al., 2000; Schoedel et al., 2004). The CYP2A6*1×2 allele is a duplication variant that is associated with higher rates of nicotine metabolism than the wild-type CYP2A6 (Rao et al., 2000). The CYP2A6*1B variant is associated with approximately a 20% higher clearance of nicotine and 30% greater nicotine-metabolite ratio (Mwenifumbo et al., 2008b). It should be noted that many new CYP2A6 alleles are being identified and characterized in different populations, indicating that the proportion of those with slower and faster nicotine metabolism, detected by genetic testing, is increasing over time (Ho et al., 2008; Mwenifumbo et al., 2008a). A listing of CYP2A6 alleles and corresponding activity is provided in Table 1.
