Transit Compartment Absorption Model¶

Model with transit compartments for delayed/complex oral absorption.

Model Schematic¶

Oral Dose
    │
    ▼
┌─────────┐  Ktr   ┌─────────┐  Ktr   ┌─────────┐  Ktr   ┌─────────┐  Ka   ┌─────────────┐
│Transit 1│ ────▶ │Transit 2│ ────▶ │Transit 3│ ────▶ │  ... n  │ ────▶│   Central   │
└─────────┘       └─────────┘       └─────────┘       └─────────┘      │      V      │
                                                                        └──────┬──────┘
                                                                               │ CL
                                                                               ▼
                                                                          Elimination

Key Equations¶

The transit model uses n identical transit compartments with rate constant Ktr:

dA₁/dt = -Ktr × A₁
dAᵢ/dt = Ktr × Aᵢ₋₁ - Ktr × Aᵢ   (for i = 2 to n)
dA_central/dt = Ktr × Aₙ - CL/V × A_central

Mean Transit Time (MTT):

MTT = (n + 1) / Ktr

Parameters¶

Parameter	Description	Typical Range	Units
Ktr	Transit rate constant	0.5-5.0	1/h
n	Number of transit compartments	1-10	-
CL	Clearance	1-50	L/h
V	Volume of distribution	10-500	L

Example Values¶

Parameter	Value	Rationale
Ktr	2.0 1/h	MTT ≈ 2h with n=3
n	3	3 transit compartments
CL	5.0 L/h	Moderate clearance
V	50.0 L	Total body water
Dose	100 mg	Oral dose

Key Features¶

Delayed Tmax compared to first-order absorption
Sharper peak than first-order absorption
More physiologically realistic for enteric-coated tablets
Flexible: adjusting n and Ktr can model various profiles

Use Cases¶

Enteric-coated formulations
Extended-release tablets
Drugs with gastric emptying delay
Complex absorption profiles

Files¶

File	Description
`julia.jl`	Julia implementation
`python.py`	Python implementation
`cli.json`	CLI specification