Ninety-day toxicity study of chloral hydrate in the Sprague-Dawley rat

Male and female Sprague-Dawley rats were administered drinking water containing 300, 600, 1200, or 2400 mg/L chloral hydrate for 90 days. A control group received distilled water only. No animals died during the study and no differences were observed in body weight gain or food and water consumption, except for males at the highest-dose level. Minor treatment-related effects were observed for organ weights and hematological parameters and these did not appear to be of toxicological significance. Some indications of toxicity were evident in the 2400 mg/L male group (equivalent to 168 mg/kg-day) including a significant decrease in food and water consumption and in weight gain. In addition, histopathological examination of these animals revealed an apparent increase in the incidence of focal hepatocellular necrosis. Increases in AST, ALT, and LDH, which occurred at several dose levels in males, but particularly at 200 mg/L, are consistent with the hepatocellular necrosis of minimal to mild severity diagnosed by microscopic examination. These liver changes, except for sporadic enzyme changes, were not seen in the female rats which actually consumed higher doses of chloral hydrate (e.g., 288 mg/kg-day at 2400 mg/L). On the basis of the mild liver toxicity (histopathological and clinical) observed in males at the highest doses (168 mg/kg-day), the no observed adverse effect level (NOAEL) for oral exposure of rats to chloral hydrate for 90 days is considered to be 96 mg/kg-day (600 mg/L).