## Core Concept
The radical cure of *Plasmodium vivax* malaria involves targeting the dormant liver stages (hypnozoites) of the parasite to prevent relapse. This is crucial for eliminating the infection completely. The drugs used for radical cure must be effective against these liver stages.

## Why the Correct Answer is Right
The correct answer, **Primaquine**, is a well-known antimalarial drug specifically used for the radical cure of *P. vivax* and *P. ovale* infections. It works by killing the hypnozoites in the liver, thereby preventing future relapses. Primaquine is a 8-aminoquinoline derivative, and its mechanism involves interfering with the DNA synthesis of the parasite, ultimately leading to its death.

## Why Each Wrong Option is Incorrect
* **Option A: Chloroquine** - Chloroquine is effective against the blood stages of *P. vivax* but does not target the liver stages (hypnozoites), making it ineffective for radical cure.
* **Option B: Artemether** - Artemether is a fast-acting antimalarial that targets the blood stages of the parasite. It is not used for the radical cure of *P. vivax* as it does not affect the hypnozoites in the liver.
* **Option D: Mefloquine** - Mefloquine is another blood-stage antimalarial that is used for prophylaxis and treatment of malaria but does not have activity against the liver stages of *P. vivax*.

## Clinical Pearl / High-Yield Fact
A key point to remember is that primaquine can cause hemolysis, especially in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Therefore, screening for G6PD deficiency is recommended before administering primaquine for radical cure.

## Correct Answer: . Primaquine