Dantrolene sodium is a direct-acting skeletal muscle relaxant. Dantrolene sodium for injection is indicated, along with suitable supportive measures, for the management of sudden, severe hypermetabolism of skeletal muscle typical of malignant hyperthermia crises in patients of any age. The formulation scanned in this work was designed to be injected intravenously. Intra-lot and inter-lot variability in the spectra of REVONTO™ (dantrolene sodium) was measured in the Drug Quality Study (DQS) using Fourier transform near-infrared spectrometry (FTNIR). Spectra of 69 vials from lot 20REV01A contained two groups (n1=56 vials, n2=13 vials) when scanned with an FTNIR. The two groups of spectra in lot 20REV01A were found to be 66.7 SDs apart using a subcluster detection test, suggesting that the two groups were manufactured differently. As a result, all available samples of dantrolene were examined. A library of spectra of 141 vials of dantrolene from 4 lots were found to contain 3 separate groups, also suggesting that different vials contain different materials.