## Mechanism of Action and Pharmacokinetics of Antimalarials ### Why Option 3 (Mefloquine Absorption) is INCORRECT **Key Point:** Mefloquine has a SLOW and ERRATIC absorption profile with peak plasma concentrations occurring 6–24 hours (often 12–18 hours) after oral administration. This delayed absorption makes it unsuitable for acute malaria treatment and explains why it is reserved for prophylaxis or non-severe malaria in resource-limited settings. **High-Yield:** Mefloquine's slow absorption and long half-life (~3 weeks) are why it causes delayed neuropsychiatric side effects and why loading doses are sometimes used in prophylaxis protocols. ### Why the Other Options are CORRECT | Drug | Mechanism | Pharmacokinetic Feature | |------|-----------|------------------------| | Chloroquine | Inhibits heme polymerase → prevents detoxification of toxic heme | Accumulates in parasitized RBCs; high tissue affinity | | Artemisinin | Generates ROS via Fe²⁺ interaction → rapid parasite death | Fast-acting; used in severe malaria | | Atovaquone-proguanil | Synergistic: mitochondrial ETC inhibition + DHFR inhibition | Rapid onset; suitable for treatment and prophylaxis | **Clinical Pearl:** The slow absorption of mefloquine is clinically important—it cannot be used for acute severe malaria management, where artemisinin derivatives or IV artesunate are required. **Tip:** When comparing antimalarials on exams, always check absorption kinetics: chloroquine (rapid), artemisinin (very rapid), atovaquone-proguanil (rapid), mefloquine (SLOW—the outlier).
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