biostudies-literaturePritts JDCenter for Drug Evaluation and Research185-193https://www.ebi.ac.uk/biostudies/studies/S-EPMC12913286biostudies-literatureUnknown43(1)<h4>Background</h4>While photostability testing conditions for biologics are often based on small molecule standards, the unique characteristics of proteins necessitate a deeper understanding of appropriate testing and controls. This study examines the effects of light stress on various presentations of somatropin, a therapeutic growth hormone.<h4>Methods</h4>Somatropin was exposed to light in lyophilized, reconstituted, and diluted forms. Quality attribute changes were analyzed using size exclusion chromatography, micro-fluidic imaging, imaged capillary isoelectric focusing, and liquid chromatography mass spectrometry (LC-MS).<h4>Results</h4>Light stress increased high molecular weight species (HMWS), particularly in liquid formulations, as shown by size exclusion chromatography (LyophiliPharmaceutical researchPhysicochemical Differences Observed in Photostability Studies of Lyophilized, Reconstituted, and Diluted Somatropin.PMC12913286FD999999Ortega-Rodriguez URao VAPritts JDfalsePhysicochemical Differences Observed in Photostability Studies of Lyophilized, Reconstituted, and Diluted Somatropin.<h4>Background</h4>While photostability testing conditions for biologics are often based on small molecule standards, the unique characteristics of proteins necessitate a deeper understanding of appropriate testing and controls. This study examines the effects of light stress on various presentations of somatropin, a therapeutic growth hormone.<h4>Methods</h4>Somatropin was exposed to light in lyophilized, reconstituted, and diluted forms. Quality attribute changes were analyzed using size exclusion chromatography, micro-fluidic imaging, imaged capillary isoelectric focusing, and liquid chromatography mass spectrometry (LC-MS).<h4>Results</h4>Light stress increased high molecular weight species (HMWS), particularly in liquid formulations, as shown by size exclusion chromatography (Lyophili2026-01-01T00:00:00Z2026 Jan2026-07-16T06:57:12.538Z2026-07-09T13:10:53.359ZS-EPMC129132864140268210.1007/s11095-025-03986-1