Antibacterials: Macrolides

Question 1

Erythromycin

Answer 1

• family: macrolide
• mechanism: Binds 50s subunit near peptidyltransferase center and prevents elongation step (transpeptidation) by blocking polypeptide exit tunnel
• kinetics: biliary excretion
• clinical: Atypicals, MAC in HIV patients, Legionella
• toxicity/interactions: drug metabolites inhibit cytochrome p450 enzymes, cholestatic hepatitis, anorexia, nausea, vomiting, and diarrhea

Question 2

Clindamycin

Answer 2

• family: macrolide
• mechanism: Binds 50s subunit near peptidyltransferase center and prevents elongation step (transpeptidation) by blocking polypeptide exit tunnel
• clinical: osteomyelitis, anaerobic infections (bacteroides), skin and soft tissue infections of staph and strep
• toxicity/interactions: Pseudomembranous colitis (C.difficil), diarrea, nausea, skin rashes, inhibit cytochrome p450 enzymes
• misc: not a macrolide but same mech

Question 3

Clarithromycin

Answer 3

• family: macrolide
• mechanism: Binds 50s subunit near peptidyltransferase center and prevents elongation step (transpeptidation) by blocking polypeptide exit tunnel
• clinical: Hemophilus influenza, chlamydia, legionella, moraxella, ureaplasma, and helicobacter pylori
• toxicity/interactions: Anorexia, nausea, vomiting, and diarrhea, inhibit cytochrome p450 enzymes; interacts with digoxin

Question 4

Azithromycin

Answer 4

• family: macrolide
• mechanism: Binds 50s subunit near peptidyltransferase center and prevents elongation step (transpeptidation) by blocking polypeptide exit tunnel
• kinetics: long half life in tissues
• clinical: Chlamydia trachomatis
• toxicity/interactions: Anorexia, nausea, vomiting, and diarrhea, inhibit cytochrome p450 enzymes

Question 5

Chloramphenicol

Answer 5

• family: macrolide
• mechanism: Binds 50s subunit near peptidyltransferase center and prevents elongation step (transpeptidation) by blocking polypeptide exit tunnel
• kinetics: Enters CNS
• clinical: Rarely used in US due to toxicity, sometimes considered serious rickettsial infections
• toxicity/interactions: Anemia (bone marrow suppresion), GI distress, Grey baby syndrome, inhibits cytochrome p450 enzymes (potentiates warfarin)
• misc: Bacteriostatic, not a macrolide but same mech