Anxiolytic activity of chloral hydrate and hydroxyzine

The combination of chloral hydrate and hydroxyzine is given frequently to anxious pediatric dental patients. In order to observe and quantify the anxiolytic effects of these drugs given alone and in combination, highly explorative male C57/black mice were tested using the light/dark test box after injecting subhypnotic doses for increased transitions between the light and dark side of the test box. Fifty-one mice were subjected individually to a 10-min test in the box for dose responses following the i.p. administration of 32-, 64-, and 132-mg/kg doses of chloral hydrate; 1-, 4-, 7-, and 10-mg/kg doses of hydroxyzine; or a combination of each of these doses of hydroxyzine and chloral hydrate. The automated test box recorded the number of times a mouse crossed between the two chambers. Doses of chloral hydrate 132 mg/kg and hydroxyzine 1 mg/kg resulted in significantly increased transitions. None of the combinations studied produced significantly increased transitions when compared with the effective doses identified for each individual drug. The paradigm did not support the hypothesis that the anxiolytic effects of chloral hydrate and hydroxyzine are additive or synergistic.