PCR adjusted cure rates in clinical trials of antimalarial drugs in Africa : influence of extended follow-up and consecutive day blood sampling

Abstract

Malaria treatment guidelines are based primarily on results from clinical trials. Accurate assessment of drug efficacy in such studies therefore represents a prerequisite to ensure effective and lifesaving treatment for children with Plasmodium falciparum infections in Africa. The World Health Organization standard procedures for in vivo assessment include a patient follow-up duration of at least 28 days. However, during four weeks or more after initiation of treatment in high transmission areas in Africa recurrent infections are inevitable, due to the continuous exposure to infective mosquito bites. Since microscopy cannot distinguish parasites that have escaped drug action (treatment failure/recrudescence) from those arising from new mosquito inoculations (new infections/reinfections), polymerase chain reaction (PCR) based genotyping of malaria infections has been introduced to improve this distinction. PCR adjustment is presently achieved by analysis of two blood samples, one collected at enrolment and the other at time of recurrent parasitaemia. However, despite being a sensitive technique PCR may not identify minority clones in complex malaria infections and parasites sequestering in the deep vascular system during the later part of the erythrocytic life cycle.

This thesis primarily addresses two fundamental aspects of the assessment of PCR adjusted efficacy of antimalarial drugs in Africa, i.e. the influence of extended follow-up beyond 28 days and added consecutive day blood sampling.

The results reveal that both an extension of follow-up and consecutive day blood sampling improve the identification of recrudescences. By pooling data from 1414 children enrolled in three studies included in this thesis the overall sensitivity of the 28 day follow-up schedule to identify recrudescences was calculated to 48/72=67% [95% CI 55-76%] compared with day 42 assessment. Moreover, consecutive day, instead of single day blood sampling improved identification of recrudescences by circa 20%.

The work in this thesis also highlights the potential influence of the number of genetic markers used and the choice of DNA extraction method on the efficacy outcome in the clinical trials

Thus, assessment of PCR adjusted cure rates in high endemic areas depends substantially on methodology and should therefore be interpreted with caution. The results from this thesis should be considered in the design of antimalarial drug trials to improve assessment of antimalarial drug efficacy in Africa.