Mechanism Of Drug Action
Action of drugs are the biochemical and physiological mechanisms by which the chemical produces a response or change in a living organism. The goal is to inhibit or kill growth of microbes without harming the host's tissue. There are 5 main mechanisms a drug can effect microbe cell components.
1. Inhibition of Cell Wall Synthesis
2. Breakdown of Cell Membrane Structure or Function
3. Inhibition of Structures and Functions of DNA and RNA
4. Inhibition of Protein Synthesis
5. Block key Metabolic Pathways
1. Inhibition of Cell Wall Synthesis
2. Breakdown of Cell Membrane Structure or Function
3. Inhibition of Structures and Functions of DNA and RNA
4. Inhibition of Protein Synthesis
5. Block key Metabolic Pathways
Inhibition of Cell Wall Synthesis
Most bacteria contain a cell wall made of peptidoglycan which provides protection and support. The peptidoglycan layer is formed by two linear chains of alternating amino sugars; N-acetylglucosamine(NAG) and N-acetylmuramic acid(NAM). These sugars are connected by a peptide bond; a chemical bond formed between two molecules. Bacterial enzymes aids the bonds that link one or more polymer chain to another to form a cell wall.
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Some drugs such as penicillin and cephalosporin bind to specific proteins and cause inhibition of transpeptidase; an enzyme that links the peptidoglycan chain to form a cell wall. The result of the drugs weakens the cell wall and can no longer provide protection and is subject to lysis or rupture. This mechanism of drug action is the least harmful to humans since they do not have cell walls.
Antibiotics That Disrupt Cell Membrane
A cell that has a damaged cell membrane dies from lysis, disruption in metabolism, or inability to prevent foreign chemicals that are harmful. Polymyxin antibiotics damage the cell membrane function by dissolving the membrane phospholipids or interfere with the movement of molecules in or out of the cell also causing a leakage or proteins and nitrogen bases.
Drugs That Affect Nucleic Acid Synthesis
Antimicrobial drugs interfere with nucleic acid synthesis by blocking synthesis of nucleotides, inhibiting replication, or stopping transcription. Functioning DNA and RNA are required for proper translation and can effect protein metabolism. Several antibiotics inhibit DNA synthesis. They can bind and cross-link the double helix or inhibit DNA unwinding enzymes, thereby stopping DNA replication and repair.
Drugs That Block Protein Synthesis
Most drugs that inhibit protein synthesis react with ribosome-mRNA complex. Human cells have ribosomes, but the ribosomes of eukaryotes are different in size and structure from those of prokaryotes, so these antibiotics usually have a selection action against bacteria. Two possible targets of inhibition are the 30s subunit and 50s subunit ribosomes. Drugs that attach to the site on 30s subunit cause misreading of the mRNA leading to abnormal proteins. Drugs that attach to the site on 50s subunit prevents formation of peptide bonds.
Drugs That Block Metabolic Pathways
Certain antibiotics such as sulfonamides and trimethorim act by mimicking the normal substrate of any enzyme; competitive inhibition. The enzyme is no longer able to produce a needed product, thereby cellular metabolism slows or stops. Antibiotics like sulfonamides and trimethorim interfere with folate metabolism by blocking enzymes required for the synthesis of tetrahydrofolate; an enzyme needed by bacterial cells for the synthesis of folic acid production of DNA and RNA and amino acids. These antibiotics leave the human host unaffected because mammals derive folic acid from their diet.