Regimens are defined using the new_regimen() function. You should provide information on the dose amount, how many doses, and the dosing interval. However, how you provide that information is very flexible. You can e.g. specify:

reg1 <- new_regimen(
  amt = 100,
  interval = 12,
  n = 5
)

which will administer 5 doses of 100 mg (or whatever the unit is), at an interval of 12 hours. The same can however also be specified as:

reg1 <- new_regimen(
  amt = 100,
  times = c(0, 12, 24, 36, 48)
)

or:

reg1 <- new_regimen(
  amt = c(100, 100, 100, 100, 100),
  times = c(0, 12, 24, 36, 48)
)

Be careful: if the length of the amt vector is not the same as the length in times, the function will repeat the first amt specified. The same goes for the arguments type, cmt, and t_inf.

By default, the new_regimen() function assumes the dose is given as bolus. If you want to specify that these should be given as infusion, specify the type and t_inf arguments:

reg1 <- new_regimen(
  amt = 100,
  times = c(0, 12, 24, 36, 48),
  type = "infusion",
  t_inf = c(1, 1, 1.5, 1.5, 1)
)

When you created the model using new_ode_model, you also specified a default dosing compartment. If you didn’t specify the dose argument, the default dosing compartment is 1. Now, should you want to administer the dose into a different compartment, you can override it with the cmt argument:

reg1 <- new_regimen(
  amt = 100,
  times = c(0, 12, 24, 36, 48),
  cmt = c(1, 1, 2, 2, 3)
)

Which will administer the doses to compartments 1, 1, 2, 2, and 3, respectively (of course this is a hypothetical example).

Note: PKPDsim doesn’t care about what unit the dose is in, you have to define this yourself in conjunction with the model code and observation scale.

Steady state

Instead of simulating the full concentration time course for a given model, if you want to simulate the PK(PD) at steady state, you can also specify the ss = TRUE argument to new_regimen(), which will then simulate the regimen at steady state. By default, steady state is assumed to occur after 5 days (PKPDsim doesn’t check if steady state is reached!), but if you want to decrease or increase this you can do so by specifying the n_ss argument, which takes the number of doses to simulate before assuming steady state.

reg_ss <- new_regimen(
  amt = 100,
  interval = 12,
  n = 5,
  ss = TRUE,
  n_ss = 10
)
reg_ss

## Note: Steady state regimen, steady state assumed to be reached at t = 0.

##    t  type amt t_inf
## 1  0 bolus 100     0
## 2 12 bolus 100     0
## 3 24 bolus 100     0
## 4 36 bolus 100     0
## 5 48 bolus 100     0

- Steady state