth of certain bacteria only, called as the narrow-spectrum antibiotics like penicillin.
  • While those antibiotics which target wider range of bacteria is called as broad-spectrum antibiotics like chloramphenicol. Some common antibiotics with their class and uses are as follow.
Class of antibiotic Antibiotic Uses
  • Erythromycin
  • Clarithromycin
  • Azithromycin
  • Oxithromycin
Treatment of infection in respiratory tract and genital, gastrointestinal tract
  • Amikacin
  • Gentamicin
  • Kanamycin
  • Neomycin
  • Streptomycin
  • Tobramycin
Treat the infections caused by gram-negative bacteria.
Cephalosporin1. First generation
  • Cephazolin
  • Cefadroxil
  • Cephalexin
  • Cephradine
2. Second generation
  • Cefaclor
  • Cefuroxime
  • Cefprozil
  • Loracarbef
3. Third generation
  • Cefotaxime
  • Cefixime
  • Cefpodoxime
  • Ceftazidime
  • Cefdinir
4. Fourth generation
  • Cefepime
  • Cefpirome
Used the treatment of pneumonia, tonsillitis, bronchitis, strep throat, staph infections and various types of skin infections
  • Ciprofloxacin
  • Gatifloxacin
  • Gemifloxacin
  • Levofloxacin
  • Moxifloxacin
  • Norfloxacin
  • Ofloxacin
  • Trovafloxacin
Used in the treatment of infection of Urinary tract, skin, respiratory system
  • Amoxicillin
  • Ampicillin
  • Bacampicillin
  • Oxacillin
  • Penicillin
Used in the treatment of infection of skin, teeth, ear, respiratory tract and urinary tract.
  • Tetracycline
  • Doxycycline
  • Minocycline
Used in the treatment of mild acne, Rocky Mountain spotted fever, Lyme Disease, upper respiratory tract infection, urinary tract infections, Sexually transmitted diseases, typhus.

Side Effects of Antibiotics

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Antibiotics may have side effects. Compare to other drugs, antibiotics are screened for any negative effects before approval for clinical use, and are considered safe. However the reaction and effect of antibiotic depends on the dose prescribe by doctor as well as the tolerance power of patient and the microbe which targeted.

The side effect of antibiotic can be ranged from mild to very serious. Some of the more common side effects may include,
  • Soft stools
  • Diarrhea
  • Mild stomach upset
  • Vomiting
  • Severe abdominal cramps
  • Allergic reaction like shortness of breath, hives, swelling on face and tongue, fainting
  • Rashes on skin
  • Vaginal itching and discharge
  • White patches on the tongue
  • Some allergic reactions like photo dermatitis and anaphylaxis

Some antibiotic with their side effects are as follows.

Antibiotic Side Effect
Penicillins Diarrhea, Nausea, vomiting, and upset stomach, skin rashes, fever, and anaphylactic shock
Cephalosporins Diarrhoea, nausea, mild stomach cramps
Fluoroquinoloness Nausea, vomiting, diarrhea, abdominal pain, Effects on central nervous system like headache, confusion and dizziness, phototoxicity (more common with lomefloxacin and sparfloxacin)
Tetracyclines Diarrhea , Cramps or burning of the stomach
Macrolides Nausea, vomiting, and diarrhea, temporary auditory impairment, allergic reactions like angioedema, anaphylaxis, and dermatologic reactions, irritation in stomach
Aminoglycosides Ototoxicity (damage to the ear and hearing), nephrotoxicity (kidney damage)
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