bOnly anecdotal data are available on the pharmacokinetics (PK) of miltefosine in children suffering from visceral leishmaniasis (VL). While failure rates were higher in children with VL, steady-state concentrations appeared lower than those seen with adults. We hypothesized that the current linear dosage (in milligrams per kilogram of body weight) is too low for children and that a new dosing algorithm based on an appropriate body size model would result in an optimal exposure. A population PK analysis was performed on three historic pooled data sets, including Indian children, Indian adults, and European adults. Linear and allometric scaling of PK parameters by either body weight or fat-free mass (FFM) was evaluated for body size models. Based on the developed PK model, a dosing algorithm for miltefosine in children and adults was proposed and evaluated in silico. The population PK model employing allometric scaling fitted best to the pooled miltefosine data. Allometric scaling by FFM reduced between-subject variability, e.g., for drug clearance, from 49.6% to 32.1%. A new allometric miltefosine dosing algorithm was proposed. Exposure to miltefosine was lower in children than adults receiving 2.5 mg/kg/day: a C max of 18.8 g/ml was reached by 90% of adults and 66.7% of children. The allometric daily dose resulted in similar levels of exposure to miltefosine for adults and children. The use of a new allometric dosing algorithm for miltefosine in VL patients results in optimal exposure to miltefosine in both adults and children and might improve clinical outcome in children.V isceral leishmaniasis (VL) or kala-azar (Hindi for "black fever") has been classified as one of the world's "most neglected diseases" (62), and of all the parasitic diseases, it ranks third in terms of morbidity and mortality after only malaria and lymphatic filariasis (38). The World Health Organization (WHO) reported in 2004 that leishmaniasis is responsible for around 50,000 deaths and almost 2 million disability-adjusted life-years per year, approximately half of which can be attributed to children from lowincome countries (38, 60), but in reality the burden of leishmaniasis is probably much larger due to massive underreporting of both cases and deaths in the often remote areas where leishmaniasis is prevalent (47).Miltefosine (hexadecylphosphocholine; marketed by Paladin Laboratories Inc. as Impavido) is the newest addition to the small repertory of antileishmanial drugs and to date is the only drug that can be administered orally. It has achieved relatively high cure rates in the treatment of visceral (8, 26, 41, 52, 54), New World cutaneous (11,44,48,50,57), Old World cutaneous (30, 56) and even difficult-to-treat mucocutaneous (49, 51) leishmaniasis.During the development of miltefosine, two clinical trials were designed to investigate the efficacy and safety of miltefosine in children (Ͻ12 years of age) in which a total of 119 pediatric patients were enrolled, employing dosages linearly extrapolated from the daily adult dosage (in ...