**Question:** Dicumarol interferes with -

A. Vitamin K synthesis
B. Prothrombin synthesis
C. Factor VIII synthesis
D. Factor X synthesis

**Core Concept:**
Dicumarol is a vitamin K antagonist, a class of medications that inhibit the synthesis and function of clotting factors (coagulation cascade proteins) dependent on vitamin K. Vitamin K is essential for post-glutamic carboxylation of proteins like Factors II, VII, IX, X, Protein C, Protein S, and Mixed Inhibitor Concentration (MIC).

**Why the Correct Answer is Right:**
Dicumarol primarily targets the synthesis of clotting factors II (prothrombin), VII, IX, and X, which are dependent on vitamin K. It interferes with the gamma-carboxylation of these clotting factors, impairing their function.

**Why Each Wrong Option is Incorrect:**
A. Vitamin K synthesis is not directly targeted by dicumarol; however, it indirectly affects vitamin K levels, leading to reduced availability for clotting factors.
B. Prothrombin synthesis is directly affected by dicumarol, which disrupts the gamma-carboxylation of prothrombin, resulting in impaired clotting function.
C. Factor VIII synthesis is not targeted by dicumarol; instead, it affects the availability of vitamin K, indirectly influencing Factor VIII synthesis.
D. Factor X synthesis is directly affected by dicumarol, causing impaired gamma-carboxylation and reduced Functional activity of factor X.

**Clinical Pearl:**
Understanding the effects of vitamin K antagonists like dicumarol is essential in managing patients on these medications, particularly in situations like major surgery, trauma, or excessive blood loss. Clinicians should monitor coagulation parameters and consider switching to a vitamin K agonist (e.g., warfarin) if indicated.

**Correct Answer:** B. Prothrombin synthesis