Review Question - QID 106430

The woman in this clinical vignette is experiencing urinary frequency, discomfort, and vaginal discharge from a Chlamydial infection, which is treated with doxycycline. Doxycycline works by binding to the 30S ribosomal sub-unit and preventing aminoacyl-tRNA attachment.

Tetracyclines are a group of bacteriostatic antibiotics that function by binding to the 30S ribosomal subunit. They inhibit protein synthesis by preventing attachment of aminoacyl-tRNAs to the ribosomal A site. Bacteria are more susceptible to tetracyclines than humans because they actively pump tetracycline into their cells. Caution must be taken when using tetracylines, as they can cause phototoxic dermatitis when exposed to sunlight. Other side effects include nephrotoxicity, hepatotoxicity, discoloration of teeth, and inhibition of bone growth in children and developing fetuses.

Figure A demonstrates doxycycline photoxicity after sun exposure.

Incorrect answers:
Answer 1: Chloramphenicol blocks the peptidyltransferase on the 50S ribosomal subunit.
Answer 2: Metronidazole forms toxic free radicals that damage DNA.
Answer 4: Azeotram binds to PBP3 preventing the cross-linking of the peptidoglycan layer.
Answer 5: Azithromycin blocks peptide translocation by binding to the 23S rRNA of the 50S ribosomal subunit.