Bringing the Light to Photostability in Three Parts

Part 1: Basic Requirements – Setting the Stage

ICH Guidance Q1B was published in 1996 describing a harmonized approach to photostability studies.  Although it has been 20+ years since its publishing, questions still arise on how to execute a photostability study and how to interpret the results based on ICH stability guidelines.  In this blog series, I will address common questions and detail how a photostability study is executed.  At Alcami, photostability is conducted at two laboratory sites: Wilmington, NC and St. Louis, MO.

A photostability study is performed using either a full spectrum light source that produces a spectrum similar to D65/ID65 emission standard, or two separate light sources: one for near UV radiation with a spectral distribution from 320 nm to 400 nm with a maximum energy emission between 350 nm and 370 nm, and a second light source that is a cool white fluorescent lamp designed to produce an output similar to that specified in ISO 10977.  Regardless of which approach is taken, the objective is to expose samples to an integrated amount of NLT 200 Watt·hrs/m² of near-ultraviolet energy and NLT 1.2 million lux·hours of visible light. 

The description of the light sources may sound complex, but since 1996 several vendors have produced off-the-shelf light sources and chambers to meet these ICH requirements.  The intensity of the light sources is not mentioned in the guidance; however, the intensity impacts the time needed to achieve the required exposure levels.  At Alcami, just under 10 days is required to achieve the required exposure levels.   Higher intensity light sources are available on the market that would result in shorter exposure times, such as Xenon arc lamps.  However, higher intensity light sources typically result in high heat outputs that can be difficult to control, resulting in thermal degradation of a material.  Using the photostability chambers at Alcami, the temperature can be controlled at either 25°C +/- 2C or at 5°C+/- 3°during the exposure of either API or drug product.

Stay tuned for my next blog post “Part 2: Forced Degradation Studies to Support Photostability” to dive deeper into photostability studies.