Controlling Microbial Growth in the Body: Antimicrobial Drugs (Chapter 10 Study Notes)

Controlling Microbial Growth in the Body: Antimicrobial Drugs

Key Terms

This section introduces important terminology related to antimicrobial drugs and their spectrum of activity.

• Broad Spectrum: Antimicrobial drugs that are effective against a wide variety of microbial species, including both Gram-positive and Gram-negative bacteria. These are useful when the causative agent of an infection is unknown, but may disrupt normal microbiota.

• Narrow Spectrum: Antimicrobial drugs that are effective against a limited range of microorganisms, often targeting specific families or groups. These are preferred when the pathogen is known, as they minimize disruption to normal flora.

Methods of Antimicrobial Action

Antimicrobial drugs control microbial growth by targeting specific structures or functions essential to microbial survival.

• Inhibiting Protein Synthesis: Many antibiotics (e.g., tetracyclines, macrolides) bind to bacterial ribosomes, preventing translation and thus protein production.

• Preventing Attachment: Some antivirals block the attachment of viruses to host cell receptors, preventing infection (e.g., entry inhibitors in HIV therapy).

• Inhibition of DNA or RNA Synthesis: Drugs such as quinolones and rifamycins interfere with nucleic acid synthesis, inhibiting replication and transcription.

• Inhibiting Metabolic Pathways: Some drugs (e.g., sulfonamides) act as competitive inhibitors of enzymes in key metabolic pathways, such as folic acid synthesis in bacteria.

• Disrupting Cell Wall Synthesis: Beta-lactam antibiotics (e.g., penicillins, cephalosporins) inhibit the synthesis of peptidoglycan, weakening the cell wall and causing lysis.

• Breakdown of Cytoplasmic Membrane: Polymyxins and some antifungals disrupt membrane integrity, leading to leakage of cellular contents and cell death.

Example: Penicillin inhibits cell wall synthesis, making it effective against actively growing Gram-positive bacteria.

Methods of Administration

The route of administration affects the efficacy and distribution of antimicrobial drugs in the body.

• Oral Administration: Drugs are taken by mouth and absorbed through the digestive tract. Convenient but may be less effective if the drug is poorly absorbed or destroyed by stomach acid.

• Intramuscular (IM): Drugs are injected into muscle tissue, allowing for slower, sustained release into the bloodstream.

• Intravenous (IV): Drugs are administered directly into the bloodstream, providing rapid and complete distribution throughout the body.

Additional info: The choice of administration depends on the drug's properties, the severity of infection, and patient factors.

Side Effects of Antimicrobial Drugs

While antimicrobial drugs are essential for treating infections, they can also cause adverse effects.

• Toxicity: Some drugs can damage host tissues or organs (e.g., nephrotoxicity from aminoglycosides).

• Allergies: Hypersensitivity reactions can occur, ranging from mild rashes to life-threatening anaphylaxis (e.g., penicillin allergy).

• Increase in Resistance: Overuse or misuse of antimicrobials can select for resistant strains, reducing drug effectiveness and complicating future treatment.

Example: The emergence of methicillin-resistant Staphylococcus aureus (MRSA) is a major public health concern due to increased resistance.