This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitamin, Subject name: Pharmacology
Which of the following is a topical vit. D analogue- 
Select and explain. 
A. Cholecalciferol, B. Doxercalciferol, C. Calcipotriol, D. Paricalcitol
C: Calcipotriol
Answer: C: Calcipotriol 
Explanation: Ans. is 'c' i.e., Calcipotriol VitDo It occurs mainly in two forms Vit D3 - Cholecalciferol - synthesized in skin under the influence of UV rays from 7-dehydrocholesterol.Vit D2 - Calciferol - present in irradiatiate food-yeast, fungi, bread,o Activation of Vit D takes place in following manner.o The final hydroxylation in the kidney by enzyme 1-a hydroxylase is the rate limiting step - enhanced by parathormone.o 1, 25 dihydroxy Vit D3 (calcitriol) is the active form of lit D3