Shelf Life vs. Retest Date - What's the Difference?

Both shelf life and the retest date are based on stability data, but they have different applications and implications, especially for the drug substance versus the drug product. So what exactly is the difference, and which regulatory requirements are most relevant?

Definitions per ICH

Authoritative definitions are found in ICH Q1A(R2) – Stability Testing of New Drug Substances and Products.

• Shelf life (also referred to as expiration dating period)
  The time period during which a drug product is expected to remain within the approved shelf life specification, provided that it is stored under the conditions defined on the container label.

• Re-test date
  The date after which samples of the drug substance should be examined to ensure that the material is still in compliance with the specification and thus suitable for use in the manufacture of a given drug product.

Shelf life therefore applies to finished medicinal products (drug product) and is the period during which a product remains within the approved specification under defined storage conditions. Up to the expiry date, the product must meet the approved specifications. Important: a drug product may not be used after its expiry date. Extending the shelf life is only possible through a regulatory change supported by adequate stability data, not by simply “retesting” individual batches.

By contrast, the re-test date is used for drug substances: once this date has passed, the batch can be re-examined and, if compliant, continue to be used. In both cases, formal stability studies are the basis for setting the period.

ICH Q7 – Good Manufacturing Practice Guide for Active Pharmaceutical Ingredients elaborates on practice. A retest is common; an expiry date for APIs is the exception.

• Retest Date
  The date when a material should be re-examined to ensure that it is still suitable for use.
• 11.61 An API expiry or retest date should be based on an evaluation of data derived from stability studies. Common practice is to use a retest date, not an expiration date

This retest concept differs from the expiry date of a drug product.

Draft ICH Q1 (Step 2, April 2025)

The draft of the new ICH Q1 – Stability testing of drug substances and drug products (Step 2) defines shelf life more broadly for both drug substances and drug products, while the definition of re-test date is carried over unchanged:

• Shelf life: The time period during which a drug substance or drug product is expected to remain within the approved shelf life specification, provided that it is stored under the conditions defined on the label.
• Re-test Date: The date after which samples of the drug substance should be examined to ensure that the material is still in compliance with the specification and thus suitable for use in the manufacture of a given drug product.