title: Analysis of combination drug therapy to develop regimens with shortened duration of treatment for tuberculosis.
abstract: BACKGROUND
  Tuberculosis remains a worldwide problem, particularly with the advent of multi-drug resistance. Shortening therapy duration for Mycobacterium tuberculosis is a major goal, requiring generation of optimal kill rate and resistance-suppression. Combination therapy is required to attain the goal of shorter therapy.
  
  
  OBJECTIVE
  Our objective was to identify a method for identifying optimal combination chemotherapy. We developed a mathematical model for attaining this end. This is accomplished by identifying drug effect interaction (synergy, additivity, antagonism) for susceptible organisms and subpopulations resistant to each drug in the combination.
  
  
  METHODS
  We studied the combination of linezolid plus rifampin in our hollow fiber infection model. We generated a fully parametric drug effect interaction mathematical model. The results were subjected to Monte Carlo simulation to extend the findings to a population of patients by accounting for between-patient variability in drug pharmacokinetics.
  
  
  RESULTS
  All monotherapy allowed emergence of resistance over the first two weeks of the experiment. In combination, the interaction was additive for each population (susceptible and resistant). For a 600 mg/600 mg daily regimen of linezolid plus rifampin, we demonstrated that >50% of simulated subjects had eradicated the susceptible population by day 27 with the remaining organisms resistant to one or the other drug. Only 4% of patients had complete organism eradication by experiment end.
  
  
  CONCLUSIONS
  These data strongly suggest that in order to achieve the goal of shortening therapy, the original regimen may need to be changed at one month to a regimen of two completely new agents with resistance mechanisms independent of the initial regimen. This hypothesis which arose from the analysis is immediately testable in a clinical trial.
authors.affiliation: Institute for Therapeutic Innovation, College of Medicine, University of Florida, Lake Nona, Florida, United States of America.
authors.forename: George L
authors.initials: GL
authors.lastname: Drusano
authors.affiliation: Laboratory of Applied Pharmacokinetics, School of Medicine, University of Southern California, Los Angeles, California, United States of America.
authors.forename: Michael
authors.initials: M
authors.lastname: Neely
authors.affiliation: Laboratory of Applied Pharmacokinetics, School of Medicine, University of Southern California, Los Angeles, California, United States of America.
authors.forename: Michael
authors.initials: M
authors.lastname: Van Guilder
authors.affiliation: Laboratory of Applied Pharmacokinetics, School of Medicine, University of Southern California, Los Angeles, California, United States of America.
authors.forename: Alan
authors.initials: A
authors.lastname: Schumitzky
authors.affiliation: Institute for Therapeutic Innovation, College of Medicine, University of Florida, Lake Nona, Florida, United States of America.
authors.forename: David
authors.initials: D
authors.lastname: Brown
authors.affiliation: Institute for Therapeutic Innovation, College of Medicine, University of Florida, Lake Nona, Florida, United States of America.
authors.forename: Steven
authors.initials: S
authors.lastname: Fikes
authors.affiliation: Infectious Diseases PK Laboratory, College of Pharmacy, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Charles
authors.initials: C
authors.lastname: Peloquin
authors.affiliation: Institute for Therapeutic Innovation, College of Medicine, University of Florida, Lake Nona, Florida, United States of America.
authors.forename: Arnold
authors.initials: A
authors.lastname: Louie
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D003198:Computer Simulation; D004347:Drug Interactions; D004359:Drug Therapy, Combination; D000069349:Linezolid / Q000494:pharmacology*; D008962:Models, Theoretical; D009010:Monte Carlo Method; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D012293:Rifampin / Q000494:pharmacology*; D013997:Time Factors; D014376:Tuberculosis / Q000188:drug therapy* / Q000382:microbiology
chemical_list: D000995:Antitubercular Agents; D000069349:Linezolid; D012293:Rifampin