Drug used for chloroquine-resistant vivax malaria are all of the following except: September 2009
Chloroquine resistance in Plasmodium vivax is a known issue, especially in certain regions. The standard treatment for chloroquine-resistant vivax malaria usually includes artemisinin-based combination therapies (ACTs), like artemether-lumefantrine or artesunate-mefloquine. Also, primaquine is used to target the liver stage to prevent relapse. Quinine might be another option, though it's more for falciparum. Then there's tafenoquine as well.
Wait, the question is asking which drug is NOT used for chloroquine-resistant vivax. So the exception would be a drug that's not effective against resistant strains. Let's say the options include chloroquine itself. But chloroquine is ineffective in resistant cases, so if that's an option, it would be the correct answer. Alternatively, maybe a drug like mefloquine alone without artesunate? Or perhaps a drug that's not used at all for vivax, like doxycycline? Doxycycline is more for prophylaxis or as part of ACTs in some cases.
Wait, the correct answer here is probably chloroquine. Because if the options include chloroquine, then that's the one not used for resistant cases. Let me check standard treatment guidelines. For chloroquine-resistant P. vivax, ACTs are recommended. So chloroquine would be the exception here. So the correct answer is chloroquine. Therefore, the explanation should highlight that chloroquine is ineffective against resistant strains and thus not used, while the other options (like ACTs and primaquine) are used. The other wrong options would be drugs that are indeed used, so they are incorrect as exceptions.
**Core Concept**
Chloroquine-resistant *Plasmodium vivax* malaria requires alternative therapies due to loss of efficacy of chloroquine. Artemisinin-based combination therapies (ACTs) and drugs targeting hypnozoites (e.g., primaquine) are standard treatments. Chloroquine remains effective against non-resistant strains but fails in resistant cases.
**Why the Correct Answer is Right**
Chloroquine is the exception because it is ineffective against chloroquine-resistant *P. vivax*. Resistance arises via mutations in the *P. vivax* chloroquine resistance transporter (*PvCRT*), reducing intracellular drug accumulation. ACTs like artemether-lumefantrine or artesunate-mefloquine are first-line therapies, while primaquine eradicates dormant hypnozoites to prevent relapse.
**Why Each Wrong Option is Incorrect**
**Option A:** Artemisinin derivatives (e.g., artesunate) are effective against all *Plasmodium* species, including chloroquine-resistant *P. vivax*.
**Option B:** Mefloquine is part of ACTs (e.g., artesunate-mefloquine) for resistant *P. vivax*.
**Option C:** Primaquine is critical