Acute and chronic administration of a low-dose combination of topiramate and ondansetron reduces ethanol's reinforcing effects in male alcohol preferring (P) rats.

Topiramate (a GABA/glutamate modulator) and ondansetron (a serotonin-3 antagonist) have shown promise as treatments for alcohol use disorders (AUDs), although efficacy is modest/variable for both medications. We recently showed in animal models of consumption and relapse that acute treatment with a combination of these medications was more efficacious than either alone. To determine whether the mechanism for its beneficial effects is through modulation of ethanol's reinforcing effects, we measured the effect of this combination in male alcohol preferring (P) rats (N = 22) responding for ethanol under a progressive-ratio (PR) schedule. Low doses, which either do not affect (ondansetron; 0.001 mg/kg) or only modestly affect (topiramate; 10 mg/kg) alcohol-related behaviors on their own, were selected in an attempt to maximize their combined efficacy while minimizing potential side effects. In addition to acute treatment (1 day), the effects of chronic administration (10 days) were examined in an attempt to model human treatment approaches. The effects of the combination were compared with the low dose of topiramate alone hypothesizing that the combination would be more efficacious than topiramate alone. Although both topiramate and the combination similarly reduced PR responding for ethanol following acute treatment and during the initial phase of chronic treatment (Days 1-5), after repeated administration (Days 6-10), only the combination produced a sustained reduction in ethanol-maintained responding. These results suggest an advantage of the combination over topiramate alone at producing a sustained reduction in ethanol's reinforcing effects following prolonged treatment, and lend further support for its use as a potential treatment for AUDs.