The emergence and spread of resistance to antimalarial drugs threatens the efficacy of existing drug treatments. Parasite clearance rate (the rate at which parasitaemia declines) is an important measure of drug efficacy. It can be used to assess the in vivo responses to treatment with artemisinin derivatives, evaluate new antimalarial drugs and assess therapeutic response in severe malaria and hyperparasitaemia. A lag phase, which often precedes a fall in the parasite count, complicates the estimation of parasite clearance. This period must be identified by the observer, introducing subjectivity that may influence both the accuracy and consistency of results.  

Clear guidelines do not currently exist that define a consistent method of identifying resistance. This increases the need for an accurate and consistent method of clearance estimation, to allow data comparison between populations (see Figure below).  Only by comparison can prolonged clearance, an important early warning sign of resistance to artemisinin derivatives, be identified. To address this need, WWARN has developed the Parasite Clearance (PC) Estimator. Our aim is to provide the community with an accurate and consistent method of clearance estimation. PC Estimator uses a new approach to identify the lag phase, clean the data and fit the best model available to estimate the parasite clearance. Several measures of parasite clearance are calculated: clearance rate constant, slope half-life, PC50, PC90, PC95 and PC99.

Stylised graphs showing the distribution of parasite clearance half lives for two populations: population B shows evidence of prolonged clearance, when compared to population A.

See Flegg et al. 2011 Standardizing the measurement of parasite clearance in falciparum malaria: the parasite clearance estimator. Malaria Journal 10:339 doi:10.1186/1475-2875-10-339.