Final answer:
Chloroquine is ineffective at preventing relapses in vivax and malariae malaria due to parasite resistance and because it doesn't target the liver stages of the parasites responsible for relapses. Primaquine from the 8-aminoquinolines class is more effective due to its ability to combat these dormant stages.
Step-by-step explanation:
Chloroquine does NOT prevent relapses in patients with vivax or malariae malaria primarily because of resistance to chloroquine in these types of malaria. Over time, the Plasmodium parasites that cause vivax and malariae malaria have developed mechanisms to evade the action of chloroquine, rendering it less effective. These resistance patterns emerged early on and have spread globally. Chloroquine is specifically unable to prevent relapses in vivax and malariae malaria due to its inability to target the dormant liver stages (hypnozoites) of these parasites, which are responsible for relapses. Instead, drugs like primaquine, which belong to the 8-aminoquinolines class, are effective at targeting these stages due to their unique mechanism of action, including anti-hypnozoite activity.