HiguchiModell

The Higuchi model, known in German as the Higuchi-Modell, is a mathematical description of drug release from solid matrices by diffusion. It is a foundational model in pharmaceutics, used to analyze diffusion-controlled release from matrix-type dosage forms such as tablets and implants.

The model rests on several assumptions: the drug is initially uniformly distributed within a non-swelling, non-eroding matrix of constant diffusivity; the geometry is planar (a slab) or effectively so; the surrounding medium maintains sink conditions; and the drug concentration in the matrix remains high relative to its solubility. Under these conditions the cumulative amount of drug released, M_t, is proportional to the square root of time, M_t ∝ t^1/2. In planar geometry this is often expressed as M_t = k_H t^1/2, where k_H is the Higuchi release rate constant; it depends on factors such as the diffusion coefficient D, the drug solubility Cs in the matrix, and the exposed surface area.

Applications include the preliminary characterization of diffusion-dominated release from matrix tablets and similar systems, guiding formulation design and interpretation of in vitro dissolution data. The model is particularly useful for early-stage screening and for comparing release profiles across formulations.

Limitations arise when swelling, erosion, dissolution of the matrix, non-planar geometries, or multiple release mechanisms become relevant, as these violate core assumptions. In such cases alternative models (for example Korsmeyer–Peppas) may provide better descriptions. Despite its simplifications, the Higuchi model remains a standard reference in diffusion-controlled release analysis.