**Core Concept**
The patient's symptoms suggest a severe infection of the skull base, specifically the petrous apex, which is a rare but serious condition known as petrous apicitis. This condition is often associated with diabetes mellitus and can lead to severe complications if not treated promptly.

**Why the Correct Answer is Right**
The patient's symptoms, including excruciating pain in the ear, granulation in the meatus, and facial paralysis, are classic signs of petrous apicitis. Penicillin, specifically high-dose intravenous penicillin G, is the treatment of choice for this condition. This is because penicillin has excellent penetration into the petrous bone and can effectively target the causative organism, usually a beta-hemolytic streptococcus or Staphylococcus aureus.

**Why Each Wrong Option is Incorrect**

**Option B:** Ciprofloxacin is a fluoroquinolone antibiotic that has limited activity against the typical causative organisms of petrous apicitis. Furthermore, its poor penetration into the petrous bone makes it an inadequate choice for this condition.

**Option C:** 2nd generation cephalosporins, such as cefuroxime or cefaclor, have limited activity against Staphylococcus aureus and beta-hemolytic streptococci, making them unsuitable for the treatment of petrous apicitis.

**Option D:** Erythromycin is a macrolide antibiotic that is not effective against Staphylococcus aureus and has limited activity against beta-hemolytic streptococci. Its use in the treatment of petrous apicitis would be inappropriate.

**Clinical Pearl / High-Yield Fact**
In diabetic patients with petrous apicitis, prompt initiation of high-dose intravenous penicillin G is crucial to prevent severe complications, including meningitis and cranial nerve palsies. A high index of suspicion for this condition should be maintained in diabetic patients presenting with severe ear pain and facial paralysis.

✓ Correct Answer: A. Penicillin.