Metabolism and Disposition of 2-Ethylhexyl-p-methoxycinnamate Following Oral Gavage and Dermal Exposure in Harlan Sprague Dawley Rats and B6C3F1/N Mice and in Hepatocytes in vitro
1. 2-Ethylhexyl-p-methoxycinnamate (EHMC) is commonly used as an ingredient in sunscreens, resulting in potential oral and dermal exposure in humans. 2. Clearance and metabolism of EHMC in hepatocytes and disposition and metabolism of EHMC in rodents following oral (8 to 800 mg/kg) intravenous (IV) (8 mg/kg), or dermal (0.8 to 80 mg/kg representing 0.1 to 10% formulation concentration) exposure to [(14)C]EHMC were investigated in rats and mice. 3. EHMC was rapidly cleared from rat and mouse hepatocytes (half-life ≤ 3.16 min), and less rapidly (half-life ≤ 48 min) from human hepatocytes. 4. [(14)C]EHMC was extensively absorbed and excreted primarily in urine by 72 h after oral administration to rats (65-80%) and mice (63-72%). Gavage doses to rats were excreted to a lesser extent (3-8%) in feces and as CO2 (1-4%). Radioactive residues in tissues were <1% of the dose. There were no sex, route, or species differences in disposition in rats. 5. Following dermal application, 34-42% of an 8 mg/kg dose was absorbed in rats, and 54-62% in mice in 72 h. 6. Among numerous urinary metabolites associated with hydrolysis of the ester, two potential reproductive and developmental toxicants, 2-ethylhexanol and 2-ethylhexanoic acid were produced by metabolism of EHMC.