Combination pharmacotherapy: a mixture of small doses of naltrexone, fluoxetine, and a thyrotropin-releasing hormone analogue reduces alcohol intake in three strains of alcohol-preferring rats.

It is common to treat some diseases with more than one medication simultaneously. Since more than one neurotransmitter system is involved in alcohol-seeking behaviour, then a therapeutic approach that targets more than one system should be more effective in reducing alcohol intake than one addressing a single system. To test this hypothesis, we compared the efficacy of low doses of individual drugs reported to reduce voluntary alcohol drinking to the efficacy of a mixture of these agents at the same low doses in reducing alcohol intake in three strains of alcohol-preferring rats (P, HAD, and Fawn-Hooded). After establishment of a stable baseline for alcohol intake in a continuous access paradigm, each rat received separate single i.p. injections of relatively low doses of either naltrexone (2.0 mg/kg), fluoxetine (1.0 mg/kg), the thyrotropin-releasing hormone analogue TA-0910 (0.2 mg/kg), a mixture of all three drugs, or the vehicle at 09:30. Each rat received all treatments, with an inter-injection washout period of at least 3 days. Alcohol and water intakes were measured at 6 and 24 h, and food intake was measured at 24 h, after the injection. Our results show that individual drugs did not significantly affect food, water, or alcohol intake. However, the mixture significantly reduced alcohol intake in all three strains, but had no effect on food intake. Similar results were obtained when the HAD rats received an oral dose of the individual drugs or the mixture. When P rats were given an i.p. injection of the mixture for 10 consecutive days, there was a continued suppressing effect. These findings show that a combination treatment designed to target simultaneously serotonergic, dopaminergic, and opioidergic systems can reduce alcohol intake, even though the doses of the individual drugs in the mixture are relatively low and ineffective when given singly.