Macrolides Overview Quiz

Macrolides

• Types: Erythromycin, clarithromycin, azithromycin, Roxithromycin, Olendamycin, Spiramycin
• Erythromycin Source: Natural
• Absorption: Absorbed orally but destroyed by stomach acid, given enteric-coated. IV administration is also possible.
• Blood-Brain Barrier (BBB) Penetration: Poor penetration
• Placental Barrier: Crosses the placental barrier, safe for use in pregnancy
• Metabolism: Metabolized in the liver
• Excretion: Excreted in urine and bile
• Mechanism of Action: Binds reversibly to 50S ribosomal subunits, inhibiting protein synthesis translocation. More active in alkaline environments.
• Bactericidal/Bacteriostatic Action: Bacteriostatic or bactericidal, depending on concentration
• Spectrum: Effective against Gram-positive cocci and bacilli, some Gram-negative cocci and bacilli (e.g., H. influenza)

Clarithromycin

• Compared to Erythromycin: More active against atypical bacteria, better oral absorption, less stomach upset
• Uses: Peptic ulcer treatment (eradicate H. pylori)
• Mechanism of Action (similar to erythromycin)

Azithromycin

• Compared to Erythromycin: More active against mycobacteria and Chlamydia, less active against Staphylococcus and Streptococcus
• Tissue Concentration: High tissue concentration; slow release from tissues
• Administration: Given once daily
• Mechanism of Action (similar to erythromycin)

Ketolides (Telithromycin)

• Type: Semi-synthetic macrolide
• Administration: Given orally once daily, high tissue concentration
• Spectrum: Active against Gram-positive, Gram-negative bacteria, and Chlamydia
• Mechanism of Action (similar to erythromycin)
• Uses: Useful in cases of bacterial resistance to macrolides

Lincosamides (Clindamycin & Lincomycin)

• Absorption: Absorbed orally and intravenously (IV). High concentration in bone and teeth.
• Metabolism: Metabolized by the liver, excreted in urine and bile
• Mechanism of Action: Similar to macrolides
• Spectrum: Similar to macrolides, but more active against anaerobes, except Clostridium difficile
• Indications: Treatment of anaerobic infections, prophylaxis against endocarditis, treatment of intra-abdominal/female genital infections
• Adverse Effects: Superinfection by Clostridium difficile (pseudomembranous colitis), gastrointestinal disturbances, liver dysfunction

Broad-Spectrum Antibiotics: Chloramphenicol

• Source: Natural
• Absorption: Well absorbed orally, inject or topical. Passes BBB.
• Metabolism: Metabolized by liver. Excreted primarily in urine.
• Mechanism of Action: Binds to 50S ribosomal subunit, inhibits peptidyl transferase leading to protein synthesis inhibition.
• Spectrum: Effective against Gram-positive, Gram-negative bacteria, rickettsia, and anaerobes.
• Indications: Respiratory tract infections, typhoid fever, meningitis, rickettsial infections, anaerobic infections and topical use (eye/ear).
• Adverse Effects: Bone marrow depression (e.g., agranulocytosis).

Tetracyclines

• Source: Natural and semi-synthetic
• Absorption: Variable, many are incompletely absorbed with food. Doxycycline unaffected by food.
• Chelation: Forms complexes with divalent cations (Ca2+, Mg2+, Al3+), reduces absorption.
• Distribution: Poor penetration of BBB, except minocycline. High bone, tooth, and calcified tissue concentration.
• Excretion: Primarily excreted via urine.
• Mechanism of Action: Binds 30S ribosomal subunit, inhibits protein synthesis
• Spectrum: Broad spectrum; gram positives and negatives, chlamydia, rickettsia, spirochetes, and amoeba (luminal)
• Indications: Variety of infections (respiratory, urinary, GI, other)
• Adverse Effects:
  • Toxic effects
  • Gastrointestinal disturbances
  • Superinfections
  • Caries
  • Photosensitivity
  • Teratogenicity
  • Other toxicities (hepatotoxicity,Fanconi syndrome,nephrotoxicity, CNS disturbances);