**Question:** The drug which is contraindicated in haemophilia is

A. Heparin
B. Factor VIII concentrate
C. Factor IX concentrate
D. Platelet transfusion

**Core Concept:**

Haemophilia is a genetic disorder characterized by bleeding disorders due to deficiency or dysfunction of clotting factors (proteins) in the blood. The three main types of haemophilia are:

1. Haemophilia A: caused by deficiency of factor VIII;
2. Haemophilia B: caused by deficiency of factor IX;
3. Haemophilia C: caused by deficiency of factor XI.

**Why the Correct Answer is Right:**

The correct answer, Heparin, is a synthetic anticoagulant (blood thinner) that works by inhibiting factor Xa (converting enzyme) to prevent blood clot formation. In haemophilia patients, especially those with Haemophilia A (factor VIII deficiency), using Heparin would exacerbate the bleeding tendency due to its anticoagulant effect. As a result, Heparin is contraindicated in patients with haemophilia.

**Why Each Wrong Option is Incorrect:**

1. Factor VIII concentrate (Option B) and Factor IX concentrate (Option C) are used for the treatment of haemophilia A and B, respectively. In contrast, the correct answer (Heparin) is contraindicated in haemophilia patients.
2. Platelet transfusion (Option D) would be beneficial in haemophilia patients to increase platelet count and improve hemostasis, as platelets play a crucial role in blood clot formation. This option is unrelated to the issue of anticoagulant drugs in haemophilia patients.

**Clinical Pearl:**

Clotting factor concentrates, such as Factor VIII and Factor IX, are essential for the treatment of haemophilia A and B, respectively. In contrast, the use of Heparin, a potent anticoagulant, would worsen the bleeding tendency in haemophilia patients. This highlights the importance of considering individual patient conditions and history while choosing treatment options in medicine.