1997; Neufeld et al. 1996; Treves and Neufeld, 1996; Olesen et al. 1995; Risby et al. 1995; Haring et al. 1994; Welch et al. 1994; Gunther et al. 1993;

Tiihonen et al. 1991] providing information on EEG click here changes in 565 patients studied. In total, 347 patients of the 565 had an abnormal EEG. The reported prevalence of EEG changes in people taking clozapine varied from 25% [Neufeld et al. 1996] via 53% [Freudenreich et al. 1997; Risby et al. 1995; Haring et al. 1994] to 100% (small Inhibitors,research,lifescience,medical populations) [Malow et al. 1994; Tiihonen et al. 1991]. These studies have been summarized in Table 1. Table 1. Summaries of reports on the prevalence of clozapine-associated electroencephalogram (EEG) abnormalities. Although a spectrum of EEG abnormalities was observed Inhibitors,research,lifescience,medical in association with clozapine, the most common EEG abnormality was nonspecific generalized slowing [Chung et al. 2002; Schuld et al. 2000; Freudenreich et al. 1997; Treves and Neufeld, 1996; Haring et al. 1994; Welch et al. 1994] involving delta and theta waves (slow waves). Delta is the frequency range below 4 Hz, it is normally seen in deep sleep (slow wave sleep) in adults and is not usually seen in the awake adult. Theta is the frequency range from

4 to 8 Hz and can be observed in meditation and drowsy states. Theta waves are considered abnormal if they occur in excess in the awake Inhibitors,research,lifescience,medical adult [Alarcon et al. 2009]. Spike or sharp activity was present in a relatively smaller proportion. The effect Inhibitors,research,lifescience,medical of clozapine dose on EEG There was strong evidence of a dose-related effect on EEG, illustrated in the graph of proportion of patients with abnormal

EEG versus clozapine mean dose (see Figure 1). Figure 1. Proportion of patients with abnormal electroencephalogram (EEG) versus clozapine mean dose. Twelve studies contributed data to this weighted analysis; this enabled the size of each study to be taken into account, with larger studies carrying more weight which is proportional to the variance. One study [Freudenreich Inhibitors,research,lifescience,medical et al. 1997] included results for three subsets of patients based on different dose levels; these were included as three separate data points. The study by Malow and colleagues [Malow et al. 1994] already was excluded, as it was unclear how they identified their 10 patients for EEG analysis from a subset of 40 patients. (All 10 patients displayed EEG abnormality.) Another study [Silvestri et al. 1998] was also excluded, as the clozapine doses used or levels attained were not given. The mean clozapine dose and standard deviation were not specified in the studies by Welch and associates [Welch et al. 1994] and Olesen and associates [Olesen et al. 1995]. These data were calculated using the individual doses given in both studies. The spectrum of EEG abnormalities from general slowing to spike/sharp waves was grouped together. The circumference of the circle is proportional to the weight of the study in the regression model.