Antibiotics Mechanisms of Action Quiz

Study Notes

Key Concepts in Antimicrobial Therapy

Antibiotics: Substances that kill or inhibit the growth of microorganisms.
Selective Toxicity: Targeting microorganisms without harming human cells, exploiting differences in metabolism and structure.
Therapeutic Index: Ratio indicating the safety of a drug; the higher the index, the safer the drug.
Bacteriostatic vs. Bactericidal: Bactericidal drugs kill bacteria, whereas bacteriostatic drugs inhibit growth.

Mechanisms of Action

Antibiotics can:
- Inhibit cell wall synthesis (common in betalactams).
- Interfere with cell membrane function.
- Disrupt ribosomal function (protein synthesis), either reversibly (bacteriostatic) or irreversibly (bactericidal).
- Inhibit nucleic acid metabolism and block enzymatic activities (antimetabolites).

Microbial Classification

Important microorganisms include:
- Bacteria: e.g., Staphylococcus aureus.
- Viruses: e.g., HIV.
- Fungi: e.g., Candida albicans.
- Parasites: e.g., Plasmodium falciparum.

Types of Antimicrobial Therapy

Prophylaxis: Prevents infection in high-risk patients (e.g., immunosuppressed individuals).
Pre-emptive Therapy: For asymptomatic patients showing laboratory signs of infection; delivered prior to symptom development.
Empiric Therapy: Started before specific organisms are identified, based on common pathogens.
Definitive Therapy: Narrowed down once pathogen identification and susceptibility are available.
Suppressive Therapy: Continued at lower doses to manage chronic infections without complete eradication.

Pharmacokinetic Principles

Minimum Inhibitory Concentration (MIC): Lowest concentration of an antibiotic that prevents visible growth of bacteria.
Minimum Bactericidal Concentration (MBC): Concentration required to kill the bacteria.
Inoculum Effect: Increased bacterial density requires higher levels of antibiotics to achieve efficacy.

Bactericidal vs. Bacteriostatic Activities

Bactericidal Drugs: Useful in life-threatening infections; effective when host defenses are impaired.
Bacteriostatic Drugs: Require active host immune responses for efficacy and do not kill bacteria directly.
Post-Antibiotic Effect (PAE): Continued suppression of bacterial growth after removal of antibiotic.

Dosing Considerations

Continuous dosing maintains stable drug levels, while bolus dosing produces high peaks but may risk toxicity.
Time-Dependent Killing: Drug effects depend on maintaining concentrations above MIC for extended periods (e.g., beta-lactams).
Concentration-Dependent Killing: Increased effectiveness with higher peak concentrations (e.g., aminoglycosides).

Phases of Bacterial Growth

Lag Phase: Initial metabolic activity without cell division.
Log Phase: Rapid division; effective for beta-lactam drugs.
Stationary Phase: Cell division slows; balance of new cells and deaths.
Death Phase: Declining viable bacteria count.

Antimicrobial Drug Combinations

Most infections should ideally be treated with single agents; combination therapy may lead to synergism or antagonism.
Synergism: Combined effects are greater than individual effects; important in specific pathogen cases.
Antagonism: Combined effects are less effective; notable with bacteriostatic agents inhibiting the efficacy of bactericidal antibiotics.

Clinical Decision-Making

Selecting appropriate antibiotics involves understanding if a drug is cidal or static and using guidelines for effective treatment.

Description

Test your knowledge of how antibiotics work on bacterial cells with this quiz. Explore the different classes of antibiotics and their mechanisms of action, including inhibition of cell wall synthesis, interference with cell membrane function, and disruption of ribosomal function.