Overview
This lecture covers the macrolide class of antibiotics, focusing on their mechanism, key members (erythromycin and azithromycin), spectrum of activity, and dosing advantages.
Macrolide Antibiotics Overview
- Macrolides inhibit protein synthesis by targeting the 50S ribosomal subunit in bacteria.
- They were first discovered in 1952 from the Streptomyces genus; about half of all antibiotics come from this group.
- The earliest macrolide identified was erythromycin.
Mechanism of Action
- Macrolides block the formation of certain amino acid combinations during protein synthesis.
- This inhibition results in bacteriostatic action (stops bacterial growth, does not directly kill bacteria).
Comparison: Erythromycin vs. Azithromycin
- Erythromycin: mainly effective against gram-positive bacteria; limited by inability to enter gram-negative bacteria easily.
- Azithromycin (Z-Pak): more broad-spectrum, effective also against gram-negative bacteria.
- Erythromycin half-life: 1.5 hours; Azithromycin half-life: 68 hours.
Advantages of Azithromycin (Z-Pak)
- Long half-life allows for once-daily dosing and shorter overall treatment (e.g., three pills over three days).
- Shorter, simpler dosing improves patient compliance and treatment success.
Key Terms & Definitions
- Macrolides — A class of antibiotics that inhibit bacterial protein synthesis at the 50S ribosomal subunit.
- Bacteriostatic — Describes drugs that stop bacterial growth without killing the bacteria.
- Gram-positive bacteria — Bacteria with a thick peptidoglycan cell wall that retains Gram stain.
- Gram-negative bacteria — Bacteria with a thinner cell wall and outer membrane, do not retain Gram stain.
- Half-life — Time required for the concentration of a drug in the body to reduce by half.
- Streptomyces — A bacterial genus known as a major source of antibiotics.
Action Items / Next Steps
- Review mechanisms of action for other protein synthesis inhibitors.
- Memorize differences between erythromycin and azithromycin, especially spectrum and dosing.
- Prepare for potential exam questions on macrolide antibiotics.