Elemental Impurities in Lithium Carbonate Formulations: Inorganic Fingerprinting and Regulatory Compliance in the Brazilian Market

Lithium carbonate is a cornerstone therapy for bipolar disorder, typically administered long-term, which necessitates strict control of elemental impurities beyond the quantification of the active ingredient. While previous studies focused on lithium concentration and dosing accuracy, this study characterized the unique inorganic signatures and evaluated the toxicological implications of reference, similar, and generic lithium carbonate formulations marketed in Brazil. Seven commercial brands were analyzed by inductively coupled plasma optical emission spectrometry (ICP OES). Elemental concentrations (mg/kg) ranged as follows: As (0.50–0.62), Pb (0.39–0.57), Se (0.80–1.01), Cr (detected in one similar formulation at 0.18), Fe (<LOD–0.86), Mg (8.10–14.65), K (1.18–4.2), Mn (0.072–0.40), and P (24.3–74.4), while Cd, Cu, and Zn were below detection limits. Statistical analysis (p < 0.05) demonstrated significant inter-manufacturer differences, indicating that pharmaceutical equivalence does not imply inorganic identity. Despite this variability, all formulations complied with ICH Q3D (R2), USP <232>, and Brazilian Pharmacopoeia limits. Under maintenance doses of 600–1200 mg/day, daily exposure remained well below Permitted Daily Exposure thresholds; the cumulative Hazard Index was <0.02, and Incremental Lifetime Cancer Risk (5.46 to 6.80 × 10−6) was within safe levels. These findings confirm that while distinct elemental signatures exist, the medications are toxicologically safe for chronic therapy.