Question 1

Q: Which of the following statements about the oral anticoagulant warfarin is incorrect?

Acts both in vivo and in vitro. ***Acts both in vivo and in vitro*** - This statement is incorrect because **warfarin** is an **oral anticoagulant** that acts **only in vivo** by inhibiting **vitamin K epoxide reductase**, thereby interfering with the synthesis of **vitamin K-dependent clotting factors (II, VII, IX, X)** in the liver [1, 2]. - Its mechanism requires metabolic processing by the body, meaning it has no direct anticoagulant effect on blood samples **in vitro** [1]. *Inhibits vitamin K epoxide reductase* - This statement is correct. **Warfarin's mechanism of action** involves inhibition of **vitamin K epoxide reductase (VKORC1)**, the enzyme responsible for regenerating the reduced form of **vitamin K** [1, 2]. - This prevents the **γ-carboxylation** of glutamate residues on **clotting factors II, VII, IX, and X**, rendering them biologically inactive [2]. *Acts only in vivo* - This statement is correct, as **warfarin's anticoagulant effect** is entirely dependent on its metabolism within the body to interfere with **coagulation factor synthesis** [1]. - It does not exert any direct anticoagulant effect if added to a blood sample in a test tube [1]. *Causes bleeding complications such as Hematuria* - This statement is correct. A common and significant side effect of **warfarin** is an increased risk of bleeding due to its **anticoagulant properties** [1]. - **Hematuria** (blood in the urine) is one of several potential bleeding complications (along with **epistaxis**, **gum bleeding**, or **gastrointestinal bleeding**) that can occur if the **anticoagulation level is excessive** [1].

Question

Which of the following statements about the oral anticoagulant warfarin is incorrect?

Accepted Answer

Acts both in vivo and in vitro

Answer

Inhibits vitamin K epoxide reductase

Answer

Acts only in vivo

Answer

Causes bleeding complications such as Hematuria

Drugs Affecting Blood and Blood Formation — MCQs

Drugs Affecting Blood and Blood Formation — MCQs

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