In vitro Simulated Digestion and Microstructure of Peppermint Oil Nanoemulsion.

The variations in average particle size, zeta potential, free fatty acids (FFA) release rate, and the bioavailability of menthol under in vitro simulated digestion conditions of peppermint oil nanoemulsion were investigated. 3D confocal laser scanning microscopy and Cryo-scanning electron microscopy were used to observe the microstructure characteristics of peppermint oil nanoemulsion, which indicated that soybean protein was completely adsorbed at the oil-water interface of the nanoemulsion and presented a core shell structure. And the results indicated that FFA release rate and menthol bioavailability of peppermint oil nanoemulsion prepared by using high-pressure homogenization were much higher. In the simulated gastric digestion phase, the average particle size and the zeta potential of the nanoemulsion increased, and droplet polymerization appeared. After the simulated intestinal, the interfacial protein of nanoemulsion was hydrolyzed, and the oil droplets were digested, which resulted in the decreased particle size and increased absolute value of zeta potential.

An in silico investigation of menthol metabolism.

Prevalence of mentholated products for consumption has brought great importance to studies on menthol's metabolic pathways to ensure safety, design more potent derivatives, and identify therapeutic benefits. Proposed pathways of (-)-menthol metabolism based on metabolites found experimentally in previous works by Yamaguchi, Caldwell & Farmer, Madyastha & Srivatsan and Hiki et al. were not in agreement. This in silico approach is based on the three in vivo studies and aims to resolve the discrepancies. Reactions in the pathways are conjugation with glucuronic acid/sulfate, oxidation to alcohol, aldehyde & carboxylic acid, and formation of a four-membered/five-membered ring. Gas-phase structures, standard Gibbs energies and SMD solvation energies at B3LYP/6-311++G(d,p) level were obtained for 102 compounds in the pathways. This study provides a more complete picture of menthol metabolism by combining information from three experimental studies and filling missing links in previously published pathways.

Combination with l-Menthol Enhances Transdermal Penetration of Indomethacin Solid Nanoparticles.

This study designed the transdermal formulations containing indomethacin (IMC)-1% IMC was crushed with 0.5% methylcellulose and 5% 2-hydroxypropyl-ß-cyclodextrin by the bead mill method, and the milled IMC was gelled with or without 2% l-menthol (a permeation enhancer) by Carbopol® 934 (without menthol, N-IMC gel; with menthol, N-IMC/MT gel). In addition, the drug release, skin penetration and percutaneous absorption of the N-IMC/MT gel were investigated. The particle sizes of N-IMC gel were approximately 50-200 nm, and the combination with l-menthol did not affect the particle characterization of the transdermal formulations. In an in vitro experiment using a Franz diffusion cell, the skin penetration in N-IMC/MT gel was enhanced than the N-IMC gel, and the percutaneous absorption (AUC) from the N-IMC/MT gel was 2-fold higher than the N-IMC gel. On the other hand, the skin penetration from the N-IMC/MT gel was remarkably attenuated at a 4 °C condition, a temperature that inhibits all energy-dependent endocytosis. In conclusion, this study designed transdermal formulations containing IMC solid nanoparticles and l-menthol, and found that the combination with l-menthol enhanced the skin penetration of the IMC solid nanoparticles. In addition, the energy-dependency of the skin penetration of IMC solid nanoparticles was demonstrated. These findings suggest the utility of a transdermal drug delivery system to provide the easy application of solid nanoparticles (SNPs).

A Novel, Duodenal-Release Formulation of a Combination of Caraway Oil and L-Menthol for the Treatment of Functional Dyspepsia: A Randomized Controlled Trial.

OBJECTIVES: We conducted a randomized, placebo-controlled trial, which evaluated a novel formulation of caraway oil and L-menthol using microsphere-based site-specific targeting (COLM-SST) vs placebo in patients with functional dyspepsia (FD). METHODS: Adult men and women with FD defined by Rome III criteria were recruited. Patients were randomized to COLM-SST (25 mg of caraway oil and 20.75 mg of L-menthol per capsule, at 2 capsules per dose, twice per day) or placebo. Efficacy was measured at 24 hours, 2 weeks, and 4 weeks. Patients were allowed to take concomitant medications for their FD throughout the trial, and rescue medicines were allowed, 48 hours after start of dosing. RESULTS: Ninety-five patients were enrolled (mean age = 43.4 years; 75.8% women). At 24 hours, the active arm reported a statistically significant reduction in postprandial distress syndrome symptoms (P = 0.039), and a nonsignificant trend toward benefit of epigastric pain syndrome symptoms (P = 0.074). In patients with more severe symptoms, approximately 3 quarters of patients showed substantial global improvement (i.e., clinical global impressions), after 4 weeks of treatment, vs half in the control arm. These differences were statistically significant for patients with epigastric pain syndrome (P = 0.046), and trending toward significance for patients with postprandial distress syndrome (P = 0.091). There was no statistically significant difference between groups for Global Overall Symptom scores for the overall population at 2 and 4 weeks. Treatment emergent adverse events were mild to moderate, and no serious adverse events were reported. DISCUSSION: In patients taking their usual medications for FD, COLM-SST provided rapid relief (within 24 hours) and relief of severe FD symptoms. It was safe and well tolerated.

Bioavailable Menthol (Transient Receptor Potential Melastatin-8 Agonist) Induces Energy Expending Phenotype in Differentiating Adipocytes.

Recent evidence supports the role of menthol, a TRPM8 agonist, in enhanced energy expenditure, thermogenesis and BAT-like activity in classical WAT depots in a TRPM8 dependent and independent manner. The present study was designed to analyse whether oral and topical administration of menthol is bioavailable at subcutaneous adipose tissue and is sufficient to directlyinduce desired energy expenditure effects. GC-FID was performed to study menthol bioavailability in serum and subcutaneous white adipose tissue following oral and topical administration. Further, 3T3L1 adipocytes were treated with bioavailable menthol doses and different parameters (lipid accumulation, "browning/brite" and energy expenditure gene expression, metal analysis, mitochondrial complex's gene expression) were studied. No difference was observed in serum levels but significant difference was seen in the menthol concentration on subcutaneous adipose tissues after oral and topical application. Menthol administration at bioavailable doses significantly increased "browning/brite" and energy expenditure phenotype, enhanced mitochondrial activity related gene expression, increased metal concentration during adipogenesis but did not alter the lipid accumulation as well as acute experiments were performed with lower dose of menthol on mature adipocytes In conclusion, the present study provides evidence that bioavailable menthol after single oral and topical administration is sufficient to induce "brite" phenotype in subcutaneous adipose tissue However, critical dose characterization for its clinical utility is required.

Pharmacokinetics behaviors of l-menthol after inhalation and intravenous injection in rats and its inhibition effects on CYP450 enzymes in rat liver microsomes.

1. l-Menthol, as a kind of monocyclic terpene, is widely used in inhalation formulations, food and tobacco. The purpose of this study was to investigate the pharmacokinetic behavior of l-menthol as well as its influence on the activities of cytochrome P450 enzymes. 2. The pharmacokinetic behaviors of l-menthol after inhalation (50 mg/kg) and intravenous injection (10 mg/kg) were investigated. A rat liver microsomal model was adopted to elucidate the inhibitory effect of l-menthol on CYP1A2, CYP2C11, CYP2D1/2, CYP2D4, CYP2E1 and CYP3A1 using phenacetin, tolbutamide, omeprazole, dextromethorphan, chlorzoxazone and testosterone as probe drugs, respectively. 3. The plasma concentration reached the Cmax within 1.0 h (inhalation) and descended with the T1/2 of 8.53 and 6.69 h for inhalation and i.v. administration, respectively. IC50 for inhibition of l-menthol on CYP 450 enzymes were 4.35 µM for 2D4, 8.67 µM for 1A2, 13.02 µM for 3A1, 14.78 µM for 2D1/2, 234.9 µM for 2C11 and 525.4 µM for 2E1, respectively. 4. The results illustrate the pharmacokinetic process of l-menthol in rats and provide information for further rational applications. l-Menthol had moderate inhibitions on CYP2D4 and 1A2, which might affect the disposition of medicines primarily dependent on these pathways.

A Novel Ileocolonic Release Peppermint Oil Capsule for Treatment of Irritable Bowel Syndrome: A Phase I Study in Healthy Volunteers.

INTRODUCTION: Peppermint oil (PO) has been shown to reduce abdominal pain in patients with irritable bowel syndrome (IBS). PO is assumed to induce intestinal smooth muscle relaxation and desensitization of nociceptive nerve afferents. To increase colonic PO concentration, an ileocolonic release peppermint oil (IC-PO) capsule has been developed. The aim of this study was to compare pharmacokinetic parameters of the currently available small intestinal release PO (SI-PO) and the novel IC-PO. METHODS: In this randomized, double-blind, crossover study, subjects received 182 mg of either SI-PO or IC-PO in a crossover design with a washout period of more than 14 days. Blood samples were collected to determine menthol glucuronide concentrations. RESULTS: Eight healthy volunteers (50% female, median age 22) were included. The time to reach the maximum concentration (Tmax) of IC-PO was significantly longer compared to SI-PO with a median (IQR) of 360 (360-405) versus 180 (120-180) min. The lag time (Tlag) was significantly longer with a median (IQR) of 225 (204-284) for IC-PO compared to 37 (6-65) min for SI-PO. The areas under the menthol glucuronide plasma concentration-time curves were significantly smaller with a median (IQR) of 2331 µg h/L (2006-2510) for IC-PO compared to 2623 µg h/L (2471-2920) for SI-PO. No significant differences were found in peak concentrations and elimination half-lives. CONCLUSION: IC-PO has a significantly delayed peak menthol glucuronide concentration and Tlag, both pointing to the release of PO in the more distal part of the intestine. This may enhance therapeutic efficacy as it results in increased exposure of colonic mucosal afferents to the PO. A randomized controlled trial investigating the efficacy of SI and IC-PO in IBS is currently ongoing. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT02291445, EudraCT database 2014-004195-32.

Formulation Optimization and In-vitro and In-vivo Evaluation of Lornoxicam Ethosomal Gels with Penetration Enhancers.

BACKGROUND: Ethosomes, a novel type of percutaneous drug delivery carrier with a lipid bilayer structure, penetrate the skin barrier due to their deformability and malleability, and presence of ethanol that fluidizes lipids in the skin. In order to further enhance the delivery of drugs through the skin, penetration enhancers are widely used. OBJECTIVE: The objective of this work was to develop an optimized formulation of lornoxicam ethosomal gels, investigate skin permeability with the addition of penetration enhancers, and evaluate the invivo pharmacodynamics of these formulations. METHODS: Lornoxicam ethosomes were prepared by the ethanol injection method and optimized using the orthogonal design method. Lornoxicam ethosomal gels with enhancers were prepared and optimized using in-vitro transdermal delivery experiments. Experiments on lornoxicam ethosomal gels containing various enhancers such as azone, menthol, lauryl alcohol, and oleic acid were conducted using vertical Franz diffusion cells to measure the percutaneous permeability of the different formulations. Furthermore, the in-vivo analgesic effects of the optimized lornoxicam ethosomal gels were examined using the hot-plate and acetic acid-induced writhing tests. Anti-inflammatory activity was investigated using the dimethylbenzene-induced mouse ear swelling method. RESULTS: The results showed that compared to other formulations, the optimized lornoxicam ethosomal gels with 5 % menthol significantly increased transdermal penetration. Meanwhile, the optimized lornoxicam ethosomal gels showed remarkably anti-nociceptive and anti-inflammatory activity compared with the plain lornoxicam gels. CONCLUSION: These results suggest that the optimized ethosomal gel formulated in this study is a promising lornoxicam carrier in transdermal delivery systems to enhance anti-nociceptive and antiinflammatory efficiency.

Diclofenac systemic bioavailability of a topical 1% diclofenac + 3% menthol combination gel vs. an oral diclofenac tablet in healthy volunteers: a randomized, open-label, crossover study
.

OBJECTIVE: Evaluate systemic exposure with repeated topical application of a fixed-combination topical gel product containing 1% diclofenac sodium and 3% menthol in either of 2 formulation packages relative to oral administration. METHODS: In this phase 1, single-center, 4-way crossover study, healthy volunteers aged 18 - 50 years underwent consecutive 3-day treatment regimens in a randomly assigned sequence with each of 4 treatment groups: 4 g of topical 1% diclofenac + 3% menthol gel administered via an aluminum tube or roll-on device applied 4 times daily; 4 g of topical 1% diclofenac sodium gel (Voltaren Gel) applied 4 times daily; and oral diclofenac sodium tablets 50 mg 3 times daily. Treatment regimens were separated by 2-day washout periods. RESULTS: A total of 18 subjects enrolled and completed the study. Relative to oral administration, area under the concentration time curve from 48 to 72 hours (AUC48-72) with topical administration of 1% diclofenac + 3% menthol gel from a tube or roll-on device was 16.1% (90% CI: 12.2 - 21.1%) and 14.4% (90% CI: 11.0 - 19.0%), respectively. The diclofenac/menthol combination delivered significantly higher exposures of diclofenac compared with Voltaren Gel. A higher number of adverse events (AEs) occurred with the topical diclofenac/menthol combination (61%) vs. Voltaren Gel (22%) or oral diclofenac (6%); most were local skin reactions. No difference in systemic AEs was observed among the groups. CONCLUSION: As expected, systemic exposure was significantly lower with the topical diclofenac/menthol treatment regimens compared with oral diclofenac. Local skin AEs were increased with the topical combination product, but the risk of systemic AEs was low.
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Microemulsions based on paeonol-menthol eutectic mixture for enhanced transdermal delivery: formulation development and in vitro evaluation.

In this work, microemulsion-based gels were prepared for transdermal delivery of paeonol. Microemulsions containing eutectic mixtures of paeonol and menthol were developed. The obtained microemulsions were evaluated for particle size, viscosity and physical stability. The selected microemulsions were incorporated into Carbopol gels. Drug crystallization behavior during a short-term storage was compared and in vitro permeation and deposition study were conducted on mouse skin. Results showed that the eutectic liquids of paeonol and menthol at all ratio (6:4, 5:5 and 4:6) could form microemulsions but with significantly different physical characteristics. As the ratio of paeonol increased, the prepared microemulsions exhibited larger droplet size, higher viscosity and quicker crystal growth. Microemulsion containing paeonol and menthol at a ratio of 4:6 possessed the smallest size of 27 nm. Accordingly, the related gel showed better physical stability during 10 days of storage, as well as the highest percent of drug deposition (111.8 µg/cm2) and steady-state flux (0.3 µg/cm2 h). These results suggested that the microemulsion formulation is a preferable approach for enhanced skin permeation, and the microemulsion based on drug-menthol eutectic mixture might be used as a potential transdermal delivery system for better therapeutic efficacy.

A survey of subcutaneous blood flow in patients with SMID and subcutaneous ceftazidime administration using mentholated warm compresses in healthy subjects.

OBJECTIVES: To investigate subcutaneous blood flow rate (SBFR) in healthy volunteers and patients with severe motor and intellectual disabilities (SMID), and evaluate the effect of mentholated warm compresses (MWCs) on SBFR and subcutaneous ceftazidime absorption in healthy volunteers. METHODS: SBFR at the forearm, chest and abdomen were evaluated in Japanese healthy volunteers and in adults with SMID. The effects of MWCs on blood flow rate and ceftazidime pharmacokinetics were evaluated in healthy volunteers. RESULTS: SBFR was significantly lower in the forearms of female patients with SMID (n = 11) than in the forearms of healthy females (n = 6); it was not significantly lower in the abdomen or chest. There were no significant differences between male patients (n = 18) or controls (n = 12) in SBFR at any site. MWC application increased SBFR 1.3- to 2.0-fold compared with baseline in healthy controls (n = 6). MWC application increased ceftazidime maximum blood concentration, SBFR and time above mutant prevention concentration in a single healthy subject. CONCLUSIONS: Abdominal SBFR in patients with SMID did not differ from that of healthy subjects. MWC application increases SBFR and subcutaneous drug absorption rate in healthy humans.

The absorption and metabolism of a single L-menthol oral versus skin administration: Effects on thermogenesis and metabolic rate.

We investigated the absorption and metabolism pharmacokinetics of a single L-menthol oral versus skin administration and the effects on human thermogenesis and metabolic rate. Twenty healthy adults were randomly distributed into oral (capsule) and skin (gel) groups and treated with 10 mg kg(-1) L-menthol (ORALMENT; SKINMENT) or control (lactose capsule: ORALCON; water application: SKINCON) in a random order on two different days. Levels of serum L-menthol increased similarly in ORALMENT and SKINMENT (p > 0.05). L-menthol glucuronidation was greater in ORALMENT than SKINMENT (p < 0.05). Cutaneous vasoconstriction, rectal temperature and body heat storage showed greater increase following SKINMENT compared to ORALMENT and control conditions (p < 0.05). Metabolic rate increased from baseline by 18% in SKINMENT and 10% in ORALMENT and respiratory exchange ratio decreased more in ORALMENT (5.4%) than SKINMENT (4.8%) compared to control conditions (p < 0.05). Levels of plasma adiponectin and leptin as well as heart rate variability were similar to control following either treatment (p > 0.05). Participants reported no cold, shivering, discomfort, stress or skin irritation. We conclude that a single L-menthol skin administration increased thermogenesis and metabolic rate in humans. These effects are minor following L-menthol oral administration probably due to faster glucuronidation and greater blood menthol glucuronide levels.

Novel perspectives in the tuberculosis treatment: Administration of isoniazid through the skin.

Despite its high efficacy in anti-tuberculosis therapy, the oral administration of isoniazid (INH) may lead to poor patient compliance due to hepatotoxicity events. In this context, the transdermal administration of INH was evaluated, for the first time, since this route avoids hepatic first pass effect. INH was applied to porcine skin in Franz diffusion chambers alone and with 5% menthol, limonene or Transcutol(®). Infrared and DSC analyses were selected for mechanistic studies. The transdermal absorption of INH was sufficient to ensure a systemic therapeutic effect. Menthol was not able to improve the absorption of INH, but it increased the drug accumulation in skin compared to the control (1.4-fold). Transcutol(®) reduced permeation flux of INH (2.2-fold) and also increased the amount of drug retained in skin (1.7-fold). Limonene was the most effective excipient since it increased permeation flux of INH (1.5-fold) and lag time was greatly shortened (2.8-fold). DSC and FTIR analyses of limonene-treated skin suggest higher degree of disorder in lipid bilayers. Transdermal delivery of INH was positively correlated with logP of chemical enhancers. INH can be efficiently delivered by skin route and specific excipients may be selected depending on intended use.

[Study on pharmacokinetics and in vitro/in vivo correlation of menthol in Zhike Chuanbei Pipa dropping pills in rats].

To determine the concentration of menthol in rat plasma by GC. Rats were administered with single dose of Zhike Chuanbei Pipa dropping pills (ZCPDP) and different doses of menthol herbs. DAS 3. 1.6 software was used to calculate pharmacokinetic parameters, and the accumulative absorption percentage of menthol was calculated by Loo-Riegelman method. The linear regression analysis was made in vitro/in vivo accumulative absorption percentages to detect the in vitro/in vivo correlation. The results of the study showed that the pharmacokinetics behavior of menthol in ZCPDP was in conformity with two-compartment model characteristics. The main parameters were: tmax was 10 min, t1/2beta was (183. 93 52. 75) min, CL/F was (0. 426 +/- 0. 194) L . min-1 . kg-1, all of which were no difference between ZCPDP and menthol herbs with the same dosage. There were significant differences in tmax, t1/2beta, CL/F between menthol herbs with different dosages (P <0. 05) , with indirect proportion between AUC0-infinity and dosage. The regression equation of ZCPDP's accumulative absorption percentage and accumulative release percentage was Fa = 1. 160 3Q - 19. 968, r = 0. 981 3. These results suggested that the pharmacokinetics behavior was similar between ZCPDP and menthol herbs with the same dosage in rats, with good in vitro/in vivo correlation. There were significant differences in pharmacokinetics of menthol in the range of 19.2-570 mg . kg-1.

Plasma and dermal pharmacokinetics of terpinen-4-ol in rats following intravenous administration.

Terpinen-4-ol, a naturally occurring monoterpene, has been shown to possess antibacterial, antioxidant and anti-inflammatory activities. Furthermore, recent reports have demonstrated that terpinen-4-ol could be developed as new therapies against melanoma either in systemic administration or targeted drug delivery. The purpose of this study was to investigate the pharmacokinetics of terpinen-4-ol in rat plasma and dermal tissue following intravenous (i.v.) bolus injection of terpinen-4-ol at a dose of 2 mg/kg. Unbound concentrations of terpinen-4-ol in dermis were continuously determined by dermal microdialysis. Simultaneously, a conventional blood sampling was performed. The concentrations of terpinen-4-ol in plasma and microdialysates were determined by validated gas chromatography-mass spectrometry. Following i.v. bolus administration, terpinen-4-ol rapidly distributed into the dermis and reached relatively low levels with an average maximum concentration (Cmax) of 0.10 +/- 0.06 microg/ml in comparison with a plasma Cmax of 6.30 +/- 1.90 microg/ml. The free terpinen-4-ol concentrations in dermal tissue were lower than the corresponding total and free plasma concentrations for the entire length of study, indicating that plasma levels do not provide information of actual terpinen-4-ol concentrations in the skin. This study demonstrates that dermal microdialysis is an effective and minimally invasive tool to evaluate the dermal pharmacokinetics of terpinen-4-ol following systemic administration.

Central mechanisms of menthol-induced analgesia.

Menthol is one of the most commonly used chemicals in our daily life, not only because of its fresh flavor and cooling feeling but also because of its medical benefit. Previous studies have suggested that menthol produces analgesic action in acute and neuropathic pain through peripheral mechanisms. However, the central actions and mechanisms of menthol remain unclear. Here, we report that menthol has direct effects on the spinal cord. Menthol decreased both ipsilateral and contralateral pain hypersensitivity induced by complete Freund's adjuvant in a dose-dependent manner. Menthol also reduced both first and second phases of formalin-induced spontaneous nocifensive behavior. We then identified the potential central mechanisms underlying the analgesic effect of menthol. In cultured dorsal horn neurons, menthol induced inward and outward currents in a dose-dependent manner. The menthol-activated current was mediated by Cl(-) and blocked by bicuculline, suggesting that menthol activates γ-aminobutyric acid type A receptors. In addition, menthol blocked voltage-gated sodium channels and voltage-gated calcium channels in a voltage-, state-, and use-dependent manner. Furthermore, menthol reduced repetitive firing and action potential amplitude, decreased neuronal excitability, and blocked spontaneous synaptic transmission of cultured superficial dorsal horn neurons. Liquid chromatography/tandem mass spectrometry analysis of brain menthol levels indicated that menthol was rapidly concentrated in the brain when administered systemically. Our results indicate that menthol produces its central analgesic action on inflammatory pain probably via the blockage of voltage-gated Na(+) and Ca(2+) channels. These data provide molecular and cellular mechanisms by which menthol decreases neuronal excitability, therefore contributing to menthol-induced central analgesia.

Menthol attenuates respiratory irritation responses to multiple cigarette smoke irritants.

Menthol, the cooling agent in peppermint, is added to almost all commercially available cigarettes. Menthol stimulates olfactory sensations, and interacts with transient receptor potential melastatin 8 (TRPM8) ion channels in cold-sensitive sensory neurons, and transient receptor potential ankyrin 1 (TRPA1), an irritant-sensing channel. It is highly controversial whether menthol in cigarette smoke exerts pharmacological actions affecting smoking behavior. Using plethysmography, we investigated the effects of menthol on the respiratory sensory irritation response in mice elicited by smoke irritants (acrolein, acetic acid, and cyclohexanone). Menthol, at a concentration (16 ppm) lower than in smoke of mentholated cigarettes, immediately abolished the irritation response to acrolein, an agonist of TRPA1, as did eucalyptol (460 ppm), another TRPM8 agonist. Menthol's effects were reversed by a TRPM8 antagonist, AMTB. Menthol's effects were not specific to acrolein, as menthol also attenuated irritation responses to acetic acid, and cyclohexanone, an agonist of the capsaicin receptor, TRPV1. Menthol was efficiently absorbed in the respiratory tract, reaching local concentrations sufficient for activation of sensory TRP channels. These experiments demonstrate that menthol and eucalyptol, through activation of TRPM8, act as potent counterirritants against a broad spectrum of smoke constituents. Through suppression of respiratory irritation, menthol may facilitate smoke inhalation and promote nicotine addiction and smoking-related morbidities.

A phase I study evaluating tolerability, pharmacokinetics, and preliminary efficacy of L-menthol in upper gastrointestinal endoscopy.

Peppermint oil has been shown to relax gastrointestinal smooth muscle. In this randomized, placebo-controlled study, an L-menthol preparation, NPO-11, was assessed for tolerability and pharmacokinetics (PK) during gastrointestinal endoscopy. Single doses of NPO-11, as high as 320 mg, were well tolerated. NPO-11 was rapidly absorbed, with peak concentrations reached within 1 h after administration. Approximately 70% of the administered L-menthol and its metabolites were excreted in the urine, and this amount fluctuated with no change in the dose. The principal metabolite identified in plasma and urine was menthol glucuronide. The other metabolites include mono- or di-hydroxylated menthol derivatives, most of which are excreted, in part, as glucuronic acid conjugates. The pharmacokinetic data indicated that when NPO-11 is sprayed directly onto the gastric mucosa, it is rapidly metabolized to glucuronic acid conjugates that are excreted in urine. The findings from this study provide new data on the safety and PK of NPO-11 and support further trials.

Pharmacokinetic study of borneol and menthol in rats after oral administration of qingyan drop pills.

Both borneol and menthol are bioactive substances derived from Chinese herbal medicines. In order to understand the pharmacokinetics of borneol and menthol in Qingyan drop pills, a rapid, sensitive, and simple gas chromatographic (GC) method with flame ionization detection (FID) was developed for the simultaneous determination of borneol and menthol in rat plasma. Sample preparations were carried out by liquid-liquid extraction (LLE) with an internal standard solution of naphthalene. The analytes and internal standard (IS, naphthalene) were separated well on an HP-1 capillary column. The pharmacokinetic parameters were estimated by a compartmental method using the Phoenix WinNonlin software program (Version 6.0). The standard curves were linear over a wide concentration range of 2.5-50.0 ng/µL ( R = 0.9963), 8.7-62.2 ng/µL ( R = 0.9994) for both borneol and menthol in plasma, respectively. The limits of quantification (LOQ) of borneol and menthol in plasma were 2.4 ng/µL and 5.0 ng/µL, respectively. The intra-day precisions for borneol and menthol were < or = 10.0 % R. S. D. at the LOQ and < or = 6.0 % at higher concentrations. The average value of CMAX was 18.97 ± 2.71 ng/µL with a TMAX at 20.00 ± 0.00 min for borneol after oral administration of the drop pills; for menthol, the average value of CMAX was 79.02 ± 11.40 ng/µL with a TMAX at 25.00 ± 4.40 min. This validated assay method was successfully applied to a pharmacokinetic study of borneol and menthol after oral administration of Qingyan drop pills in rat. The results showed that the kinetics of borneol and menthol can be described by an open one-compartment model. The pharmacokinetic parameters provide some information for clinical administration of Qingyan drop pills.

Bioequivalence evaluation of menthol after oral administration of peppermint oil soft capsules in dogs.

A randomized, two-way, crossover, bioequivalence study in 6 beagle dogs was conducted to compare the bioavailability of two peppermint oil formulations, soft capsule and hard capsule. The drug was given in a single dose of two capsules (total, 200 mg), and blood samples were withdrawn during the 12 h after drug administration. Menthol (CAS 2216-51-5) as the main component of peppermint oil was determined by a gas chromatography-tandem mass spectrometry (GC-MS/I MS) method after cleavage with beta-glucuronidase. The following pharmacokinetic variables were computed for the two formulations: maximum concentration (Cmax), time to maximum concentration (Tmax), half-life of elimination (t1/2), mean residence time (MRT), and areas under the plasma concentration-time curve (AUC(0-t) and AUC(0-infinity)). For calculation of the 90% confidence interval (CI), an analysis of variance (ANOVA) was carried out. The results indicated that treatment and subject had statistically significant effect on AUC(0-t), AUC(0-infinity), and Cmax, and the 90% CIs for AUC(0-t), AUC(0-infinity), and Cmax were outside the acceptable bioequivalence range. The relative bioavailability was 121.4 +/- 10.6% for AUC(0-infinity). Therefore, it can be concluded that the two formulations are not bioequivalent and the bioavailability of soft capsules is significantly higher than that of hard capsules.