Co-administration of subeffective anxiolytic doses of diazepam and hydroxyzine in elevated zero-maze in mice

Benzodiazepines are from the most common drugs which are used for treatment of anxiety disorders. There are other drugs with antianxiety properties including antihistamines such as hydroxyzine, too. Body of evidence show that co-administration of two drugs which act through different mechanisms, makes the dose of each drug to be reduced, while preserving the desired effect with less adverse drug reactions. The aim of this study was to see whether co-administration of subeffective antianxiety doses of diazepam and hydroxyzine has any antianxiety effect in elevated zero-maze (EZM) in mice.

To find the highest subeffective dose of each drug, different doses of hydroxyzine from 1.5 to 24 mg/kg and diazepam in doses of 0.25, 0.5 and 1 mg/kg were injected to male mice. Thirty minutes later, the animals were placed on EZM and various parameters of anxiety were recorded by a camera to assess later. After determination of subeffective antianxiety dose of the drugs, co-administration of hydroxyzine and diazepam was done and the anxiety parameters were measured.

In co-administration of 0.25 mg/kg of diazepam and 12 mg/kg hydroxyzine, as subeffective antianxiety doses of either drug, there were not any significant differences in main anxiety parameters, i.e., time spent in open areas and open area entries compared to control group. Hence, no anxiolytic effect was seen.

It seems that subeffective doses of diazepam and hydroxyzine may not have any facilitating or synergistic effect on each other in antianxiety responses in mice.