Explain the rationale for artemisinin-based combination therapy and describe the regimens used in India.

Rationale for Combination

The artemisinin component acts within hours and clears the great majority of parasites — reducing the biomass by about 10,000-fold per cycle → But its half-life is only 1–3 hours, so it is gone within a day → A residual population would survive and cause recrudescence → The long-acting partner persists for days to weeks and eliminates the remainder → Because the partner drug faces only a small residual parasite load, the chance of a resistant mutant surviving is very low → Each drug therefore protects the other from resistance

Regimens

Advantages and Adverse Effects

• Advantages — the most rapid parasite and fever clearance of any antimalarial; effective against multidrug-resistant strains; gametocidal, so they reduce transmission; short 3-day course; and well tolerated
• Adverse effects — generally mild: nausea, dizziness, anorexia
• Delayed haemolysis — occurring 1 to 3 weeks after intravenous artesunate for severe malaria, from delayed clearance of once-infected erythrocytes; haemoglobin should be checked at follow-up
• Neurotoxicity in animals at high dose has not been shown in humans at therapeutic doses
• Avoided in the first trimester of pregnancy where alternatives exist, though they are used when the alternative is severe malaria, which is far more dangerous to mother and fetus

Artemisinin Resistance

• First detected in the Greater Mekong region, and manifests as delayed parasite clearance rather than outright treatment failure
• Associated with mutations in the PfKELCH13 gene
• Partner drug resistance then causes actual failure, which is the real danger; combinations fail when both components are compromised
• Reports of kelch13 mutations from Africa and India are a serious concern, since there is no replacement class ready
• Containment — banning oral artemisinin monotherapy, ensuring quality of medicines (substandard and counterfeit antimalarials contribute directly), confirming diagnosis before treatment, and vector control

Applied Aspects

• Confirm the diagnosis before treating — presumptive treatment of every fever wastes drugs, delays the real diagnosis and accelerates resistance
• Give artemether-lumefantrine with food or milk; without fat, absorption is poor and treatment fails
• Complete the full 3-day course even though fever settles within a day; stopping early leaves the residual parasites that the partner drug was meant to clear
• Use intravenous artesunate for severe malaria, and do not delay it while awaiting confirmation in a strongly suspected case
• Check haemoglobin 1 to 3 weeks after intravenous artesunate, given the risk of delayed haemolysis
• Oral artemisinin monotherapy is banned in India and should never be prescribed or dispensed; it is the single practice most likely to destroy the usefulness of this class