**Core Concept**
P. vivax infection can relapse due to the persistence of hypnozoites in the liver, which require a specific drug for their eradication. The ideal drug should target these dormant forms and prevent the recurrence of the infection.

**Why the Correct Answer is Right**
Primaquine is a 8-aminoquinoline that is effective against the hypnozoites of P. vivax and P. ovale. It is the only drug that can eliminate these dormant forms from the liver, thereby preventing the relapse of the infection. Primaquine works by generating reactive oxygen species that damage the DNA of the hypnozoites, ultimately leading to their death. This mechanism makes primaquine an essential component in the treatment of P. vivax malaria.

**Why Each Wrong Option is Incorrect**
**Option A:** Chloroquine is effective against the blood stages of P. vivax but has no activity against the hypnozoites.
**Option B:** Artemisinin-based combination therapies are used to treat the acute attack of P. vivax malaria but do not prevent relapse.
**Option C:** Mefloquine is used for the prophylaxis and treatment of P. falciparum malaria, but it is not effective against the hypnozoites of P. vivax.

**Clinical Pearl / High-Yield Fact**
Primaquine should be used with caution in patients with G6PD deficiency, as it can cause hemolysis. A G6PD level should be checked before initiating primaquine therapy, and the patient should be monitored for signs of hemolysis.

**Correct Answer: C. Primaquine**