Large doses of vitamin K administered to a newborn result in: September 2012
**Core Concept**
Vitamin K is essential for the postnatal synthesis of clotting factors II, VII, IX, and X, which are necessary for the intrinsic and extrinsic pathways of blood coagulation. Newborns are at risk of vitamin K deficiency bleeding (VKDB) due to the low levels of vitamin K in their body.
**Why the Correct Answer is Right**
When large doses of vitamin K are administered to a newborn, it rapidly increases the levels of these clotting factors, thereby reducing the risk of VKDB. This is because vitamin K acts as a cofactor for the enzyme gamma-glutamyl carboxylase, which is necessary for the post-translational modification of these clotting factors. With sufficient vitamin K, these clotting factors are converted into their active forms, enabling normal blood coagulation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the administration of vitamin K in newborns.
**Option B:** Vitamin K administration does not affect the levels of clotting factors in a way that would lead to thrombosis.
**Option C:** There is no evidence to suggest that large doses of vitamin K in newborns would lead to an increased risk of cancer.
**Clinical Pearl / High-Yield Fact**
Newborns are at increased risk of bleeding due to vitamin K deficiency, which can be prevented with prophylactic vitamin K administration.
**Correct Answer: A. No adverse effects.**