showed in guinea pig ileal smooth muscle in vitro that both peppermint oil and its constituent menthol were capable of blocking calcium channels. 7, 8, 11Įffects on Gastrointestinal Tract Neuromotor FunctionĮvidence suggests that peppermint oil acts as a smooth muscle relaxant. Peppermint oil metabolites are excreted in the urine in part as glucuronic acid conjugates with ≥ 50% of a 100 mg oral dose of menthol appearing in urine as menthol glucuronide. Following biliary excretion, menthol glucuronide undergoes enterohepatic circulation. 9, 10 Therefore there is the potential for pharmacogenomics and other substances which impact either CYP2A6 or UGT2B7 activity to alter peppermint oil’s concentration-time curve. 3, 5 In particular, data show the importance of both CYP2A6 (the major P450 enzyme involved in menthol hydroxylation) and UGT2B7 expression in determining menthol clearance. 2, 3 Menthol is excreted into bile as menthol glucuronide. Menthol is primarily metabolized in the liver via hepatic microsomal P450 enzymes and subsequently undergoes biotransformation via UDP-glucuronosyltransferases. 8 In addition, development (reflected by age) may impact the pharmacokinetics of menthol as we showed in a pilot study in healthy children administered peppermint oil. 6 A L-menthol preparation sprayed directly onto the gastric mucosa was rapidly absorbed with peak concentrations reached within one hour after administration. 7 However, as noted, pharmacokinetics are greatly dependent on the formulation used. 6 In healthy adults, an oral dose of 100 mg of menthol results in an average peak blood concentration of 16.7 ± 5.5 μmol/L and an apparent elimination t 1/2 of 56 ± 8 min. The delayed release formulation did not alter the absorption half-life or total area under the curve. non-delayed release formulations) altered menthol urinary pharmacokinetics by increasing the apparent lag time and time to peak plasma concentrations. 5 Though done in a small study (n=13), delayed release formulations of peppermint oil (vs. ![]() 3, 5, 6 However, when taken in capsule form designed for delayed release, approximately 70% reaches the colon. 3, 4 Studies in rats and limited data in humans demonstrate that peppermint oil is rapidly absorbed. 3 The main constituent and active ingredient of peppermint oil appears to be menthol although it contains a large number (greater than 80) of other components. Pharmacokinetic data relating to peppermint oil in humans are limited.
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