One-Compartment Oral (Warfarin)

This example fits a one-compartment oral pharmacokinetic model to warfarin concentration data.

Model File (warfarin.ferx)

# One-compartment oral PK model (warfarin)

[parameters]
  theta TVCL(0.2, 0.001, 10.0)
  theta TVV(10.0, 0.1, 500.0)
  theta TVKA(1.5, 0.01, 50.0)

  omega ETA_CL ~ 0.09
  omega ETA_V  ~ 0.04
  omega ETA_KA ~ 0.30

  sigma PROP_ERR ~ 0.02

[individual_parameters]
  CL = TVCL * exp(ETA_CL)
  V  = TVV  * exp(ETA_V)
  KA = TVKA * exp(ETA_KA)

[structural_model]
  pk one_cpt_oral(cl=CL, v=V, ka=KA)

[error_model]
  DV ~ proportional(PROP_ERR)

[fit_options]
  method     = foce
  maxiter    = 300
  covariance = true

Model Description

• Structure: One-compartment model with first-order absorption (KA) and first-order elimination (CL/V)
• Random effects: Log-normal on CL, V, and KA (exponential eta model)
• Error model: Proportional residual error
• Parameters:
  • TVCL: Typical value of clearance (L/h)
  • TVV: Typical value of volume of distribution (L)
  • TVKA: Typical value of absorption rate constant (1/h)

Running

ferx examples/warfarin.ferx --data data/warfarin.csv

Expected Results

--- THETA Estimates ---
TVCL                 0.132735
TVV                  7.694842
TVKA                 0.757498

--- OMEGA Estimates (variances) ---
OMEGA(1,1) = 0.028584  (CV% = 16.9)
OMEGA(2,2) = 0.009613  (CV% = 9.8)
OMEGA(3,3) = 0.340868  (CV% = 58.4)

--- SIGMA Estimates ---
SIGMA(1) = 0.010638

SAEM Variant

The same model can be run with SAEM by changing the [fit_options]:

[fit_options]
  method        = saem
  n_exploration = 150
  n_convergence = 250
  n_mh_steps    = 3
  seed          = 12345
  covariance    = true

ferx examples/warfarin_saem.ferx --data data/warfarin.csv