Question

Antibiotic	Target	MOA (Mechanism of Action)
Penicillin
Oxacillin
Ampicillin
Bacitracin
Vancomycin
Isoniazid
Ethambutol
Chloramphenicol
Tetracyclines
Aminoglycosides (streptomycin, Neomycin, & Gentamycin
Erythromycin
Polymyxins
Polyenes (Amphoterecin B)
Sulfanilamide
Rifamycin
Acyclovir
Nalidixic Acid
Neviropine
Zanamivir
Amantadine

Answer 1

INTRODUCTION

Antibiotics are generally defined as substances derived from a microorganism or produced synthetically, that destroys or limits the growth of a living organism.

ANTIBIOTICS – Classification

I. According to antimicrobial activity

1. Bactericidal

2. Bacteriostatic

II. According to bacterial spectrum of activity

1. Narrow spectrum

2. Broad spectrum

III. According to how the drugs are absorbed in the site of administration to attain significant concentration for the treatment of corresponding infection successfully ;

1. Locally acting

2. Systemic

IV. According to mechanism of action;

1. Inhibit bacterial cell wall synthesis .

2. Alters the function and permeability of the cell membranes of the pathogens.

3. Inhibit protein synthesis (translation and transcription).

4. Inhibit nucleic acid synthesis.

MECHANISM OF ACTION WITH EXPLANATIONS

ANTIBIOTIC TARGET MOA( MECHANISM OF ACTION) Penicillin Inhibition of cell wall synthesis –i.e.. block peptidoglycan (murein) synthesis of the bacteria.As a result of defective cell wall synthesis – cell lysis happens and leads to death of the bacterias. Ampicillin Their mode of action is by inhibiting bacterial cell wall synthesis - by binding to the PBPs(penicillin-binding proteins) - thereby inhibiting the final transpeptidation step of peptidoglycan synthesis in bacterial cell walls. Oxacillin Bactericidal nature - inhibits bacterial cell wall synthesis by binding with one or more of the penicillin binding proteins (PBPs).(similar action compared to Ampicillin). Bacitracin Inhibition of cell wall synthesis/cell wall inhibitors. Vancomycin Inhibit precursor for bacterial cell wall synthesis. Isoniazid They form complex with Acyl carrier protein & Beta ketoacyl carrier protein synthase and Inhibits mycolic acid synthesis – an important component of cell wall. Ethambutol Mode of action is by Inhibiting specifically the enzyme mycobacterial arabinosyl transferases.These particular enzymes are involved in the polymerization reaction of arabinoglycans - important structural component of the mycobacterial cell wall.Thus produces defective cell walls. Chloramphenicol Inhibition of protein synthesis (are group of drugs that acts on the 50S subunits and affects the protein synthesizing machinery of the corresponding pathogen) Tetracyclines Inhibits the bacterial protein synthesis by binding specifically to 30S subunit of ribosome – thus blocking the attachment of the t-RNA-amino acid to the m-RNA- ribosome complex. Aminoglycosides(streptomycin, Neomycin, & Gentamycin) Inhibition of protein synthesis(Drugs that act on the 30 S subunit) Erythromycin Inhibition of protein synthesis (Drugs that act on the 50 S subunit) –binding site is 23S rRNA. Polymyxins Inhibition of cell membrane function. Polyenes (Amphoterecin B) Anti –fungal activity – changes permeability of the fungal cell membrane.( disseminates mycoses ). Sulfanilamide They are the chemical analogues of p-aminobenzoic acid (PABA) ,thus competitively inhibits the bacterial enzyme, that are responsible for the synthesis of folic acid.Thus atlast results in the inhibited synthesis of bacterial folic acid, which is the most important factor of microbial life. Rifamycin Inhibition of nucleic acid synthesis( specifically -inhibition of RNA synthesis) by binding to DNA dependent RNA polymerase and thereby blocking the initiation of bacterial RNA synthesis. Acyclovir Results in the inhibition of DNA synthesis as well as viral replication by competing with the substrate deoxyguanosine triphosphate for the enzyme viral DNA polymerase and being incorporated into viral DNA. Nalidixic Acid They block the bacterial DNA synthesis by inhibiting the enzymes that are very important in DNA replication -bacterial topoisomerase (DNA gyrase II) & topoisomerase. Thus the action of gyrase gets inhibited ,blocking DNA replication or transcription ,ultimately resulting in the death of bacteria. Neviropine They act by stopping Human influenza virus (HIV)production by binding directly onto the reverse transcriptase enzyme (non-competitively) and preventing the conversion of RNA to DNA. Zanamivir Inhibition of enzyme- influenza neuraminidase results in inhibition of virus particle release from host cells by binding to the active site of the neuraminidase enzyme. Thus blocking the release of progeny virions from infected host cells, which stops the spread of infection. As the viral replication rate thus reduced, the immune system can more effectively destroy any remaining viruses Amantadine It acts at uncoating as well as in the viral assembly during viral replication by blocking the viral membrane matrix protein, M2, which functions as a channel for hydrogen ion. This channel is important for the fusion of the viral membrane with the cell membrane that ultimately forms the endosome (during internalization of the virus by endocytosis).So replication of the virus gets failed.