ORIGINAL PAPER Mass balance and metabolism of the antimalarial pyronaridine in healthy volunteers Carrie A. Morris • Stephen R. Dueker • Peter N. Lohstroh • Li-Quan Wang • Xin-Ping Fang • Donald Jung • Luis Lopez-Lazaro • Mark Baker • Stephan Duparc • Isabelle Borghini-Fuhrer • Rolf Pokorny • Jang-Sik Shin • Lawrence Fleckenstein Received: 4 July 2013 / Accepted: 21 February 2014 Ó Springer International Publishing Switzerland 2014 Abstract This was a single dose mass balance and metabolite characterization study of the antimalarial agent pyronaridine. Six healthy male adults were administered a single oral dose of 720 mg pyronaridine tetraphosphate with 800 nCi of radiolabeled 14 C-pyronaridine. Urine and feces were continuously collected through 168 h post-dose, with intermittent 48 h collection periods thereafter through 2064 h post-dose. Drug recovery was computed for ana- lyzed samples and interpolated for intervening time periods in which collection did not occur. Blood samples were obtained to evaluate the pharmacokinetics of total radio- activity and of the parent compound. Total radioactivity in urine, feces, and blood samples was determined by accel- erator mass spectrometry (AMS); parent concentrations in blood were determined with LC/MS. Metabolite identifi- cation based on blood, urine, and feces samples was conducted using a combination of LC ? AMS for identi- fying radiopeaks, followed by LC/MS/MS for identity confirmation/elucidation. The mean cumulative drug recovery in the urine and feces was 23.7 and 47.8 %, respectively, with an average total recovery of 71.5 %. Total radioactivity was slowly eliminated from blood, with a mean half-life of 33.5 days, substantially longer than the mean parent compound half-life of 5.03 days. Total radioactivity remained detectable in urine and feces col- lected in the final sampling period, suggesting ongoing elimination. Nine primary and four secondary metabolites of pyronaridine were identified. This study revealed that pyronaridine and its metabolites are eliminated by both the urinary and fecal routes over an extended period of time, and that multiple, varied pathways characterize pyronari- dine metabolism. Keywords Pyronaridine  Mass balance  Metabolism  Antimalarial 1 Introduction Pyronaridine is a benzonaphthyridine derivative antima- larial agent which has demonstrated efficacy against para- site strains resistant to other antimalarials, including amodiaquine and chloroquine (Croft et al. 2012). Pyro- naridine tetraphosphate has been co-formulated in a 3:1 ratio with the artemisinin derivative artesunate to yield an oral artesmisinin based combination therapy indicated for the treatment of acute uncomplicated falciparum and vivax malaria in children and adults. Pyronaridine is a highly lipophilic compound which displays extensive distribution and slow in vivo elimination, with a typical half-life of 13.2 days in adults with malaria and 11.3 days in healthy C. A. Morris  L. Fleckenstein (&) College of Pharmacy, University of Iowa, Iowa City, IA, USA e-mail: l-fleckenstein@uiowa.edu S. R. Dueker  P. N. Lohstroh Eckert and Ziegler Vitalea Science, Davis, CA, USA L.-Q. Wang  X.-P. Fang XenoBiotic Laboratories, Inc., Plainsboro, NJ, USA D. Jung Pharmaceutical Research Services, Cupertino, CA, USA L. Lopez-Lazaro  R. Pokorny Covance Basel Research Unit AG, Allschwil, Switzerland M. Baker  S. Duparc  I. Borghini-Fuhrer Medicines for Malaria Venture, Geneva, Switzerland J.-S. Shin Shin Poong Pharmaceuticals, Seoul, Republic of Korea Eur J Drug Metab Pharmacokinet DOI 10.1007/s13318-014-0182-0