**Core Concept**
The treatment of gonococcal and non-gonococcal urethritis involves the use of antibiotics that effectively target the causative pathogens, Neisseria gonorrhoeae and Chlamydia trachomatis, respectively. The choice of antibiotic must consider the rising rates of antibiotic resistance in these pathogens.

**Why the Correct Answer is Right**
Azithromycin is a macrolide antibiotic that is effective against both Neisseria gonorrhoeae and Chlamydia trachomatis. It works by inhibiting protein synthesis in bacteria through binding to the 50S ribosomal subunit. This results in the termination of protein synthesis, ultimately leading to the death of the bacterial cells. Azithromycin's broad-spectrum activity and convenience of dosing (single oral dose) make it an attractive option for the treatment of gonococcal and non-gonococcal urethritis.

**Why Each Wrong Option is Incorrect**
**Option A:** Clindamycin is a lincosamide antibiotic that is effective against a range of bacterial infections, but it is not the first-line treatment for gonococcal or non-gonococcal urethritis due to concerns about resistance and its less favorable pharmacokinetic profile compared to azithromycin.
**Option B:** Cefepime is a fourth-generation cephalosporin antibiotic with broad-spectrum activity, but it is not typically used to treat gonococcal or non-gonococcal urethritis, as other antibiotics like azithromycin are more convenient and effective.
**Option C:** Metronidazole is an antibiotic that is effective against anaerobic bacteria and protozoa, but it is not indicated for the treatment of gonococcal or non-gonococcal urethritis.

**Clinical Pearl / High-Yield Fact**
Azithromycin is a good choice for treating urethritis in patients with a history of penicillin allergy, as it is not a beta-lactam antibiotic. Additionally, its single-dose regimen can improve patient adherence and reduce the risk of treatment failure.

**✓ Correct Answer: D. Azithromycin**