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Novel ileocolonic release peppermint oil 131 6 Table 6.5 Adverse events occurring after administration of a single 182 mg peppermint oil dose. Small-intestinal release PO Ileocolonic release PO N =8 N =8 Acid regurgitation , N (%) 1 (12.5) 0 (0) Fecal urgency , N (%) 1 (12.5) 0 (0) Headache , N (%) Mild Moderate/severe 0 (0) 0 (0) 2 (25) 0 (0) Altered fecal odor , N (%) 0 (0) 2 (25) Vital sign abnormalities , N (%) 0 (0) 0 (0) PO; peppermint oil, N ; number. N =8 (total group). Altered fecal odor implied a peppermint oil odor. Discussion This is the first study to investigate a novel ileocolonic release peppermint oil formulation and to compare its pharmacokinetic parameters, safety, and tolerability with the small-intestinal release peppermint oil formulation currently available. Our results demonstrate that ileocolonic release peppermint oil soft capsules have a significantly delayed lag time (T lag ) and reach their peak concentration significantly later (T max ) than small-intestinal release peppermint oil capsules. These findings point to the release of peppermint oil in a more distal part of the human gastrointestinal tract, the colon most presumably. Although different in release kinetics, a single dose of both formulations of peppermint oil can be considered bioequivalent regarding exposure in healthy volunteers, because the 90% confidence interval (CI) for the log-transformed parameter ratios (small-intestinal/ileocolonic release) is between the 80-125% confidence interval, the standard bioequivalence criterion as stated in the FDA and EMA guidelines on the investigation of bioequivalence. 30,31 Several authors have previously reported on the pharmacokinetic parameters of small- intestinal release peppermint oil, often referred to as enteric-coated capsules: White et al . found a mean T max of 5 and 2.8 hours for menthol-glucuronide after three Colpermin® or Mintec® capsules were taken, containing 0.2 ml peppermint oil each and a mean L-menthol concentration of 110 mg and 117 mg respectively. 19 Mascher et al. found a mean T max of 3 hours and a mean menthol C max of 1196 ng/ml after two Enteroplant® capsules were taken, containing 90 mg of peppermint oil each. 34 Our findings for the small-intestinal release peppermint oil capsules are in line with both White et al. and Masher et al. in terms of T max found, although the C max differed slightly. A possible explanation for this modest discrepancy is that different small-intestinal