This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Skin, Subject name: Pharmacology
Which is not used in acne:(2003) 
Select and explain. 
A. Erythromycin, B. Ampicillin, C. Clindamycin, D. Doxycycline
B: Ampicillin
Answer: B: Ampicillin 
Explanation: bRef: KDT, 5th ed, p. 800, 801 & 4th ed, p. 858s