Structural model - IV infusion - Two compartment Model

Route of administration - Rapid intravenous infusion of recombinant human superoxide dismutase (r-hSOD)

Dosage Regimen - 20mg/kg IV rapid infusion for 15 seconds in two categories of rats

Number of Subjects - 1 normal rat, 1 clamped (nephrectomized) rat

In this model, collection of plasma concentration data of parent drug and concentration of parent and metabolite in urine, will help you to derive/ the parameters: Clearance, Volume of Distribution, Km, Vmax.

To note that clearance and volume of central compartment are reduced in clamped rats, as removal of the kidneys increased the effective half life from 10mins in normal rats to 90mins in nephrectomized rats.

The time to steady state might differ 9-fold between the two groups.

Importance of kidneys in the elimination of r-hSOD and the impact of kidney disease/nephrectomy in the overall kinetics of the drug.

In this tutorial, you will learn how to construct a simple two compartment model with 2 set of parameters corresponding to normal and clamped rats.

Call the "necessary" libraries to get started

using Random using Pumas using PumasUtilities using CairoMakie

pk_52 = @model begin @metadata begin desc = "Two Compartment Model" timeu = u"minute" end @param begin "Clearance (mL/min/kg)" tvcl ∈ RealDomain(lower=0) "Volume of Central Compartment (ml/min/kg)" tvvc ∈ RealDomain(lower=0) "Volume of Peripheral Compartment (ml/min/kg)" tvvp ∈ RealDomain(lower=0) "Intercompartmental Clearance (ml/min/kg)" tvcld ∈ RealDomain(lower=0) Ω ∈ PDiagDomain(4) σ²_prop ∈ RealDomain(lower=0) end @random begin η ~ MvNormal(Ω) end @pre begin Cl = tvcl * exp(η[1]) Vc = tvvc * exp(η[2]) Vp = tvvp * exp(η[3]) Cld = tvcld * exp(η[4]) end @dynamics begin Central' = -(Cl/Vc)*Central - (Cld/Vc)*Central + (Cld/Vp) * Peripheral Peripheral' = (Cld/Vc)*Central - (Cld/Vp)*Peripheral end @derived begin cp = @. Central/Vc """ Observed Concentration (ug/mL) """ dv ~ @. Normal(cp,sqrt(cp^2*σ²_prop)) end end

PumasModel Parameters: tvcl, tvvc, tvvp, tvcld, Ω, σ²_prop Random effects: η Covariates: Dynamical variables: Central, Peripheral Derived: cp, dv Observed: cp, dv

Parameters are provided for the simulation as below. `tv`

represents the typical value for parameters.

$tvcl$ - Clearance (mL/min/kg)

$tvvc$ - Volume of Central Compartment (ml/min/kg)

$tvvp$ - Volume of Peripheral CompartmentRenal (ml/min/kg)

$tq$ - Intercompartmental Clearance (ml/min/kg)

$Ω$ - Between Subject Variability

$σ$ - Residual errors

param1 = (tvcl = 3.0, tvvc = 31, tvvp = 15, tvcld = 0.12, Ω = Diagonal([0.0,0.0,0.0,0.0]), σ²_prop = 0.04) param2 = (tvcl = 0.22, tvvc = 16, tvvp = 13, tvcld = 0.09, Ω = Diagonal([0.0,0.0,0.0,0.0]), σ²_prop = 0.04) param = vcat(param1, param2)

A dose of **20 mg/kg** to a single rat of `2 categories`

(normal and clamped)

ev1 = DosageRegimen(20000, cmt = 1) sub1 = Subject(id = "Normal_Rat", events = ev1, covariates = (Rat = "Normal_Rat",)) sub2 = Subject(id = "Clamped_Rat", events = ev1, covariates = (Rat = "Clamped_Rat",)) pop2_sub = [sub1,sub2]

Population Subjects: 2 Covariates: Rat Observations:

Simulate the plasma concentration after IV infusion

Random.seed!(123) sim_pop2_sub = map(((subject, param),) -> simobs(pk_52, subject, param, obstimes=0:0.1:500), zip(pop2_sub, param))

f, a, p = sim_plot(pk_52, sim_pop2_sub, observations = :cp, color = :redsblues, linewidth = 4, axis = (xlabel = "Time (hrs)", ylabel = "PK52 Concentrations (μg/L)", xticks = 0:50:500, yscale = log10, title="Simulated impact of disease on r-hSOD kinetics")) axislegend(a) f