using Random using Pumas using PumasUtilities

In this tutorial, we will cover the fundamentals of generating populations to simulate with Pumas. We will demonstrate how to specify dosage regimens and covariates, and then how to piece these together to form a population to simulate.

Below is a Pumas model that specifies a 1-compartment oral absorption system with between-subject variability on all the parameters. Details of the model specification are provided in the documentation.

model = @model begin @param begin θ ∈ VectorDomain(4) Ω ∈ PSDDomain(3) σ²_prop ∈ RealDomain(init=0.1) end @random begin η ~ MvNormal(Ω) end @covariates Wt @pre begin CL = θ[1]*(Wt/70)^0.75*exp(η[1]) V = θ[2]*(Wt/70)^0.75*exp(η[2]) Ka = θ[3]*exp(η[3]) end @dynamics begin Depot' = -Ka*Depot Central' = Ka*Depot - Central*CL/V end @derived begin conc = @. Central/V dv ~ @.Normal(conc,sqrt(conc^2*σ²_prop)) end end

PumasModel Parameters: θ, Ω, σ²_prop Random effects: η Covariates: Wt Dynamical variables: Depot, Central Derived: conc, dv Observed: conc, dv

Next we provide the initial estimates of the parameters to simulate from. The fixed effects are provided in the θ vector (CL, V, Ka) and the between-subject variability parameteres are provided in the Ω vector as variances. So, 0.04 variance on Ω*11 suggests a 20% coefficient of variation. Similarly, σ²*prop has a 20% proportional residual error.

fixeffs = ( θ = [0.4,20,1.1,2], Ω = diagm(0 => [0.04,0.04,0.04]), σ²_prop = 0.04 )

(θ = [0.4, 20.0, 1.1, 2.0], Ω = [0.04 0.0 0.0; 0.0 0.04 0.0; 0.0 0.0 0.04], σ²_prop = 0.04)

`DosageRegimen()`

is the function that lets you construct a dosing regimen. The first argument of the `DosageRegimen`

is `amt`

and is not a named argument. All subsequent arguments need to be named. Lets try a simple example where you provide a 100 mg dose at `time = 0`

.

ev = DosageRegimen(100, time = 0) first(ev.data)

DataFrameRow (10 columns)

time | cmt | amt | evid | ii | addl | rate | duration | ss | route | |
---|---|---|---|---|---|---|---|---|---|---|

Float64 | Int64 | Float64 | Int8 | Float64 | Int64 | Float64 | Float64 | Int8 | Route… | |

1 | 0.0 | 1 | 100.0 | 1 | 0.0 | 0 | 0.0 | 0.0 | 0 | NullRoute |

As you can see above, we provided a single 100 mg dose. `DosageRegimen`

provides some defaults when it creates the dataset, `time = 0`

, `evid = 1`

, `cmt = 1`

, `rate = 0`

, `ii = 0`

& `addl = 0`

.

Note that `ev`

is of type `DosageRegimen`

. Specified like above, `DosageRegimen`

is one of the four fundamental building block of a `Subject`

(more on `Subject`

below).

Let's create a single subject

s1 = Subject(id = 1, events = ev, covariates = (Wt = 70,), observations = (dv = nothing,))

Subject ID: 1 Events: 1 Observations: dv: (nothing) Covariates: Wt

Note that the `s1`

`Subject`

created above is composed of:

`id`

: an unique identifier`observations`

: observations, represented by`Pumas.Observation`

`covariates`

: covariates, represented by`Pumas.ConstantCovar`

`events`

: events, represented by`Pumas.Event`

DataFrame(s1.events)

1 rows × 11 columns (omitted printing of 1 columns)

amt | time | evid | cmt | rate | duration | ss | ii | base_time | rate_dir | |
---|---|---|---|---|---|---|---|---|---|---|

Float64 | Float64 | Int8 | Int64 | Float64 | Float64 | Int8 | Float64 | Float64 | Int8 | |

1 | 100.0 | 0.0 | 1 | 1 | 0.0 | Inf | 0 | 0.0 | 0.0 | 1 |

The events are presented by basic information such as the dose of drug, the time of dose administration, the compartment number for administration and whether the dose is an instantaneous input or an infusion.

Below is how the covariates are represented, as a `NamedTuple`

.

s1.covariates

Pumas.ConstantCovar{NamedTuple{(:Wt,), Tuple{Int64}}}((Wt = 70,))

(Note: defining distributions for covariates will be discussed in detail later.)

Using this one subject, `s1`

, let us simulate a simple concentration time profile using the model above:

Random.seed!(1234) sims = simobs(model, s1, fixeffs, obstimes = 0:0.1:120)

and plot the result

sim_plot(model, [sims], observations = [:conc], figure = (fontsize = 18, ), axis = (xlabel = "Time (hr)", ylabel = "Predicted Concentration (ng/mL)"))

Now, lets create one more subject, `s2`

.

s2 = Subject(id = 2, events = ev, covariates = (Wt = 70,), observations = (dv = nothing,))

Subject ID: 2 Events: 1 Observations: dv: (nothing) Covariates: Wt

If we want to simulate both `s1`

and `s2`

together, we need to bring these subjects together to form a `Population`

. A `Population`

is essentially a collection of subjects.

twosubjs = [s1,s2]

Population Subjects: 2 Covariates: Wt Observations: dv

Let's see the details of the first and the second subject

twosubjs[1]

Subject ID: 1 Events: 1 Observations: dv: (nothing) Covariates: Wt

twosubjs[2]

Subject ID: 2 Events: 1 Observations: dv: (nothing) Covariates: Wt

Now, we can simulate this `Population`

of 2 subjects as below

Random.seed!(1234) sims = simobs(model, twosubjs, fixeffs, obstimes = 0:0.1:120)

and plot the result

sim_plot(model, sims, observations = [:conc], figure = (fontsize = 18, ), axis = (xlabel = "Time (hr)", ylabel = "Predicted Concentration (ng/mL)"))

Similarly, we can build a population of any number of subjects. But before we do that, let's dive into covariate generation.

As was discussed earlier, a `Subject`

can also be provided details regarding covariates. In the model above, a continuous covariate body weight `Wt`

impacts both `CL`

and `V`

. Let us now specify covariates to a population of 10 subjects.

Random.seed!(1234) choose_covariates() = (Wt = rand(55:80),)

choose_covariates (generic function with 1 method)

`choose_covariates`

will randomly choose a `Wt`

between 55-80 kgs

We can make a list with covariates for ten subjects through a list comprehension

cvs = [ choose_covariates() for i in 1:10 ] DataFrame(cvs)

10 rows × 1 columns

Wt | |
---|---|

Int64 | |

1 | 67 |

2 | 70 |

3 | 79 |

4 | 70 |

5 | 58 |

6 | 66 |

7 | 78 |

8 | 58 |

9 | 58 |

10 | 73 |

Now, we add these covariates to the population as below. The `map(f,xs)`

will return the result of `f`

on each element of `xs`

. Let's map a function that build's a subject with the randomly chosen covariates in order to build a population:

pop_with_covariates = map(i -> Subject(id = i, events = ev, covariates = choose_covariates(), observations = (dv = nothing,)), 1:10)

Population Subjects: 10 Covariates: Wt Observations: dv

Simulate into the population

Random.seed!(1234) sims = simobs(model, pop_with_covariates, fixeffs, obstimes = 0:0.1:120)

and visualize the output

sim_plot(model, sims, observations = [:conc], figure = (fontsize = 18, ), axis = (xlabel = "Time (hr)", ylabel = "Predicted Concentration (ng/mL)"))

`DosageRegimen`

provides additional controls over the specification of the regimen. For example, `ii`

defines the "interdose interval", or the time difference between two doses, while `addl`

defines how many additional times to repeat a dose. Thus, let's define a dose of 100 that's repeated 7 times at 24 hour intervals:

md = DosageRegimen(100, ii = 24, addl = 6)

1 rows × 10 columns

time | cmt | amt | evid | ii | addl | rate | duration | ss | route | |
---|---|---|---|---|---|---|---|---|---|---|

Float64 | Int64 | Float64 | Int8 | Float64 | Int64 | Float64 | Float64 | Int8 | Route… | |

1 | 0.0 | 1 | 100.0 | 1 | 24.0 | 6 | 0.0 | 0.0 | 0 | NullRoute |

Let's create a new subject, `s3`

with this dosage regimen:

s3 = Subject(id = 3, events = md, covariates = (Wt = 70,), observations = (dv = nothing,))

Subject ID: 3 Events: 7 Observations: dv: (nothing) Covariates: Wt

and see the results:

Random.seed!(1234) sims = simobs(model, s3, fixeffs, obstimes = 0:0.1:240)

sim_plot(model, [sims], observations = [:conc], figure = (fontsize = 18, ), axis = (xlabel = "Time (hr)", ylabel = "Predicted Concentration (ng/mL)"))

We can also combine dosage regimens to build a more complex regimen. Recall from the introduction that using arrays will build the element-wise combinations. Thus let's build a dose of 500 into compartment 1 at time 0, and 7 doses into compartment 1 of 100 spaced by 24 hours:

ldmd = DosageRegimen([500,100], time = [0,24], cmt = 1, addl = [0,6], ii = [0,24])

2 rows × 10 columns

time | cmt | amt | evid | ii | addl | rate | duration | ss | route | |
---|---|---|---|---|---|---|---|---|---|---|

Float64 | Int64 | Float64 | Int8 | Float64 | Int64 | Float64 | Float64 | Int8 | Route… | |

1 | 0.0 | 1 | 500.0 | 1 | 0.0 | 0 | 0.0 | 0.0 | 0 | NullRoute |

2 | 24.0 | 1 | 100.0 | 1 | 24.0 | 6 | 0.0 | 0.0 | 0 | NullRoute |

Let's see if this result matches our intuition:

s4 = Subject(id = 4, events = ldmd, covariates = (Wt = 70,), observations = (dv = nothing,)) Random.seed!(1234) sims = simobs(model, s4, fixeffs, obstimes = 0:0.1:120)

sim_plot(model, [sims], observations = [:conc], figure = (fontsize = 18, ), axis = (xlabel = "Time (hr)", ylabel = "Predicted Concentration (ng/mL)"))

Another way to build complex dosage regiments is to combine previously constructed regimens into a single regimen. For example:

e1 = DosageRegimen(500,cmt = 1, time = 0, addl = 0, ii = 0) e2 = DosageRegimen(100,cmt = 1, time = 24, addl = 6, ii = 24) evs = DosageRegimen(e1,e2) s5 = Subject(id = 5, events = evs, covariates = (Wt = 70,), observations = (dv = nothing,)) Random.seed!(1234) sims = simobs(model, s5, fixeffs, obstimes = 0:0.1:120)

is the same regimen as before.

Putting these ideas together, we can define a population where individuals with different covariates undergo different regimens, and simulate them all together:

e1 = DosageRegimen(100, ii = 24, addl = 6) e2 = DosageRegimen(50, ii = 12, addl = 13) e3 = DosageRegimen(200, ii = 24, addl = 2)

1 rows × 10 columns

time | cmt | amt | evid | ii | addl | rate | duration | ss | route | |
---|---|---|---|---|---|---|---|---|---|---|

Float64 | Int64 | Float64 | Int8 | Float64 | Int64 | Float64 | Float64 | Int8 | Route… | |

1 | 0.0 | 1 | 200.0 | 1 | 24.0 | 2 | 0.0 | 0.0 | 0 | NullRoute |

pop1 = map(i -> Subject(id = i, events = e1, covariates = choose_covariates(), observations = (dv = nothing,)), 1:5) pop2 = map(i -> Subject(id = i, events = e2, covariates = choose_covariates(), observations = (dv = nothing,)), 6:8) pop3 = map(i -> Subject(id = i, events = e3, covariates = choose_covariates(), observations = (dv = nothing,)), 9:10) pop = vcat(pop1, pop2, pop3)

Population Subjects: 10 Covariates: Wt Observations: dv

Random.seed!(1234) sims = simobs(model, pop, fixeffs, obstimes = 0:0.1:120)

sim_plot(model, sims, observations = [:conc], figure = (fontsize = 18, ), axis = (xlabel = "Time (hr)", ylabel = "Predicted Concentration (ng/mL)"))

An infusion is a dosage which is defined as having a non-zero positive rate at which the drug enters the system. Let's define a single infusion dose of total amount 100 with a rate of 3 unit amount per time into the second compartment:

inf = DosageRegimen(100, rate = 3, cmt = 2)

1 rows × 10 columns

time | cmt | amt | evid | ii | addl | rate | duration | ss | route | |
---|---|---|---|---|---|---|---|---|---|---|

Float64 | Int64 | Float64 | Int8 | Float64 | Int64 | Float64 | Float64 | Int8 | Route… | |

1 | 0.0 | 2 | 100.0 | 1 | 0.0 | 0 | 3.0 | 33.3333 | 0 | NullRoute |

Now let's simulate a subject undergoing this treatment strategy:

s6 = Subject(id = 5, events = inf, covariates = (Wt = 70,), observations = (dv = nothing,)) Random.seed!(1234) sims = simobs(model, s6, fixeffs, obstimes = 0:0.1:120)

Note that all of these functions are standard Julia functions, and thus standard Julia programming constructions can be utilized to simplify the construction of large populations. We already demonstrated the use of `map`

and a comprehension, but we can also make use of constructs like `for`

loops.

This tutorial shows the tools for generating populations of infinite complexity, defining covariates and dosage regimens on the fly and simulating the results of the model.