Antibiotics may affect gut flora, altering production of which vitamin essential for coagulation?

• A. Vitamin A
• B. Vitamin C
• C. Vitamin K
• D. Vitamin D

Answer: (C)

Antibiotics can disrupt the gut bacteria that normally produce vitamin K. This vitamin is essential for coagulation because it enables gamma-carboxylation of glutamate residues on clotting factors II, VII, IX, and X, as well as proteins C and S. Without enough vitamin K, these factors don’t become fully functional, leading to impaired clotting and a tendency to bleed.

Other vitamins don’t rely on gut bacteria for their role in coagulation. Vitamin A supports vision and mucous membranes, vitamin C is important for collagen synthesis and healing, and vitamin D helps with calcium metabolism. The connection to coagulation and antibiotic impact specifically points to vitamin K.