title: Development of a dosage strategy in patients receiving enoxaparin by continuous intravenous infusion using modelling and simulation.
abstract: OBJECTIVE
  To develop an appropriate dosing strategy for continuous intravenous infusions (CII) of enoxaparin by minimizing the percentage of steady-state anti-Xa concentration (C(ss)) outside the therapeutic range of 0.5-1.2 IU ml(-1).
  
  
  METHODS
  A nonlinear mixed effects model was developed with NONMEM for 48 adult patients who received CII of enoxaparin with infusion durations that ranged from 8 to 894 h at rates between 100 and 1600 IU h(-1). Three hundred and sixty-three anti-Xa concentration measurements were available from patients who received CII. These were combined with 309 anti-Xa concentrations from 35 patients who received subcutaneous enoxaparin. The effects of age, body size, height, sex, creatinine clearance (CrCL) and patient location [intensive care unit (ICU) or general medical unit] on pharmacokinetic (PK) parameters were evaluated. Monte Carlo simulations were used to (i) evaluate covariate effects on C(ss) and (ii) compare the impact of different infusion rates on predicted C(ss). The best dose was selected based on the highest probability that the C(ss) achieved would lie within the therapeutic range.
  
  
  RESULTS
  A two-compartment linear model with additive and proportional residual error for general medical unit patients and only a proportional error for patients in ICU provided the best description of the data. Both CrCL and weight were found to affect significantly clearance and volume of distribution of the central compartment, respectively. Simulations suggested that the best doses for patients in the ICU setting were 50 IU kg(-1) per 12 h (4.2 IU kg(-1) h(-1)) if CrCL < 30 ml min(-1); 60 IU kg(-1) per 12 h (5.0 IU kg(-1) h(-1)) if CrCL was 30-50 ml min(-1); and 70 IU kg(-1) per 12 h (5.8 IU kg(-1) h(-1)) if CrCL > 50 ml min(-1). The best doses for patients in the general medical unit were 60 IU kg(-1) per 12 h (5.0 IU kg(-1) h(-1)) if CrCL < 30 ml min(-1); 70 IU kg(-1) per 12 h (5.8 IU kg(-1) h(-1)) if CrCL was 30-50 ml min(-1); and 100 IU kg(-1) per 12 h (8.3 IU kg(-1) h(-1)) if CrCL > 50 ml min(-1). These best doses were selected based on providing the lowest equal probability of either being above or below the therapeutic range and the highest probability that the C(ss) achieved would lie within the therapeutic range.
  
  
  CONCLUSIONS
  The dose of enoxaparin should be individualized to the patients' renal function and weight. There is some evidence to support slightly lower doses of CII enoxaparin in patients in the ICU setting.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, PA 15261, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Feng
authors.forename: Bruce
authors.initials: B
authors.lastname: Green
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Duffull
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Kane-Gill
authors.forename: Mary B
authors.initials: MB
authors.lastname: Bobek
authors.forename: Robert R
authors.initials: RR
authors.lastname: Bies
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage* / Q000493:pharmacokinetics; D001835:Body Weight / Q000502:physiology; D003404:Creatinine / Q000378:metabolism; D003422:Critical Care / Q000379:methods; D004334:Drug Administration Schedule; D017984:Enoxaparin / Q000008:administration & dosage* / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D007668:Kidney / Q000503:physiopathology; D016014:Linear Models; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D012189:Retrospective Studies; D013923:Thromboembolism / Q000188:drug therapy / Q000503:physiopathology; D020246:Venous Thrombosis / Q000188:drug therapy / Q000503:physiopathology
chemical_list: D000925:Anticoagulants; D017984:Enoxaparin; D003404:Creatinine