Revisiting Baclofen for the Treatment of Severe Chronic Tinnitus

tinnitus to begin with. Another was that the study was potentially underpowered statistically due to the inclusion of several different types of tinnitus, some of which might not have responded to the drug (Møller, 1997). The possibility that the study was underpowered was carefully acknowledged by the authors themselves, who performed power calculations for different scenarios (Westerberg et al., 1996). In addition, Westerberg et al. (1996) apparently used racemic baclofen (i.e., a mixture of the land d-isomers of baclofen, also known as Rand S-isomers), which was the only licensed form in 1996 (Szczepaniak and Møller, 1995), and d-baclofen has been reported to be less potent than l-baclofen in reducing toneand click-evoked hyperexcitability in neurons of the inferior colliculus (Szczepaniak and Møller, 1995, 1996). In fact, a number of studies have reported that d-baclofen can reduce the effects of l-baclofen. This has been reported in the trigeminal nucleus (Terrence et al., 1983; Fromm et al., 1990), but not in the hippocampus or neocortex (Howe and Zieglgänsberger, 1986). In the spinal cord, d-baclofen has been reported to antagonize the effects of l-baclofen (Sawynok and Dickson, 1984, 1985). In a double blind crossover trial with 15 patients suffering from trigeminal neuralgia, in 9 patients l-baclofen was reported to be five times more effective in relieving the symptoms than racemic baclofen (Fromm and Terrence, 1987). In addition, the adverse side effects of l-baclofen were better tolerated than those of the racemic baclofen (Fromm and Terrence, 1987). Although the idea that d-baclofen is an antagonist, at least at some GABA B receptors, is still unresolved (Froestl, 2010), at the very least it can be concluded that its agonist effects are much less potent than l-baclofen, which appears to be the case in the inferior colliculus (Szczepaniak and Møller, 1995, 1995). This Revisiting baclofen for the treatment of severe chronic tinnitus