title: Effect of high-dose vitamin C on the steady-state pharmacokinetics of the protease inhibitor indinavir in healthy volunteers.
abstract: OBJECTIVE
  To determine whether daily high-dose vitamin C alters the steady-state pharmacokinetics of indinavir, a protease inhibitor indicated for treatment of the human immunodeficiency virus type 1.
  
  
  METHODS
  Prospective, open-label, longitudinal, two-period time series.
  
  
  METHODS
  University medical center.
  
  
  METHODS
  Seven healthy volunteers.
  
  
  METHODS
  Indinavir 800 mg every 8 hours was given to subjects for four doses on days 1 and 2. Plasma samples were then collected for indinavir pharmacokinetic determination. After a 7-day washout period, subjects were given vitamin C 1000 mg/day for 7 days. Beginning on day 6 of vitamin C administration, indinavir 800 mg every 8 hours was restarted for four doses. Plasma was then collected from subjects to determine indinavir pharmacokinetics. All subjects were given a vitamin C content-controlled diet for 1 week before the study began and throughout the study period.
  
  
  RESULTS
  Steady-state plasma samples were collected before dosing (0 hr) and 0.5, 1, 2, 3, 4, and 5 hours after dosing to determine indinavir pharmacokinetics. Parameters of interest were maximum plasma concentration (C max ), time to C max , area under the plasma concentration-time curve from 0-5 hours after the dose (AUC 0-5 ), an extrapolated 8-hour AUC (AUC 0-8 ), trough (minimum) plasma concentration (C min ), and oral clearance. Mean steady-state indinavir C max was significantly reduced (20%) after 7 days of vitamin C administration (10.3 +/- 1.5 vs 8.2 +/- 2.9 microg/ml, p=0.04). The corresponding mean AUC 0-8 was also significantly decreased (14%; 26.4 +/- 7.2 vs 22.7 +/- 8.1 microg*hr/ml, p=0.05). Although not statistically significant, the mean indinavir C min was 32% lower in the presence of vitamin C (0.27 +/- 0.17 C vs 0.18 +/- 0.08 microg/ml, p=0.09). Indinavir oral clearance and half-life were not significantly different.
  
  
  CONCLUSIONS
  Concomitant administration of high doses of vitamin C can reduce steady-state indinavir plasma concentrations. Subtherapeutic concentrations of antiretroviral agents have been associated with viral resistance and regimen failure, but the clinical significance of our findings remains to be established.
authors.affiliation: School of Pharmacy, West Virginia University, Morgantown, West Virginia 26506-9520, USA. dslain@hsc.wvu.edu
authors.forename: Douglas
authors.initials: D
authors.lastname: Slain
authors.forename: Jarrett R
authors.initials: JR
authors.lastname: Amsden
authors.forename: Rashida A
authors.initials: RA
authors.lastname: Khakoo
authors.forename: Melanie A
authors.initials: MA
authors.lastname: Fisher
authors.forename: David
authors.initials: D
authors.lastname: Lalka
authors.forename: Gerry R
authors.initials: GR
authors.lastname: Hobbs
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000975:Antioxidants / Q000008:administration & dosage / Q000494:pharmacology*; D019540:Area Under Curve; D001205:Ascorbic Acid / Q000008:administration & dosage / Q000494:pharmacology*; D004347:Drug Interactions; D005260:Female; D017320:HIV Protease Inhibitors / Q000097:blood / Q000493:pharmacokinetics*; D006207:Half-Life; D006801:Humans; D019469:Indinavir / Q000097:blood / Q000493:pharmacokinetics*; D008297:Male; D008657:Metabolic Clearance Rate
chemical_list: D000975:Antioxidants; D017320:HIV Protease Inhibitors; D019469:Indinavir; D001205:Ascorbic Acid