This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Skin
A 17 year old girl with Acne has been taking a drug for the last two years. Show now presents with blue black pigmentation of nails. The likely medication causing the above pigmentation is 
Select and explain. 
A. Tetracycline, B. Minocycline, C. Doxycycline, D. Azithromycin
B: Minocycline
Answer: B: Minocycline 
Explanation: B i.e. MinocyclineAmongst tetracyclines (tetracycline/ minocycline/ doxycycline) pigmentation is most commonly associated with minocyclineQ. A diffuse blue-black/blue- gray/ muddy hyper pigmentationQ is an uncommon but troublesome side effect of prolonged minocycline therapy. Sites of involvement include sun exposed skin, mucus membranes (eg conjunctiva), nails, teeth, sclera, thyroid & bonesQ.Two side effects unique to minocycline are drug induced lupus & blue black pigmentation. Tetracycline induced nail discolouration is yellow.