Quick Start

This walkthrough fits a one-compartment oral PK model to warfarin data.

1. Create a model file

Save the following as warfarin.ferx:

[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

2. Prepare your data

Data must be in NONMEM CSV format. The minimum required columns are ID, TIME, and DV. Dosing records use EVID=1 with AMT:

ID,TIME,DV,EVID,AMT,CMT,MDV
1,0,.,1,100,1,1
1,0.5,9.49,0,.,.,0
1,1,14.42,0,.,.,0
1,2,17.56,0,.,.,0
1,4,15.23,0,.,.,0
1,8,10.15,0,.,.,0
1,12,6.75,0,.,.,0
1,24,2.24,0,.,.,0

3. Run the fit

ferx warfarin.ferx --data warfarin.csv

4. Interpret the output

The console output shows the estimation progress and final results:

Starting FOCE estimation...
  10 subjects, 110 observations
  3 thetas, 3 etas, 1 sigmas
...
Final OFV = -280.1838

============================================================
NONLINEAR MIXED EFFECTS MODEL ESTIMATION
============================================================

Converged: YES
Estimation method: FOCE

--- Objective Function ---
OFV:  -280.1838
AIC:  -266.1838
BIC:  -247.2804

--- THETA Estimates ---
Parameter            Estimate           SE       %RSE
----------------------------------------------------
TVCL                 0.132735     0.014549       11.0
TVV                  7.694842     0.293028        3.8
TVKA                 0.757498     0.034986        4.6

--- OMEGA Estimates (variances) ---
  OMEGA(1,1) = 0.028584  (CV% = 16.9)  SE = 0.006394
  OMEGA(2,2) = 0.009613  (CV% = 9.8)   SE = 0.002165
  OMEGA(3,3) = 0.340868  (CV% = 58.4)  SE = 0.076351

--- SIGMA Estimates ---
  SIGMA(1) = 0.010638  SE = 0.000788

5. Output files

Three files are generated:

Next Steps

• Learn the full Model File Reference
• Explore Estimation Methods (FOCE, FOCEI, SAEM)
• See more Examples