The development of antimicrobial therapy is considered to be one of most important advances in history of medicine. The efficacy and relative safety of these drugs has led to their wide spread use and over use. They are fundamentally different from each other types of drugs due to their ability to alter microbial flora and lead to antibiotic resistant micro organisms. The term antibiotic refers to substance produced by microorganisms to suppress growth of other microorganisms. The term antimicrobial agent refers to drugs synthesized in the laboratory and also natural antibiotics produced by microorganisms. Agents that inhibit synthesis of cell walls include Beta lactams such as Penicillin’s, Cephalosporin’s Monobactams and Carbapenems and others such as Vancomycin. Inhibitors of cytoplasmic membranes include Polymyxins. In fungi cell wall is damaged by polyene antibiotics or by Azoles. Inhibitors of nucleic acid synthesis include Quinolones which inhibit DNA gyrase and RNA polymerase inhibitor Rifampicin. Protein synthesis is inhibited by Aminoglycosides, Tetracyclines, Chloramphenicol, and Erythromycin. Finally folate antagonists such as Sulphonamides and Trimethoprim interfere with cell metabolism. A neoplasm is new growth of cells that may be benign or malignant. All malignant neoplasms are called cancers, a Latin word meaning crab, because cancer metastasizes or spreads outward from original site like legs of a crab. Uncontrolled cell division and metastasis are identifying characteristics of cancerous cells. As cancerous cells invade tissues and organs normal function is compromised and sometimes impaired to point of death unless treatment with surgery, radiation or chemotherapy drugs (anti neoplastic drugs) is begun. Chemotherapy drugs exert their action against rapidly dividing cancer cells. However some normal cells in the body also divide rapidly-cells lining GI tract, hair cells and blood cells. These normal cells are greatly affected by chemotherapy with resulting inflammation of mouth and GI tract, loss of hair, and decreased number of RBCs and WBCs. Hence in most cases drug therapy will produce only regression of disease and complications and relapse may eventually lead to death.