Drugs Acting on Cell Membrane and Protein Synthesis Inhibitors: Downloadable Resources (PDF & PPT)
Download comprehensive notes on drugs acting on the cell membrane and protein synthesis inhibitors in PDF and PPT formats. These notes cover two major classes of antibiotics: those that disrupt bacterial cell membrane integrity and those that interfere with bacterial protein synthesis. Learn about their mechanisms of action, antibacterial spectrum, clinical uses, resistance mechanisms, and potential side effects. Ideal for students, researchers, and healthcare professionals. Download now for convenient offline access.
Keywords: Cell Membrane Antibiotics, Protein Synthesis Inhibitors, PDF, PPT, Download, Notes, Antibiotics, Polymyxins, Daptomycin, Aminoglycosides, Tetracyclines, Macrolides, Lincosamides, Chloramphenicol, Oxazolidinones, Streptogramins, Mechanism of Action, Antibacterial, Pharmacology, Ribosomes, 30S Subunit, 50S Subunit, Bacterial Resistance, Nephrotoxicity, Ototoxicity.
Drugs Acting on the Cell Membrane and Protein Synthesis Inhibitors: Mechanisms and Classes
This document provides an overview of two major classes of antibiotics: those that disrupt bacterial cell membrane integrity and those that inhibit bacterial protein synthesis. These antibiotics target essential bacterial processes, making them effective antibacterial agents.
I. Drugs Acting on the Bacterial Cell Membrane
These antibiotics disrupt the structure and function of the bacterial cell membrane, leading to leakage of cellular contents and cell death. They are generally more effective against Gram-negative bacteria, which have an outer membrane in addition to the cytoplasmic membrane.
- Polymyxins (e.g., Polymyxin B, Colistin):
- Mechanism of Action: Polymyxins are cationic, cyclic peptides that bind to the lipopolysaccharide (LPS) in the outer membrane of Gram-negative bacteria. This binding disrupts the membrane's integrity, leading to increased permeability, leakage of cellular contents, and cell death. Polymyxins are bactericidal.
- Spectrum: Primarily active against Gram-negative bacteria, including *Pseudomonas aeruginosa*, *Acinetobacter baumannii*, and *Klebsiella pneumoniae*. Often used as "last-resort" antibiotics for multidrug-resistant Gram-negative infections.
- Side Effects: Nephrotoxicity (kidney damage) and neurotoxicity (e.g., paresthesias, dizziness, muscle weakness) are major concerns.
- Daptomycin:
- Mechanism of Action: Daptomycin is a cyclic lipopeptide that binds to the bacterial cell membrane in a calcium-dependent manner. It inserts into the membrane, causing depolarization (loss of membrane potential) and potassium efflux, leading to cell death. Daptomycin is bactericidal.
- Spectrum: Active against Gram-positive bacteria, including methicillin-resistant *Staphylococcus aureus* (MRSA) and vancomycin-resistant enterococci (VRE). *Not effective against Gram-negative bacteria because it cannot penetrate the outer membrane.*
- Side Effects: Myopathy (muscle damage), elevated creatine phosphokinase (CPK) levels.
II. Protein Synthesis Inhibitors
These antibiotics inhibit bacterial protein synthesis by binding to bacterial ribosomes, which are different from eukaryotic ribosomes. This difference in ribosomal structure provides selectivity for bacterial cells. Protein synthesis inhibitors can be bacteriostatic (inhibit bacterial growth) or bactericidal (kill bacteria), depending on the drug and the concentration.
Bacterial ribosomes consist of two subunits: the 30S subunit and the 50S subunit. Protein synthesis inhibitors can target either of these subunits.
- Aminoglycosides:
- Examples: Gentamicin, Tobramycin, Amikacin, Streptomycin, Neomycin, Kanamycin.
- Mechanism of Action: Bind irreversibly to the 30S ribosomal subunit, causing misreading of mRNA and interfering with protein synthesis. They can also disrupt the bacterial cell membrane. Aminoglycosides are bactericidal.
- Spectrum: Primarily active against aerobic Gram-negative bacteria. Some have activity against certain Gram-positive bacteria. Streptomycin is used to treat tuberculosis.
- Side Effects: Nephrotoxicity (kidney damage), ototoxicity (hearing loss and balance problems), neuromuscular blockade (rare).
- Tetracyclines:
- Examples: Tetracycline, Doxycycline, Minocycline, Tigecycline.
- Mechanism of Action: Bind reversibly to the 30S ribosomal subunit, blocking the binding of aminoacyl-tRNA to the mRNA-ribosome complex, thus preventing the addition of amino acids to the growing peptide chain. Tetracyclines are bacteriostatic.
- Spectrum: Broad spectrum, including activity against Gram-positive and Gram-negative bacteria, as well as atypical bacteria (e.g., *Chlamydia*, *Mycoplasma*, *Rickettsia*).
- Side Effects: Gastrointestinal upset, phototoxicity, tooth discoloration (in children), bone deposition (in children), hepatotoxicity (rare).
- Macrolides:
- Examples: Erythromycin, Azithromycin, Clarithromycin.
- Mechanism of Action: Bind reversibly to the 50S ribosomal subunit, blocking the translocation step of protein synthesis (preventing the movement of the ribosome along the mRNA). Macrolides are usually bacteriostatic but can be bactericidal at high concentrations.
- Spectrum: Active against Gram-positive bacteria and some Gram-negative bacteria, as well as atypical bacteria (e.g., *Mycoplasma*, *Chlamydia*, *Legionella*).
- Side Effects: Gastrointestinal upset (especially erythromycin), QT prolongation, drug interactions (inhibition of CYP enzymes).
- Lincosamides:
- Examples: Clindamycin.
- Mechanism of Action: Binds to the 50S ribosomal subunit, similar to macrolides, inhibiting peptidyl transferase and preventing peptide bond formation. Clindamycin is usually bacteriostatic.
- Spectrum: Active against Gram-positive bacteria (including some MRSA) and anaerobic bacteria.
- Side Effects: Gastrointestinal upset, *Clostridioides difficile* infection (CDI) - a potentially serious superinfection.
- Chloramphenicol:
- Mechanism of Action: Binds reversibly to the 50S ribosomal subunit and inhibits peptidyl transferase activity, preventing peptide bond formation. Chloramphenicol is bacteriostatic.
- Spectrum: Broad spectrum, including activity against Gram-positive and Gram-negative bacteria, as well as some atypical bacteria.
- Side Effects: Bone marrow suppression (can be serious and irreversible), "gray baby syndrome" (in neonates). Due to its toxicity, chloramphenicol is generally reserved for serious infections when other antibiotics are not effective.
- Oxazolidinones:
- Examples: Linezolid, Tedizolid.
- Mechanism of Action: Bind to the 23S rRNA of the 50S ribosomal subunit, preventing the formation of the initiation complex (the first step in protein synthesis). Oxazolidinones are generally bacteriostatic.
- Spectrum: Active against Gram-positive bacteria, including MRSA and VRE.
- Side Effects: Myelosuppression (bone marrow suppression), peripheral neuropathy, optic neuropathy, serotonin syndrome (when combined with other serotonergic drugs).
- Streptogramins:
- Examples: Quinupristin/dalfopristin
- Mechanism of Action: Bind to the 50S ribosomal subunit.
- Spectrum: effective for gram-positive bacteria.
- Mupirocin:
- Binds to isoleucyl t-RNA synthetase
- Fusidic acid:
- Inhibits translocation by binding to EF-G
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