**Question:** Chemoprohylaxis of chloroquine includes -

A. Proguanil
B. Mefloquine
C. Primaquine
D. Quinine

**Core Concept:** Chemoprophylaxis is the prophylactic use of medications to prevent the occurrence or progression of an infectious disease. In the context of malaria chemoprophylaxis, chloroquine is a commonly used antimalarial drug.

**Why the Correct Answer is Right:** Chloroquine is a 4-aminoquinoline drug primarily targeting the parasite's glycolytic pathway. It works by inhibiting the parasite's enzyme 6-phosphogluconate dehydrogenase, which is essential for the parasite's growth and survival. Combining chloroquine with other drugs enhances its effectiveness and reduces the risk of resistance.

**Why Each Wrong Option is Incorrect:**

A. Proguanil: This drug is also an antimalarial, but it does not have a synergistic effect with chloroquine. Proguanil is a sulfonamide drug that works by inhibiting the parasite's dihydrofolate reductase enzyme.

B. Mefloquine: This drug is a type of quinoline antimalarial drug. While it is effective against chloroquine-resistant Plasmodium falciparum, its combination with chloroquine may lead to an increased risk of central nervous system toxicity.

C. Primaquine: This drug is a 8-aminoquinoline antimalarial and works by inducing hemozoin formation, which is toxic to the parasite. Primaquine is used to prevent relapses caused by hypnozoites in the liver. Combining chloroquine with primaquine enhances its efficacy, reducing the risk of chloroquine resistance.

D. Quinine: Quinine is an antimalarial drug primarily used for severe malaria treatment due to its ability to cross the blood-brain barrier. Combining chloroquine and quinine is not recommended, as it significantly increases the risk of severe side effects and toxicity, particularly in elderly individuals.

**Clinical Pearl:** Combining chloroquine with another antimalarial drug can enhance its effectiveness and reduce the risk of resistance. However, not all combinations are safe or recommended. Dosing, side effects, and patient factors should be taken into account when choosing an antimalarial drug for chemoprophylaxis.