IVRT — In Vitro Release Testing

IVRT is a laboratory method that measures the rate at which an active ingredient is released from a topical or semisolid product — such as a cream, gel or ointment. The product is applied to one side of an inert synthetic membrane in a diffusion cell, and the amount of drug crossing into the receptor medium is measured over time.

The result is a release rate that characterizes the product and is sensitive to formulation and manufacturing changes.

IVRT (In Vitro Release Testing) measures how fast a drug is released from a formulation across an inert synthetic membrane, characterizing the product itself. IVPT (In Vitro Permeation Testing) measures how much drug permeates through actual skin, characterizing delivery through the skin barrier.

In short: IVRT reflects formulation release and is often used to detect changes, IVPT reflects biologically relevant penetration. Many programs use both.

IVRT provides a sensitive, quantitative measure of a product’s release behaviour, which reflects its formulation and microstructure. Because the release rate changes when the formulation or manufacturing process changes, IVRT is valuable for comparing prototypes during development, confirming batch-to-batch consistency, and supporting sameness assessments after post-approval changes.

IVRT is typically run using vertical diffusion cells (Franz-type cells), with the product in the donor chamber separated from the receptor medium by an inert synthetic membrane rather than skin. The membrane is chosen so it does not limit release. Temperature and stirring are controlled, and the receptor fluid is sampled at set time points to build the release profile.

In an IVRT study, the cumulative amount of drug released is measured at several time points and typically plotted against the square root of time. The slope of the linear portion gives the release rate. Comparing the release rate of a test product against a reference within accepted limits is the basis for sameness or equivalence assessments.

IVRT is used to compare the release behaviour of a test product against a reference, supporting Q3 (microstructure) sameness because differences in microstructure change how a drug is released.

Regulators reference IVRT in guidance on post-approval changes to semisolids and, together with other methods, in approaches to topical bioequivalence. Specific requirements vary by product and should be confirmed against current regulatory guidance.

An IVRT method must be developed and validated to show it is sensitive and discriminating — able to detect meaningful differences between formulations while giving reproducible results. Method development covers the membrane, receptor medium and study design; validation demonstrates the method’s discrimination, reproducibility and robustness before it is used for comparative or regulatory work.

Dissolution testing measures how a solid oral dosage form, such as a tablet or capsule, dissolves. IVRT is the semisolid analogue: it measures how fast a drug is released from a topical product across a membrane. Both characterize release, but the equipment, membranes and study design differ because the dosage forms are different.

During development, IVRT is used to screen and optimize formulations and to confirm consistency between batches. For regulatory purposes, a validated IVRT method can support sameness assessments after manufacturing or formulation changes and can form part of a topical bioequivalence approach. A regulatory study is designed and validated to a higher standard than an exploratory one.

It depends on the market and how the data is used. In the EU, IVRT supports the quality and equivalence dossier under the EMA guideline on locally applied, locally acting cutaneous products, and it is also used for GMP quality-control of manufacturing batches — and because GLP is not the EMA’s enforceable framework for this work, IVRT is performed within the pharmaceutical quality system (GMP). For US FDA (ANDA) submissions, IVRT and IVPT bioequivalence studies are instead expected to be conducted in a manner compatible with GLP principles.

Zelmic operates an EU GMP-compliant facility in Lund with integrated quality control laboratories, so IVRT can be run under GMP — the framework that applies for EU submissions and for QC of manufacturing batches — with validated, discriminating methods and controlled documentation. Zelmic’s laboratory is also registered with the US FDA; registration is not an FDA inspection or approval, but it means data generated at Zelmic can support submissions to the FDA. The exact quality framework for a given study is set with the client according to its target markets and regulatory strategy.

Zelmic, based in Lund, Sweden, is a specialized CRO/CDMO offering IVRT and IVPT alongside topical and transdermal formulation development, analytical chemistry and EU GMP manufacturing. Zelmic develops and validates IVRT methods and runs comparative studies to support formulation development, optimization and regulatory programs for topical products.