Malaria is a mosquito-borne disease caused by Plasmodium species, mainly P. falciparum, P. vivax, P. malariae, P. ovale, and P. knowlesi. Because malaria parasites live inside human red blood cells and liver cells, treatment requires medicines that can target different stages of the parasite’s life cycle. Modern therapy focuses on fast parasite clearance and preventing treatment resistance.
Life Cycle of the Malaria Parasite (Simplified)
Understanding the life cycle helps in selecting the right drugs:
- Liver (hepatic) stage: parasites multiply silently
- Blood (erythrocytic) stage: causes fever and symptoms
- Dormant liver stage (hypnozoites): seen in P. vivax and P. ovale, causing relapses
Different antimalarial drugs act on different stages.
Classification of Antimalarial Drugs
1. Blood Schizonticides (Act on blood stage)
- Chloroquine
- Artemisinin derivatives (artesunate, artemether)
- Quinine and quinidine
- Mefloquine
- Atovaquone–proguanil
- Doxycycline
2. Tissue Schizonticides (Act on liver stage)
- Primaquine
- Atovaquone–proguanil
3. Gametocytocidal Drugs (Block transmission)
- Primaquine
- Artemisinin derivatives
Common Antimalarial Drugs
Chloroquine
Once the mainstay of malaria treatment, chloroquine kills blood-stage parasites by blocking heme detoxification. It is still useful for chloroquine-sensitive malaria, but widespread resistance limits its use.
Side Effects
- Nausea, vomiting
- Itching (common in dark-skinned individuals)
- Rarely, eye and heart toxicity with long-term use
Artemisinin-Based Combination Therapy (ACT)
ACT is the first-line treatment for P. falciparum malaria worldwide. It pairs a fast-acting artemisinin drug with a slower-acting partner drug to prevent resistance.
Common ACT Combinations
- Artemether + Lumefantrine (widely used)
- Artesunate + Sulfadoxine–Pyrimethamine
- Artesunate + Mefloquine
- Artesunate + Amodiaquine
Quinine and Quinidine
Used when ACT is not available or in severe malaria.
Side Effects
- Tinnitus (“ringing in ears”)
- Headache
- Low blood sugar (common in pregnancy)
Mefloquine
Used for treatment and prophylaxis.
Side Effects
- Nightmares
- Insomnia
- Mood changes
Primaquine
The only drug effective against dormant liver stages (hypnozoites) of P. vivax and P. ovale. Prevents relapse.
Warning
Not safe in G6PD deficiency → can cause hemolysis.
Atovaquone–Proguanil
Effective against both liver and blood stages. Used for treatment and malaria prevention during travel.
Treatment of Uncomplicated Malaria
1. P. falciparum (drug-resistant)
ACT for 3 days is recommended worldwide.
2. P. vivax and P. ovale
- Chloroquine (if sensitive)
- Primaquine for 14 days to prevent relapse
3. P. malariae and P. knowlesi
Chloroquine or ACT is effective.
Treatment of Severe Malaria
- IV artesunate (preferred)
- IV quinine (alternative)
Supportive care is essential: fluids, oxygen, glucose monitoring, and treating complications.
Malaria Prophylaxis (Prevention)
Recommended for travellers to malaria-endemic areas.
Common Options
- Mefloquine – weekly
- Doxycycline – daily
- Atovaquone–Proguanil – daily
Side Effects of Antimalarial Drugs (General)
- Nausea, vomiting
- Headache and dizziness
- Allergic reactions
- Neurological problems (mefloquine)
- Hemolysis in G6PD deficiency (primaquine)
Drug Resistance
Resistance is a major global concern, especially with chloroquine and sulfadoxine-pyrimethamine.
Causes
- Incorrect dosing
- Incomplete treatment
- Widespread drug misuse
ACTs help delay resistance by combining two drugs with different mechanisms.
Detailed Notes:
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