Dose-dependent risk of neutropenia after 7-day courses of artesunate monotherapy in Cambodian patients with acute Plasmodium falciparum malaria.

BACKGROUND: Fears of emerging artemisinin resistance in western Cambodia have prompted a series of clinical trials investigating whether slow responses to antimalarial treatment can be overcome by increasing doses of drug. METHODS: Patients with uncomplicated malaria were allocated 1 of 3 oral artesunate monotherapy regimens (2, 4, or 6 mg/kg/day for 7 days) and were observed for 42 days. A series of safety measures, including complete blood count on days 0, 3, 6, and 14, was implemented because of a lack of safety data for these experimental doses. RESULTS: After 3 doses, geometric mean absolute neutrophil counts were reduced in all groups, and 2 patients required artesunate to be discontinued because of neutropenia (absolute neutrophil count, <1.0 × 10(3) cells/µL). Recipients of the 6 mg/kg/day dosage had significantly lower geometric mean absolute neutrophil counts than did recipients of the 2 and 4 mg/kg/day dosages at 6 and 14 days (P < .001 for each). Overall, 5 (19%) of 26 patients who received the 6 mg/kg/day dosage became neutropenic within 14 days, triggering a cohort-halting rule and ending the trial early. Pharmacokinetic data from neutropenic patients showed wide variance, with plasma clearance occurring significantly slower in neutropenic patients than in nonneutropenic patients. CONCLUSIONS: Artesunate remains a crucial drug for the treatment of malaria, and determining optimal dosing regimens is vital to overcome emerging resistant parasite strains along the Thai-Cambodian border. However, future experimental dosing studies must be designed with care, because the safety of such regimens can no longer be assumed. The artemisinin derivatives remain one of the safest classes of antimalarial drugs, but this study demonstrates that the dosing limit may have been reached.

Artesunate dose escalation for the treatment of uncomplicated malaria in a region of reported artemisinin resistance: a randomized clinical trial.

BACKGROUND: The emergence of artemisinin resistance has raised concerns that the most potent antimalarial drug may be under threat. The currently recommended daily dose of artesunate (AS) is 4 mg/kg, and is administered for 3 days together with a partner antimalarial drug. This study investigated the impact of different AS doses on clinical and parasitological responses in malaria patients from an area of known artemisinin resistance in western Cambodia. METHODS: Adult patients with uncomplicated P. falciparum malaria were randomized into one of three 7-day AS monotherapy regimens: 2, 4 or 6 mg/kg/day (total dose 14, 28 and 42 mg/kg). Clinical, parasitological, pharmacokinetic and in vitro drug sensitivity data was collected over a 7-day inpatient period and during weekly follow-up to 42 days. RESULTS: 143 patients were enrolled (n = 75, 40 and 28 to receive AS 2, 4 and 6 mg/kg/day respectively). Cure rates were high in all treatment groups at 42 days despite almost half the patients remaining parasitemic on Day 3. There was no impact of increasing AS dose on median parasite clearance times, median parasite clearance rates or on the proportion of patients remaining parasitemic on Day 3. However at the lowest dose used (2 mg/kg/d) patients with parasitemia >10,000/µL had longer median (IQR) parasite clearance times than those with parasitemia <10,000/µL (63 (48-75) vs. 84 (66-96) hours, p<0.0001). 19% of patients in the high-dose arm developed neutropenia (absolute neutrophil count <1.0×10(9)/L) by Day 14 and resulted in the arm being halted early. CONCLUSION: There is no pharmacodynamic benefit of increasing the daily dose of AS (4 mg/kg) currently recommended for short-course combination treatment of uncomplicated malaria, even in regions with emerging artemisinin resistance, as long as the partner drug retains high efficacy. TRIAL REGISTRATION: ClinicalTrials.gov NCT00722150.