All open-label trials were excluded, as was a retrospective chart review (Raskind et al., 2002) and a study that did not use an overall PTSD outcome measure (Taylor et al., 2006).2 See Table 3-1 for a summary of the two included clinical trials.
The committee identified a small number of studies examining the effects of anticonvulsants such as topiramate, tiagabine, and lamotrigine on PTSD. Most studies were excluded because they were open label or uncontrolled. Participants in the anticonvulsant studies suffered a variety of traumas including combat-related, sexual and physical abuse and/or assault, witnessing, and serious accident or injury. The mean age of study participants was 43 years old with a range from late-20s to mid-50s. One study reported the duration of illness to be an average of 13 years, and duration of illness and time since trauma was not reported in the other studies (Davidson et al., 2007). In one study ethnicity was not reported, and the others had predominantly black (71 percent) and white (90 percent) populations, respectively.
All studies were double-blinded and included a placebo control. Treatment length was 12 weeks for all studies. Only one study conducted follow-up after completion of treatment (1-year follow-up) (Hertzberg, 1999). All studies measured adverse events associated with the treatment condition. The main PTSD outcome measures used in the selective serotonin reuptake inhibitors (SSRIs) studies were CAPS-Total and SI-PTSD.
Of the three randomized controlled trials (RCTs), two had major limitations including high differential and total dropout rates (Davidson et al., 2007; Tucker et al., 2007) and neither showed a positive effect on a primary PTSD outcome. The third qualifying RCT showed a positive effect of treatment with lamotrigine, but the trial was too small (a total of 15 patients) to reach statistical significance or estimate an effect size (Hertzberg et al., 1999).
Synthesis: The committee found the overall body of evidence regarding anticonvulsants to be scant and low quality. The committee is uncertain about the presence of an effect, and believes that future well-designed studies will have an important impact on confidence in the effect and the size of the effect.