Explain the treatment ( type of malaria, it's treatment drug , dose, duration, mechanism of action etc) explain this in detailed notes
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Treatment of Malaria - Detailed Notes
Sources: Katzung's Basic and Clinical Pharmacology 16e, Goldman-Cecil Medicine, Park's Textbook of Preventive and Social Medicine, Goodman & Gilman's Pharmacological Basis of Therapeutics
1. Overview of Malaria Species and Treatment Approach
There are five Plasmodium species that infect humans. Treatment depends on:
- Species (determines drug choice)
- Severity (uncomplicated vs. severe/complicated)
- Geographic resistance pattern (chloroquine-sensitive vs. resistant areas)
- Special population (pregnancy, children, G6PD deficiency)
| Species | Clinical Notes | Key Treatment Feature |
|---|---|---|
| P. falciparum | Most dangerous; causes severe malaria | ACT first-line; chloroquine resistance widespread |
| P. vivax | Relapses due to hypnozoites | Chloroquine + Primaquine (radical cure) |
| P. ovale | Relapses due to hypnozoites | Chloroquine + Primaquine |
| P. malariae | Quartan fever; no relapses | Chloroquine alone |
| P. knowlesi | Zoonotic; rapid parasite doubling | Treated like P. falciparum |
2. Treatment of P. vivax Malaria
First-Line: Chloroquine + Primaquine
Why two drugs?
- Chloroquine kills blood-stage (erythrocytic) parasites
- Primaquine kills dormant liver forms (hypnozoites) - prevents relapses (relapse rate ~30% without it)
A. Chloroquine
| Parameter | Details |
|---|---|
| Drug class | 4-aminoquinoline |
| Dose | 25 mg/kg body weight total over 3 days: 10 mg/kg Day 1, 10 mg/kg Day 2, 5 mg/kg Day 3 |
| Adult dose | 600 mg base (4 tabs) Day 1, 600 mg Day 2, 300 mg (2 tabs) Day 3 |
| Duration | 3 days |
| Route | Oral |
| Formulation | Chloroquine phosphate; each tablet = 150 mg base |
Mechanism of Action:
Chloroquine concentrates in the parasite's food vacuoles. Inside the vacuole, the parasite digests haemoglobin and releases toxic free haeme (ferriprotoporphyrin IX). Normally, the parasite detoxifies this by polymerizing it into insoluble crystalline haemozoin. Chloroquine inhibits haeme polymerization (haeme crystallization), causing buildup of free toxic haeme, which damages parasite membranes and kills the parasite.
Resistance mechanism: Mutations in PfCRT (P. falciparum chloroquine resistance transporter) actively pump chloroquine out of the food vacuole, preventing lethal haeme accumulation. Resistance is now very widespread in P. falciparum but uncommon in P. vivax (except parts of Papua New Guinea and Indonesia).
Pharmacokinetics:
- Rapidly and almost completely absorbed from GI tract
- Peak plasma levels in ~3 hours
- Very large volume of distribution (100-1000 L/kg) - binds extensively to tissues
- Initial half-life: 3-5 days; terminal half-life: 1-2 months
- Principally excreted in urine
Adverse effects: Generally well tolerated. Pruritus (common in Africans), nausea, vomiting, abdominal pain, headache, blurred vision. Rarely: retinopathy (with long-term high doses), QT prolongation, cardiac toxicity.
B. Primaquine (Radical Cure - Anti-relapse)
| Parameter | Details |
|---|---|
| Drug class | 8-aminoquinoline |
| Dose | 0.25 mg/kg/day for 14 days |
| Adult dose | 15 mg base daily for 14 days (standard); WHO recommends 30 mg base for 14 days |
| Duration | 14 days |
| Route | Oral |
| Target | Liver hypnozoites (dormant forms) |
Mechanism of Action:
Primaquine is converted in the body to reactive metabolites that interfere with the parasite's mitochondrial electron transport chain, generating reactive oxygen species (ROS). This causes oxidative damage to hypnozoites and gametocytes. It is the only drug (along with tafenoquine) that kills hepatic hypnozoites and thus achieves radical cure.
Contraindications:
- G6PD deficiency - Can cause severe haemolytic anaemia (check G6PD before prescribing)
- Pregnancy - Absolutely contraindicated
- Infants - Contraindicated
Warning signs for haemolysis: Dark urine, jaundice, abdominal pain, nausea - stop drug immediately and report.
Dosage Chart for P. vivax (India - Park's Textbook)
| Age | Day 1 CQ (150mg base) | Day 2 CQ | Day 3 CQ | Primaquine (2.5mg) Day 1-14 |
|---|---|---|---|---|
| <1 year | ½ tab | ½ tab | ¼ tab | 0 (contraindicated) |
| 1-4 years | 1 tab | 1 tab | ½ tab | 1 tab daily |
| 5-8 years | 2 tabs | 2 tabs | 1 tab | 2 tabs daily |
| 9-14 years | 3 tabs | 3 tabs | 1½ tabs | 4 tabs daily |
| ≥15 years | 4 tabs | 4 tabs | 2 tabs | 6 tabs daily |
| Pregnancy | 4 tabs | 4 tabs | 2 tabs | NOT given |
Alternative: Tafenoquine (Single-Dose Radical Cure)
- Dose: 300 mg single dose (after chloroquine therapy)
- Advantage: Single dose vs. 14-day primaquine regimen - greatly improves adherence
- Same contraindication: G6PD deficiency testing mandatory before use
- Similar mechanism to primaquine - targets hypnozoites via oxidative stress
3. Treatment of P. falciparum Malaria
A. Uncomplicated P. falciparum
First-line: Artemisinin-Based Combination Therapy (ACT)
WHO recommends ACT as the universal first-line treatment for uncomplicated P. falciparum malaria. Monotherapy with artemisinins is banned/discouraged globally to prevent resistance.
Key ACT Regimens
1. Artemether-Lumefantrine (Coartem / Riamet) - Most widely used worldwide
| Parameter | Details |
|---|---|
| Formulation | Artemether 20 mg + Lumefantrine 120 mg (co-formulated tablet) |
| Dose (adult) | 4 tablets twice daily for 3 days (total 6 doses over 72 hours) |
| Duration | 3 days |
| Route | Oral |
| Special instruction | Must be taken WITH food (increases lumefantrine absorption 16-fold) |
| FDA approval | Yes (only ACT approved in the USA) |
| Use in India (NE states) | Age-specific ACT-AL; not recommended <5 kg or first trimester |
Mechanism of Action:
- Artemether: Sesquiterpene lactone endoperoxide. Activated by intraparasitic iron (haeme iron) via Fenton reaction, generating carbon-centred free radicals. These free radicals alkylate and damage parasite proteins and membranes, inhibit mitochondrial function, and cause rapid death of asexual blood-stage parasites. Acts rapidly (within hours) and reduces parasite biomass by ~10,000-fold per cycle.
- Lumefantrine: A fluorene derivative. Mechanism shares some similarities with chloroquine - inhibits haeme polymerization and disrupts parasite membrane function. Has a longer half-life (~3-6 days), which clears residual parasites after the artemether component is eliminated.
Adverse effects: Headache, anorexia, dizziness, asthenia, arthralgia, myalgia. QT interval prolongation (lumefantrine) - contraindicated if abnormal QTc. Lumefantrine inhibits CYP2D6.
2. Artesunate + Sulfadoxine-Pyrimethamine (ACT-SP) - First-line in India (non-NE states)
| Parameter | Details |
|---|---|
| Artesunate dose | 4 mg/kg/day for 3 days (50 mg tablets) |
| SP dose | Single dose on Day 1: Sulfadoxine 25 mg/kg + Pyrimethamine 1.25 mg/kg |
| Primaquine | Single dose 0.75 mg/kg on Day 2 (gametocytocidal) |
| Duration | 3 days ACT + single dose SP |
Mechanism of SP (Sulfadoxine-Pyrimethamine):
- Sulfadoxine: Competitive inhibitor of dihydropteroate synthase (DHPS) - blocks folate synthesis (similar mechanism to sulfonamides)
- Pyrimethamine: Inhibits dihydrofolate reductase (DHFR) - blocks conversion of dihydrofolate to tetrahydrofolate, thus blocking DNA synthesis
- Double sequential blockade of folate pathway = synergistic effect
- Resistance is common in NE India and many parts of Africa (hence AL is used in those areas)
3. Artesunate + Amodiaquine (ASAQ)
- First-line in many African countries
- Amodiaquine shares mechanism with chloroquine (haeme polymerization inhibitor) but active against many chloroquine-resistant strains
4. Dihydroartemisinin + Piperaquine (DHA-PPQ)
- Highly effective; used in several countries
- Piperaquine: bisquinoline; mechanism similar to chloroquine
- Resistance has emerged in parts of SE Asia (kelch13 mutations + piperaquine resistance)
5. Atovaquone-Proguanil (Malarone)
| Parameter | Details |
|---|---|
| Formulation | Atovaquone 250 mg + Proguanil 100 mg per tablet |
| Dose (adult) | 4 tablets daily for 3 days |
| Route | Oral (take with fatty food - increases absorption) |
| Use | Treatment AND prophylaxis of P. falciparum; approved in USA |
Mechanism of Action:
- Atovaquone: Hydroxynaphthoquinone. Disrupts mitochondrial electron transport by binding cytochrome bc1 complex (ubiquinol-cytochrome c oxidoreductase). This collapses the mitochondrial membrane potential and blocks pyrimidine biosynthesis in the parasite (Plasmodium cannot salvage pyrimidines, unlike humans). Active against both tissue and blood schizonts.
- Proguanil: A biguanide prodrug, converted to active metabolite cycloguanil which inhibits DHFR (same target as pyrimethamine). Independently, proguanil (non-cycloguanil pathway) potentiates atovaquone's disruption of mitochondrial membrane potential.
- Together: powerful synergistic disruption of parasite mitochondria + folate pathway.
Key advantage: Active against tissue schizonts; chemoprophylaxis can be stopped only 1 week post-exposure (vs. 4 weeks for mefloquine/doxycycline).
Adverse effects: GI symptoms (nausea, vomiting, diarrhea, abdominal pain), headache, mouth ulcers. Reversible elevated liver enzymes.
B. Quinine-Based Regimens (Chloroquine-Resistant P. falciparum)
| Parameter | Details |
|---|---|
| Quinine sulfate dose | 650 mg 3 times daily for 3-7 days (oral) |
| Combined with | Doxycycline 100 mg twice daily for 7 days OR Clindamycin 600 mg twice daily for 7 days |
| Combined regimen duration | Quinine 3 days + doxycycline 7 days (if 3-day quinine), or full 7-day quinine |
Mechanism of Action:
Quinine is a quinoline alkaloid from Cinchona bark. It concentrates in parasite food vacuoles and inhibits haeme polymerization (similar to chloroquine). It is also believed to intercalate into parasite DNA. It has blood schizonticide activity against all species. Additionally stimulates insulin secretion.
Adverse effects (Cinchonism): Tinnitus, headache, nausea, dizziness, flushing, visual disturbances. Severe: haemolysis, hypoglycaemia, QT prolongation, blackwater fever (rare, severe haemolysis). Stimulates uterine contractions (use cautiously in pregnancy - however still used in first trimester severe malaria).
Doxycycline/Tetracycline mechanism: Inhibits parasite protein synthesis by binding 30S ribosomal subunit. Too slow to use alone - combined with quinine to shorten course and limit quinine toxicity.
C. Mefloquine
| Parameter | Details |
|---|---|
| Dose (treatment) | 750 mg then 500 mg 6-8 hours later OR single dose 1250 mg |
| Use | Chloroquine-resistant P. falciparum; also prophylaxis |
| Duration | Single day (split dose) |
Mechanism: Quinoline methanol compound. Mechanism not fully established - likely interferes with haeme detoxification and disrupts membrane function. Active blood schizonticide.
Adverse effects: Neurological (dizziness, nightmares, anxiety, psychosis, seizures) and GI toxicity are significant limitations. Contraindicated in persons with psychiatric illness or seizure disorders.
4. Severe (Complicated) Malaria
Severe malaria is a medical emergency - parenteral treatment is mandatory.
WHO Criteria for Severe Malaria (P. falciparum)
- Impaired consciousness/coma (cerebral malaria)
- Repeated generalized convulsions
- Renal failure (serum creatinine >3 mg/dl)
- Jaundice (serum bilirubin >3 mg/dl)
- Severe anaemia (Hb <5 g/dl)
- Pulmonary oedema / ARDS
- Hypoglycaemia (plasma glucose <40 mg/dl)
- Metabolic acidosis
- Circulatory collapse/shock (SBP <80 mmHg)
- Abnormal bleeding / DIC
- Haemoglobinuria
- Hyperthermia (>42°C)
- Hyperparasitaemia (>5-10% parasitized RBCs)
First-Line Parenteral Treatment: IV Artesunate
| Parameter | Details |
|---|---|
| Drug | Artesunate (water-soluble artemisinin derivative) |
| Dose | 2.4 mg/kg IV (or IM) at 0 hours, 12 hours, 24 hours; then once daily |
| Duration | Parenteral for minimum 24 hours, then switch to oral ACT |
| Route | IV infusion (preferred) or IM |
| Evidence | Superior to quinine in RCTs (lower mortality, faster parasite clearance) |
After parenteral phase: Switch to full course oral ACT (area-specific AL or ACT-SP for 3 days).
Mechanism of IV Artesunate:
Same as artemether (endoperoxide bridge cleavage by intraparasitic iron → free radicals → alkylation of parasite proteins and membranes). Artesunate is water-soluble (unlike artemether), making it suitable for IV administration. Rapidly converted to active metabolite dihydroartemisinin (DHA), which is the primary active compound.
Special note on delayed haemolysis: Can occur up to 4 weeks after IV artesunate therapy (unrelated to G6PD deficiency) - monitor post-treatment.
Alternative Parenteral: Intramuscular Artemether
| Parameter | Details |
|---|---|
| Dose | 3.2 mg/kg IM loading dose on Day 1, then 1.6 mg/kg/day |
| Use | Where IV access not available; good efficacy |
Alternative Parenteral: Quinine IV (if artesunate unavailable)
| Parameter | Details |
|---|---|
| Loading dose | 20 mg quinine salt/kg IV infusion over 4 hours |
| Maintenance | 10 mg/kg every 8 hours |
| Infusion rate | Must not exceed 5 mg/kg/hour |
| Cardiac monitoring | Mandatory (QT prolongation risk) |
| Follow-up oral | Quinine 10 mg/kg 3x/day + Doxycycline 100 mg/day to complete 7 days total |
5. Special Situations
Malaria in Pregnancy
| Trimester | P. falciparum Treatment | P. vivax Treatment |
|---|---|---|
| 1st trimester | Quinine + Clindamycin (ACT avoided in 1st trimester) | Chloroquine (NO primaquine) |
| 2nd & 3rd trimester | ACT (artemether-lumefantrine or ACT-SP) | Chloroquine |
| Severe malaria (any trimester) | IV artesunate preferred (does not worsen hypoglycaemia unlike quinine) | - |
- Primaquine is absolutely contraindicated in pregnancy
- Artemisinin derivatives preferred over quinine for severe disease in pregnancy (quinine worsens hypoglycaemia, stimulates contractions in 3rd trimester)
Mixed Infections (P. vivax + P. falciparum)
- Treat as P. falciparum: Full course ACT + Primaquine 0.25 mg/kg/day for 14 days
- NE states: ACT-AL 3 days + Primaquine 14 days
- Other states: ACT-SP 3 days + Primaquine 14 days
Treatment of P. ovale and P. malariae
- P. ovale: Treat as P. vivax (Chloroquine + Primaquine 14 days)
- P. malariae: Treat as P. falciparum (Chloroquine - usually sensitive; no primaquine needed as no hypnozoites)
6. Chemoprophylaxis Summary
| Drug | Regimen | Coverage | Notes |
|---|---|---|---|
| Chloroquine | 300 mg base weekly (start 1-2 wks before, continue 4 wks after) | Chloroquine-sensitive areas only | Drug of choice for prophylaxis in sensitive areas |
| Atovaquone-Proguanil (Malarone) | 1 adult tab daily | P. falciparum and others | Start 1-2 days before; stop 7 days after. Most convenient |
| Mefloquine | 250 mg once weekly | P. falciparum (most) | Start 2-3 wks before; continue 4 wks after; neuropsychiatric side effects |
| Doxycycline | 100 mg daily | P. falciparum (resistant areas SE Asia) | Start 1-2 days before; stop 4 wks after. Photosensitivity |
| Primaquine | 30 mg base daily | P. vivax/ovale; some P. falciparum | G6PD testing mandatory |
7. Drug Resistance
| Drug | Species | Mechanism of Resistance |
|---|---|---|
| Chloroquine | P. falciparum (widespread), P. vivax (SE Asia) | PfCRT mutations → efflux pump |
| SP (Sulfadoxine-Pyrimethamine) | P. falciparum | DHFR and DHPS point mutations |
| Artemisinins | P. falciparum (SE Asia, now East Africa) | Kelch13 (K13) gene mutations → delayed ring-stage parasite clearance |
| Mefloquine | P. falciparum (SE Asia) | Amplification of pfmdr1 gene |
8. Summary Table: Drug - Type - Dose - Duration - Mechanism
| Drug | Target Stage | Mechanism | Dose (Adult) | Duration |
|---|---|---|---|---|
| Chloroquine | Blood schizonts | Inhibits haeme polymerization in food vacuole | 600/600/300 mg base oral | 3 days |
| Primaquine | Hypnozoites + gametocytes | Oxidative stress on parasite mitochondria (via ROS) | 15-30 mg base/day oral | 14 days |
| Tafenoquine | Hypnozoites + gametocytes | Similar to primaquine | 300 mg single dose | 1 day |
| Artemisinins (artesunate, artemether, DHA) | Asexual blood stages (all); young gametocytes | Iron-catalysed free radical generation via endoperoxide cleavage → alkylates parasite proteins | 2.4 mg/kg IV (artesunate, severe); oral ACT (uncomplicated) | 3 days (oral); 1-7 days (IV) |
| Lumefantrine | Blood schizonts | Inhibits haeme polymerization; membrane disruption | In Coartem (with artemether) | 3 days |
| Sulfadoxine | Blood schizonts | Inhibits DHPS (folate synthesis) | 1500 mg single dose (with AS) | 1 day |
| Pyrimethamine | Blood schizonts | Inhibits DHFR (folate synthesis) | 75 mg (with sulfadoxine) | 1 day |
| Atovaquone | Blood + tissue schizonts | Inhibits mitochondrial cytochrome bc1 complex | 1000 mg/day (with proguanil) | 3 days |
| Proguanil | Blood + tissue schizonts | Prodrug → cycloguanil; inhibits DHFR; potentiates atovaquone | 400 mg/day (with atovaquone) | 3 days |
| Quinine | Blood schizonts | Inhibits haeme polymerization + DNA intercalation | 650 mg 3x/day oral; 20 mg/kg IV loading | 7 days oral / IV until tolerable |
| Doxycycline | Blood schizonts | Inhibits 30S ribosomal protein synthesis in parasite apicoplast | 100 mg 2x/day | 7 days (with quinine) |
| Mefloquine | Blood schizonts | Haeme polymerization disruption; membrane effects | 750 mg + 500 mg (split dose) | 1 day |
Sources:
- Katzung's Basic and Clinical Pharmacology, 16e (Chapter 52)
- Goldman-Cecil Medicine, International Edition (Chapter 316)
- Park's Textbook of Preventive and Social Medicine (Chapter on Malaria)
- Goodman & Gilman's Pharmacological Basis of Therapeutics, 14e (Chapter 66)
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