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What are Antibiotics?

An antibiotic is a drug that kills or slows the growth of bacteria. These are chemicals produced by or derived from microorganisms. Antibiotics are the most commonly prescribed medications in modern medicine. There are two types of action produced by antibiotics one is bactericidal action i.e. they work by killing bacteria and other is bacteriostatic action which stops the multiplication of bacteria.

An ideal antibiotic has following parameters such as:

• Specific action
• Doesn’t kill normal flora
• High therapeutic index
• Least side effects such as allergy and toxicity
• Emergence of resistance should be slow

What is the role of Antibiotics?

They are used to kill or stop the activity of bacteria. Bacteria are one of the smallest and most abundantly present on the earth. They have a quality of getting adaptive to new conditions in order to survive. Not all bacteria cause disease some of them live on our skin surfaces and inside our bodies without causing us harm. They also help in the digestion of food in gut. Bacteria can be classified on the basis of their shapes:

• Bacilli are rod shaped and generally cause typhoid fever.
• Cocci are spherical shape and causes Gonorrhea.
• Spirochaetes are spiral shape and causes Syphilis 
• Vibrio is comma shaped and causes Cholera.

There are an infinite number of bacterial diseases that can cause mild to life threatening infections such as:

• Skin infections such as folliculitis , eczema and school sores
• Otitis Media
• Sexually transmitted disease
• Urinary tract infections
• Bacterial pneumonia
• Bacterial gastroenteritis
• Bacterial meningitis
• Septicemia

Classification of Antibiotics

They are classified on the basis of the mode of action they produce in order to cure bacterial infections.

Cell wall synthesis inhibitors

They are bactericidal drugs. They inhibit the formation of bacterial cell wall by interference with the synthesis of peptidoglycan. They are also known as beta lactam antibiotics. They act against various bacteria by stopping their multiplication and will not be effective against bacteria which lacks peptidoglycan cell wall. They are prescribed in bacterial sinusitis, mesotitis, lower respiratory tract infections, urinary and hepatobiliary tract infections, purulent gynecological infections and other community-acquired infections.

Antibiotic and it's types

• Beta lactam Penicillin: Natural - Penicillin G, Anti staphylococcal Methicillin, Drugs with extended spectrum are Aminopenicillins, Carboxypenicillins

Combination drugs such as Amoxicillin + Clavulanic Acid ;Ampicillin + Sulbactam; Ticarcillin + Clavulanic Acid Piperacillin + Tazobactam 

Aminopencillin - Mecillinam

• Beta lactam Cephems: 

First generation cephalosporins – Cefalotin, Cefalexin
Second generation – Cefuroxim, cefoxitin
Third generation- Cefotaxim , Ceftriaxon
Fourth generation- Cefpirom, Cefepim

• Carbapenems : Broad spectrum antibiotics such as Imipenem, Meropenem

• Monobactams: Aztreonam

 Protein synthesis inhibitors 

They act by inhibiting the RNA formation of bacteria. Protein is formed in the cells containing a code in the DNA, and then it is transcribed into RNA by an enzyme called RNA polymerase. By the actions of ribosome, it is translated into proteins. Each ribosome contains two sub units one is (30 S) and other is 50 (S). The drugs falling in this category acts by inhibiting these subunits and stops the formation of proteins which are needed by the bacteria for their survival.

• Amino glycoside antibiotics are used to treat gram negative infections. Drugs such as Amikacin, Gentamicin, Kanamycin and Streptomycin are prescribed for conditions like infections produced by Chlamydia, Rickettsia and capsulated pathogens like Salmonella typhi
• Tetracycline act by stopping the protein synthesis and is given in the treatment of various infections caused by non-pyogenic bacteria
• Chloramphenicol acts the same way as that of tetracycline but the target site is different. It binds to 50 (S) subunit and inhibits the elongation of proteins
• Other drugs are Linezolid, Rifampin which shows bactericidal or bacteriostatic activity depending upon the concentration. 
• Macrolide works by ceasing the formation of protein at ribosomal level. These are bacteriostatic drugs and are active against respiratory tract infections such as atypical pneumonia, tonsillitis and in urogenital infections. Erythromycin, Roxithromycin and Spiramycin, all are the drugs that fall in this category

Folate synthesis inhibitor

Folic acid is a key ingredient for the formation of DNA and chromosomes. It is a good selective target as humans doesn’t synthesize folic acid. Sulfonamides drugs like Sulfamethoxazole, Sulfacetamide and Trimethoprim bind with the enzymes that are needed for the formation of folic acid. They are recommended in conditions like urinary tract infections, chronic bronchitis, Otitis media and enteritis.

DNA synthesis inhibitors

Drugs are bactericidal in action as it rapidly diffuses through the peptidoglycan cell membrane and inhibits the enzyme DNA-gyrase and hinders the DNA super coiling process which in turn leads to death of bacteria.

Drugs such as Ciprofloxacin, Norfloxacin and Levofloxacin stop the synthesis of nucleic acid. These drugs are cost effective and are given in intestinal infections, bone and joint infections, biliary tract infections and in many sexually transmitted diseases.

Mycolic acid inhibitors

Mycolic acid is a key ingredient of mycobacterium cell wall. Isonazid is a drug which inhibits the formation of cell wall of bacteria that causes tuberculosis. It is a first line medication in the prevention and treatment of tuberculosis.

RNA synthesis inhibitors

Rifampin is a drug that inhibits DNA-dependent RNA polymerase activity in susceptible cells and thus doesn’t allow the formation of bacterial RNA and causes cell death. It is bactericidal and have broad spectrum of activity against all pathogens. It is the most preferred drug given in tuberculosis and related infections and is also given in the treatment of Hansen’s disease.

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