title: A semimechanistic-physiologic population pharmacokinetic/pharmacodynamic model for neutropenia following pemetrexed therapy.
abstract: OBJECTIVE
  The objectives of these analyses were to (1) develop a semimechanistic-physiologic population pharmacokinetic/pharmacodynamic (PK/PD) model to describe neutropenic response to pemetrexed and to (2) identify influential covariates with respect to pharmacodynamic response.
  
  
  METHODS
  Data from 279 patients who received 1,136 treatment cycles without folic acid or vitamin B12 supplementation during participation in one of eight phase II cancer trials were available for analysis. Starting doses were 500 or 600 mg pemetrexed per m2 body surface area (BSA), administered as 10-min intravenous infusions every 21 days (1 cycle). The primary analyses included 105 patients (279 cycles) for which selected covariates-including vitamin deficiency marker data (i.e., homocysteine, cystathionine, methylmalonic acid, and methylcitrate [I, II, and total] plasma concentrations)-were available. Classical statistical multivariate regression analyses and a semimechanistic-physiologic population PK/PD model were used to evaluate neutropenic response to single-agent pemetrexed administration.
  
  
  RESULTS
  The timecourse of neutropenia following single-agent pemetrexed administration was adequately described by a semimechanistic-physiologic model. Population estimates for system-based model parameters (i.e., baseline neutrophil count, mean transit time, and the feedback parameter), which mathematically represent current understanding of the process and physiology of hematopoiesis, were consistent with previously reported values. The population PK/PD model included homocysteine, cystathionine, albumin, total protein, and BSA as covariates relative to neutropenic response.
  
  
  CONCLUSIONS
  These results support the programmatic decision to introduce folic acid and vitamin B12 supplementation during pemetrexed clinical development as a means of normalizing patient homocysteine levels, thereby managing the risk of severe neutropenia secondary to pemetrexed administration. The current results also suggest that the addition of vitamin B6 supplementation to normalize patient cystathionine levels may further decrease the incidence of grade 4 neutropenia following pemetrexed administration. The results also suggest the use of folic acid as a means of lessening hematologic toxicity following administration of cytotoxic agents other than antifolates.
authors.affiliation: Global Pharmacokinetics, Pharmacodynamics, and Trial Simulation, Lilly Research Laboratories, Lilly Corporate Center, Eli Lilly and Company, Indianapolis, IN 46285, USA. latz_jane_e@lilly.com
authors.forename: Jane E
authors.initials: JE
authors.lastname: Latz
authors.forename: Mats O
authors.initials: MO
authors.lastname: Karlsson
authors.forename: James J
authors.initials: JJ
authors.lastname: Rusthoven
authors.forename: Atalanta
authors.initials: A
authors.lastname: Ghosh
authors.forename: Robert D
authors.initials: RD
authors.lastname: Johnson
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D000704:Analysis of Variance; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics*; D019540:Area Under Curve; D001361:Avitaminosis / Q000378:metabolism; D001772:Blood Cell Count; D001830:Body Surface Area; D017322:Clinical Trials, Phase II as Topic; D003627:Data Interpretation, Statistical; D005260:Female; D005492:Folic Acid / Q000627:therapeutic use; D005971:Glutamates / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics*; D006147:Guanine / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D006801:Humans; D007262:Infusions, Intravenous; D007958:Leukocyte Count; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009503:Neutropenia / Q000139:chemically induced* / Q000453:epidemiology / Q000517:prevention & control; D009504:Neutrophils / Q000502:physiology; D000068437:Pemetrexed; D011153:Population; D014805:Vitamin B 12 / Q000627:therapeutic use; D025101:Vitamin B 6 / Q000627:therapeutic use; D014815:Vitamins / Q000627:therapeutic use
chemical_list: D000964:Antimetabolites, Antineoplastic; D005971:Glutamates; D014815:Vitamins; D000068437:Pemetrexed; D006147:Guanine; D025101:Vitamin B 6; D005492:Folic Acid; D014805:Vitamin B 12