Antimicrobial drugs are the greatest contribution of the 20th century to therapeutics. Their advent changed the outlook of the physician about the power drugs can have on diseases. They are one of the few curative drugs. Drugs in this class differ from all others in that they are designed to inhibit/kill the infecting organism and to have no/minimal effect on the recipient. This type of therapy is generally called chemotherapy which has come to mean ‘treatment of systemic infections with specific drugs that selectively suppress the infecting microorganism without significantly affecting the host.’ The basis of selective microbial toxicity is the action of the drug on a component of the microbe (e.g. bacterial cell wall) or metabolic processes (e.g. folate synthesis) that is not found in the host, or high affinity for certain microbial biomolecules (e.g. trimethoprim for bacterial dihydrofolate reductase). Due to analogy between the malignant cell and the pathogenic microbes, treatment of neoplastic diseases with drugs is also called ‘chemotherapy’.
Anti-biotics: These are substances produced by microorganisms, which selectively suppress the growth of or kill other microorganisms at very low concentrations. This definition excludes other natural substances which also inhibit microorganisms but are produced by higher forms (e.g. antibodies) or even those produced by microbes but are needed in high concentrations (ethanol, lactic acid, H202). Initially the term ‘chemotherapeutic agent’ was restricted to synthetic compounds, but now since many antibiotics and their analogues have been synthesized, this criterion has become irrelevant; both synthetic and microbiologically produced drugs need to be included together. It would be more meaningful to use the term antimicrobial agent (AMA) to designate synthetic as well as naturally obtained drugs that attenuate microorganisms.
Antimicrobial drugs can be classified in many ways:
Narrow-spectrum: Penicillin G, streptomycin, erythromycin.
Broad-spectrum: Tetracyclines, Chloramphenicol
The initial distinction between narrow and broad-spectrum antibiotics is no longer clear cut. Drugs with all ranges of intermediate bandwidth, eg: extended spectrum penicillin, newer cephalosporins, aminoglycosides, fluoroquinolones are now available. However, the terms ‘narrow spectrum’ and ‘broad-spectrum’ are still applied.
1. Primarily bacteriostatic: Sulphonamides, Erythromycin, Tetracyclines, Ethambutol, Chloramphenicol, Clindamycin, Linezolid.
2. Primarily bactericidal: Penicillin, Cephalosporins, Aminoglycosides, Vancomycin, Polypeptides Nalidixic acid, Rifampin, Ciprofloxacin, Isoniazid, Metronidazole, Pyrazinamide, Cotrimoxazole.
Some primarily static drugs may become bactericidal at higher concentrations (as attained in the urinary tract), e.g. sulphonamides, erythromycin, nitrofurantoin. On the other hand, some bactericidal drugs, e.g cotrimoxazole, streptomycin may only be bacteriostatic under certain circumstances.
In the Absorption & Distribution process, a drug has to move across various biological membranes like cell wall, blood-brain barrier etc. the biological membrane is made up of 2 layers of phospholipids with intermingled protein molecules. All Lipid-Soluble substances get dissolved in cell membrane & they are easily permeated into the cells.
The success of antibacterial agents owes much to the fact that they can act selectively against bacterial cells rather than animal cells. This is largely because bacterial and animal cells differ both in their structure and in their biosynthetic pathways. Let us consider some of the differences between the bacterial cell (defined as prokaryotic ) […]
The main molecular targets for drugs are proteins (mainly enzymes, receptors, and transport proteins) and nucleic acids (DNA and RNA). These The main molecular targets for drugs are proteins (mainly enzymes, receptors, and transport proteins) and nucleic acids (DNA and RNA). These are large molecules ( macromolecules ) that have molecular weights measured in the […]
Why should chemicals, some of which have remarkably simple structures, have such an important effect on such a complicated and large structure as a human being? The answer lies in the way that the human body operates. If we could see inside our bodies to the molecular level, we would see a magnificent array of […]
The medicinal chemist attempts to design and synthesize a pharmaceutical agent that has a desired biological effect on the human body or some other living system. Such a compound could also be called a ‘drug’, but this is a word that many scientists dislike because society views the term with suspicion. With media headlines such […]