Acute Interaction of Baclofen in Combination With Alcohol in Heavy Social Drinkers

Alcoholism is a major public health problem in the United States, such that approximately 15.6 million people meet criteria for alcohol abuse or dependence, and over 800,000 received treatment for alcohol abuse or dependence in 2006 (SAMHSA, 2007). Despite the enormous impact of this disease on society, there are only three medications (disulfiram, naltrexone, and acamprosate) currently approved by the FDA for the treatment of alcohol dependence (e.g., Bouza et al., 2004; Heilig and Egli, 2006; Kiefer and Mann, 2005; Kranzler and Van Kirk, 2001) and given their limited efficacy there is a need for additional pharmacotherapies for alcohol dependence. The interaction of alcohol with the gamma-amino butyric acid (GABA)-ergic neurotransmitter system is well known (Grant and Lovinger, 2005) and targeting GABA-ergic neurotransmission has been considered as a potential treatment strategy for alcohol dependence (Johnson et al., 2005; Heilig and Egli, 2006). Baclofen, a GABA-B receptor agonist, has attracted considerable attention as a potential medication not only for alcoholism (Addolorato et al., 2006a; Colombo et al., 2004; Heilig and Egli, 2006; Johnson et al., 2005; Kranzler, 2000), but also for other addictive disorders (Cousins et al., 2002). There is encouraging preclinical evidence in laboratory rodents that baclofen decreases 1) alcohol withdrawal symptoms (Colombo et al., 2000; Knapp et al., 2007), 2) acquisition and maintenance of voluntary alcohol consumption (Colombo et al., 2000, 2002; Daoust et al., 1987), 3) alcohol consumption associated with alcohol deprivation (Colombo et al., 2003a, 2006), 4) alcohol self-administration (Anstrom et al., 2003; Besheer et al., 2004; Liang et al., 2006; Walker and Koob, 2007), and 5) responding for alcohol during extinction, suggestive of decreased motivation to obtain alcohol (Colombo et al., 2003b; Maccioni et al., 2008). However, not all preclinical studies have reported that baclofen produces a reduction in alcohol consumption or self-administration (e.g., Colombo et al., 2005; Czachowski et al., 2006; Moore et al., 2007; Petry, 1997; Smith et al., 1999; Tomkins and Fletcher, 1996). Nonetheless, the preclinical literature suggests that baclofen may have therapeutic efficacy for alcoholism. Several studies have been conducted in humans to evaluate the efficacy of baclofen for the treatment of patients with alcohol problems. One of the first studies used an open-label design in 10 alcohol-dependent patients (Addolorato et al., 2000) and found that maintenance on 30 mg/day of baclofen for 4 weeks decreased alcohol craving in the 9 patients who completed the study, with 7 patients maintaining total abstinence. Similar positive findings were obtained in two subsequent studies, both of which maintained alcohol-dependent patients on 30 mg/day of baclofen (Addolorato et al., 2002a; Flannery et al., 2004). These findings were recently extended and confirmed in a larger randomized clinical trial among alcohol-dependent patients with liver cirrhosis who were treated with either baclofen (30 mg/day) or placebo for 12 weeks (Addolorato et al., 2007). In all of these studies, side effects of baclofen were minimal and retention was excellent. Further, there have been two case reports showing that high doses of baclofen (100–140 mg/day) were effective in reducing alcohol craving and consumption (Ameisen, 2005; Buckman, 2007). Lastly, several small pilot studies have reported that baclofen (30 mg/day) reduces alcohol withdrawal symptoms in alcohol-dependent patients (Addolorato et al., 2002b, 2003, 2006b). Despite the promising preclinical and clinical findings to date suggesting that baclofen may be effective for treating alcohol dependence, there is a paucity of human laboratory studies assessing the interaction of baclofen and alcohol. Human behavioral laboratory studies can play an important role in the early stages of the medication development process for drug and alcohol abuse (Cousins et al., 2002; O’Brien and Gardner, 2005), particularly for assessing the safety of a candidate medication when administered alone and in combination with alcohol, as well as to elucidate the therapeutic mechanism. Baclofen is a centrally acting muscle relaxant approved by the FDA for the alleviation of signs and symptoms of spasticity; while the usual dose range is between 40–80 mg daily in divided doses, much higher doses have been used for the treatment of spasticity with a good safety profile (Aisen et al., 1992). Baclofen is also known to have anxiolytic effects (Breslow et al., 1989; Drake et al., 2003; Jamous et al., 1994), even among a population of alcoholic patients (Krupitsky et al.,1993), and these anxiolytic effects have been hypothesized to reduce alcohol craving and drinking. In fact, several studies have observed a reduction in anxiety in baclofen-treated alcohol-dependent patients (Addolorato et al., 2002a, 2006b, 2007;Flannery et al., 2004). Alternatively, baclofen may reduce alcohol craving and drinking by reducing the positive effects of alcohol, including the stimulant effects (Cousins et al., 2002), or by enhancing the negative effects of alcohol, including sedation. Despite these potential benefits, the sedative and anxiolytic effects of baclofen also raise concerns about the safety of baclofen in combination with alcohol and its abuse liability (Heilig and Egli, 2006). The purpose of the present study was to comprehensively assess the acute behavioral and physiological effects of baclofen (0, 40, 80 mg) alone, and in combination with an intoxicating dose of alcohol (0.75 g/kg) in non-treatment seeking heavy social drinkers. Specifically, we wanted to address the issues related to the safety profile of baclofen alone and in combination with alcohol, as well as the behavioral effects of baclofen that might elucidate the nature of its putative pharmacotherapeutic effect.