ABSTRACT: BACKGROUND:The development of drug delivery systems has improved the therapeutic and toxic properties of existing drugs in therapy. Microemulsion systems are novel vehicles for drug delivery, which have been developed in recent years. These systems are currently of interest to the pharmaceutical scientist because of their considerable potential to act as drug delivery vehicles by incorporating into a wide range of drug molecules. Although these systems improved solubility and bioavailability of drugs, they may have potential toxic effects on the body organs. OBJECTIVES:The purpose of this study was to examine a possible hepatotoxic and nephrotoxic effect of lithium carbonate microemulsion (LCME) in a mice model. MATERIALS AND METHODS:Eighty male Swiss albino mice were randomly allocated to eight experimental groups, as follows: Group 1, as negative control group were treated orally with normal saline (0.9% NaCl); Group 2, received microemulsion base without drug as control group; Groups 3 to 5, received lithium carbonate (LC) solution in doses of 50, 100, and 200 mg/kg, respectively; Groups 6 to 8, received LCME orally in doses of 50, 100, and 200 mg/kg, respectively. All drugs were administered orally for ten consecutive days. Serum glutamate pyruvate aminotransferase (SGPT), serum glutamate oxaloacetate aminotransferase (SGOT), alkaline phosphatase (ALP), blood urea nitrogen (BUN), and plasma creatinine (Cr), as markers of liver and kidney toxicity in treated mice, were measured. Furthermore, the changes of tissue were assessed by histopathologic examination. RESULTS:The findings showed that serum activity of ALP, SGOT, and SGPT and the levels of BUN and Cr in microemulsion base group was greater than normal saline group. However, this difference was not significant. Administration of LC and LCME in all doses resulted in a significant increase in the levels of BUN and serum activity of SGOT and SGPT in comparison to normal saline group (P < 0.05). Histopathological changes were observed in mice treated with LC or LCME. CONCLUSIONS:This study showed that subacute oral administration of different doses of LCME with severe toxicity in comparison to the same dose of LC.