title: Population pharmacokinetics of lopinavir in combination with ritonavir in HIV-1-infected patients.
abstract: OBJECTIVE
  To develop a population pharmacokinetic model for lopinavir in combination with ritonavir, in which the interaction between both drugs was characterized, and in which relationships between patient characteristics and pharmacokinetics were identified.
  
  
  METHODS
  The pharmacokinetics of lopinavir in combination with ritonavir were described using NONMEM (version V, level 1.1). First, ritonavir data were fitted to a previously developed model to obtain individual Bayesian estimates of pharmacokinetic parameters. Hereafter, an integrated model for the description of the pharmacokinetics of lopinavir with ritonavir was designed.
  
  
  RESULTS
  From 122 outpatients 748 lopinavir and 748 ritonavir plasma concentrations were available for analysis. The interaction between the drugs was described by a time-independent inverse relationship between the exposure to ritonavir over a dosing-interval and the apparent clearance (CL/F) of lopinavir. The model parameters volume of distribution and absorption rate constant were 61.6 l (95% prediction interval (PI) 22.4, 83.7) and 0.564 h(-1) (95% PI 0.208, 0.947), respectively. The model yielded a theoretical value for the CL/F of lopinavir without ritonavir of 14.8 l h(-1) (95%PI 12.1, 20.1), which translates to a value of 5.73 l h(-1) in the presence of ritonavir. The only factor with significant effect on the pharmacokinetics was concurrent use of non-nucleoside reverse transcriptase inhibitors (NNRTI), which increased the CL/F of lopinavir by 39% (P < 0.001).
  
  
  CONCLUSIONS
  We have developed a model that has defined a time-independent inverse relationship between the exposure to ritonavir and the CL/F of lopinavir, and provided an adequate description of the pharmacokinetic parameters for the latter. Concomitant use of the NNRTIs efavirenz and nevirapine increased the CL/F of lopinavir.
authors.affiliation: Department of Pharmacy & Pharmacology, Slotervaart Hospital, 1066 EC Amsterdam, the Netherlands. Apkcr@slz.nl
authors.forename: K M L
authors.initials: KM
authors.lastname: Crommentuyn
authors.forename: B S
authors.initials: BS
authors.lastname: Kappelhoff
authors.forename: J W
authors.initials: JW
authors.lastname: Mulder
authors.forename: A T A
authors.initials: AT
authors.lastname: Mairuhu
authors.forename: E C M
authors.initials: EC
authors.lastname: van Gorp
authors.forename: P L
authors.initials: PL
authors.lastname: Meenhorst
authors.forename: A D R
authors.initials: AD
authors.lastname: Huitema
authors.forename: J H
authors.initials: JH
authors.lastname: Beijnen
mesh_terms: D000328:Adult; D019380:Anti-HIV Agents / Q000097:blood / Q000493:pharmacokinetics*; D002214:Capsules; D004338:Drug Combinations; D005260:Female; D015658:HIV Infections / Q000097:blood / Q000188:drug therapy*; D017320:HIV Protease Inhibitors / Q000008:administration & dosage / Q000493:pharmacokinetics*; D015497:HIV-1; D006801:Humans; D061466:Lopinavir; D008297:Male; D008875:Middle Aged; D008956:Models, Chemical; D011744:Pyrimidinones / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D012189:Retrospective Studies; D019438:Ritonavir / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*
chemical_list: D019380:Anti-HIV Agents; D002214:Capsules; D004338:Drug Combinations; D017320:HIV Protease Inhibitors; D011744:Pyrimidinones; D061466:Lopinavir; D019438:Ritonavir