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The current method used to identify resistance to the antimalarial drug artemisinin is not entirely accurate, according to research published in PLOS Medicine.
Artemisinin rapidly clears malaria parasites from the blood of infected patients. When parasites develop resistance, clearance takes longer.
The best measure of parasite clearance is the parasite half-life in a patient’s blood, and a common cutoff used to denote artemisinin resistance is 5 hours.
Study author Lisa White, of Mahidol University in Bangkok, Thailand, and her colleagues found that parasite half-life predicts the likelihood of an artemisinin-resistant infection for individual patients. But the half-life is influenced by how common resistance is in the particular area.
The critical half-life varied between 3.5 hours in areas where resistance is rare to 5.5 hours in areas where resistance is common. This means there is no universal cutoff value in parasite half-life that can determine whether a particular infection is “sensitive” or “resistant” to artemisinin-based combination (ACT) therapy.
Because measuring the parasite half-life requires frequent blood sampling that is difficult to do in resource-limited settings, the World Health Organization (WHO) uses the following working definition for surveillance. Artemisinin resistance in a population is suspected if more than 10% of patients are still carrying parasites 3 days after the start of ACT.
Arguing that the cutoff used in the WHO’s working definition is based on limited data, the researchers examined how well the definition matches actual data from patients in areas with artemisinin-resistant parasites.
Applying a model specifically developed for this purpose, the team found that the WHO’s day-3 cutoff value of 10% is useful, but it would be more informative if the parasite load at the start of ACT was taken into account.
The researchers concluded that the WHO definition alone cannot be used to accurately predict the real proportion of artemisinin-resistant parasites, so a more detailed assessment is needed. 
Photo by Juan D. Alfonso
The current method used to identify resistance to the antimalarial drug artemisinin is not entirely accurate, according to research published in PLOS Medicine.
Artemisinin rapidly clears malaria parasites from the blood of infected patients. When parasites develop resistance, clearance takes longer.
The best measure of parasite clearance is the parasite half-life in a patient’s blood, and a common cutoff used to denote artemisinin resistance is 5 hours.
Study author Lisa White, of Mahidol University in Bangkok, Thailand, and her colleagues found that parasite half-life predicts the likelihood of an artemisinin-resistant infection for individual patients. But the half-life is influenced by how common resistance is in the particular area.
The critical half-life varied between 3.5 hours in areas where resistance is rare to 5.5 hours in areas where resistance is common. This means there is no universal cutoff value in parasite half-life that can determine whether a particular infection is “sensitive” or “resistant” to artemisinin-based combination (ACT) therapy.
Because measuring the parasite half-life requires frequent blood sampling that is difficult to do in resource-limited settings, the World Health Organization (WHO) uses the following working definition for surveillance. Artemisinin resistance in a population is suspected if more than 10% of patients are still carrying parasites 3 days after the start of ACT.
Arguing that the cutoff used in the WHO’s working definition is based on limited data, the researchers examined how well the definition matches actual data from patients in areas with artemisinin-resistant parasites.
Applying a model specifically developed for this purpose, the team found that the WHO’s day-3 cutoff value of 10% is useful, but it would be more informative if the parasite load at the start of ACT was taken into account.
The researchers concluded that the WHO definition alone cannot be used to accurately predict the real proportion of artemisinin-resistant parasites, so a more detailed assessment is needed.
Photo by Juan D. Alfonso
The current method used to identify resistance to the antimalarial drug artemisinin is not entirely accurate, according to research published in PLOS Medicine.
Artemisinin rapidly clears malaria parasites from the blood of infected patients. When parasites develop resistance, clearance takes longer.
The best measure of parasite clearance is the parasite half-life in a patient’s blood, and a common cutoff used to denote artemisinin resistance is 5 hours.
Study author Lisa White, of Mahidol University in Bangkok, Thailand, and her colleagues found that parasite half-life predicts the likelihood of an artemisinin-resistant infection for individual patients. But the half-life is influenced by how common resistance is in the particular area.
The critical half-life varied between 3.5 hours in areas where resistance is rare to 5.5 hours in areas where resistance is common. This means there is no universal cutoff value in parasite half-life that can determine whether a particular infection is “sensitive” or “resistant” to artemisinin-based combination (ACT) therapy.
Because measuring the parasite half-life requires frequent blood sampling that is difficult to do in resource-limited settings, the World Health Organization (WHO) uses the following working definition for surveillance. Artemisinin resistance in a population is suspected if more than 10% of patients are still carrying parasites 3 days after the start of ACT.
Arguing that the cutoff used in the WHO’s working definition is based on limited data, the researchers examined how well the definition matches actual data from patients in areas with artemisinin-resistant parasites.
Applying a model specifically developed for this purpose, the team found that the WHO’s day-3 cutoff value of 10% is useful, but it would be more informative if the parasite load at the start of ACT was taken into account.
The researchers concluded that the WHO definition alone cannot be used to accurately predict the real proportion of artemisinin-resistant parasites, so a more detailed assessment is needed.