Menthol: a refreshing look at this ancient compound

Menthol is a naturally occurring cyclic terpene alcohol of plant origin, which has been used since antiquity for medicinal purposes. Its use in dermatology is ubiquitous, where it is frequently part of topical antipruritic, antiseptic, analgesic, and cooling formulations. Despite its widespread use, it was only recently that the mechanism by which menthol elicits the same cool sensation as low temperature was elucidated upon, with the discovery of the TRPM8 receptor. Although almost 5 years have passed since the discovery of this receptor, many dermatologists are still unaware of menthol's underlying target. The purpose of this review is to highlight the recent advances in the mechanism of action of menthol and to provide an overview of its dermatologic applications.

Effects of components of Artemisia annua on coccidia infections in chickens

Four experiments were run to test the anticoccidial activity of dried Artemisia annua leaves and several of their chemical constituents for possible use as prophylactic feed additives. When fed over a period of 3 wk at a level of 5%, a dried leaf supplement of A. annua provided significant protection against lesions due to Eimeria tenella but not Eimeria acervulina or Eimeria maxima. When fed over a period of 5 wk at a level of 1% to chicks undergoing immunization with a live vaccine, it provided significant protection in partially immunized chicks against E. acervulina and E. tenella lesions from a dual species challenge infection. It also afforded lower mean lesion scores in challenged chicks immunized over a period of 5 wk. Artemisinin, an antimalarial component of A. annua, was present at a level of 0.034% in the dried leaf preparation. A 5% supplement thus afforded about 17 ppm artemisin. When the pure compound was fed at that level for a period of 3 wk, it protected weight gains and significantly reduced lesion scores attributable to E. tenella but not E. acervulina. Other components of A. annua, camphor and 1,8-cineole, at 119 ppm also protected weight gains, and reduced E. tenella lesion scores. Camphor reduced E. acervulina lesions. Artemisinin fed for 4 wk at levels of 2, 8.5, and 17 ppm significantly reduced oocyst output from separate E. acervulina and E. tenella infections and a dual species infection. Pure artemisinin thus appears to be effective against at least two coccidia species when used as a feed additive, and its activity may depend, in part, on the length of time it is administered before a challenge infection.

Effect of topically applied menthol on thermal, pain and itch sensations and biophysical properties of the skin

The effect of menthol and alcohol as its vehicle on thermal sensations, pain, experimental itch and irritation were studied in 18 subjects, using a computerized thermal sensory analyzer, laser Doppler flowmetry and an evaporimeter for transepidermal water loss (TEWL). Menthol had a subjective cooling effect lasting up to 70 min in 12/18 subjects; however, it did not affect cold and heat threshold, nor did it affect cold and heat pain threshold. Alcohol produced an immediate cold sensation lasting up to 5 min in 4/18 subjects and lowered the sensitivity of cold sensation threshold (P < 0.05). Histamine injection did not change thermal and pain thresholds. Menthol did not alleviate histamine-induced itch magnitude, nor its duration. Following histamine injection, cold sensation median threshold decreased by 1.2 degrees C from (29.9 degrees C to 28.7 degrees C) on the site treated with menthol (P < 0.01) with similar changes in thresholds at the alcohol-treated site (P < 0.05). Warm sensation and pain threshold in subjects receiving histamine injections, measured after menthol and alcohol application, did not differ from their baseline values with histamine alone. TEWL at the site treated with menthol was significantly higher (P < 0.05) than at the alcohol-treated and the control site (P < 0.01), suggesting that menthol has a higher skin irritating effect, or at least alters the stratum corneum water permeability. Our results suggest that menthol fulfills the definition of a counterirritant, but does not affect histamine-induced itch, nor does it affect pain sensation.

Therapy of pruritus

IMPORTANCE OF THE FIELD

Pruritus is the predominant symptom of skin disease. Owing to the poorly understood pathophysiology, the development of effective treatment modalities for pruritus has proven to be particularly difficult. At present, there is no universally accepted therapy for itch. The purpose of this review is to provide an update on the treatment of pruritus.

AREAS COVERED IN THIS REVIEW

An overview of current, emerging and possible future therapies for pruritus is provided.

WHAT THE READER WILL GAIN

Insights into possible treatment regimes for pruritus in different clinical scenarios.

TAKE HOME MESSAGE

The therapy of pruritus is challenging and at present takes on an individualistic approach. Recent advancements in the mechanisms that underlie this distressing symptom have identified new targets for future therapy.

1,8-cineol, a food flavoring agent, prevents ethanol-induced gastric injury in rats

This study investigated the gastroptrotective effect of 1,8-cineole (cineole) on ethanol-induced gastric mucosal damage in rats and the possible mechanisms involved. 1,8-Cineole (50-200 mg/kg), given orally 1 hr before administration of 1 ml of absolute ethanol significantly attenuated the ethanol-induced gastric injury in a manner similar to nordihydroguairetic acid, a known lipoxygenase inhibitor. 1,8-Cineole showed a tendency to restore the ethanol-associated decreases in nonprotein sulfhydryls, suggesting a possible antioxidant effect. In gastric secretion studies, 1,8-cineole, similar to cimetidine, a known histamine-2 receptor antagonist, demonstrated significant inhibitions of both gastric juice volume as well as total acid output. The protection offered by 1,8-cineole was found to be unaltered by 8-phenyltheophylline or L-NAME, indicating that its effect is not mediated by endogenous adenosine or nitric oxide. These results, taken together with the earlier reports, suggest that the antioxidant and lipoxygenase inhibitory actions of 1,8-cineole are of prime importance in affording gastroprotection against ethanol injury in the rat.

Effects of Menthol on Nicotine Pharmacokinetic, Pharmacology and Dependence in Mice

Although menthol, a common flavoring additive to cigarettes, has been found to impact the addictive properties of nicotine cigarettes in smokers little is known about its pharmacological and molecular actions in the brain. Studies were undertaken to examine whether the systemic administration of menthol would modulate nicotine pharmacokinetics, acute pharmacological effects (antinociception and hypothermia) and withdrawal in male ICR mice. In addition, we examined changes in the brain levels of nicotinic receptors of rodents exposed to nicotine and menthol. Administration of i.p. menthol significantly decreased nicotine’s clearance (2-fold decrease) and increased its AUC compared to i.p. vehicle treatment. In addition, menthol pretreatment prolonged the duration of nicotine-induced antinociception and hypothermia (2.5 mg/kg, s.c.) for periods up to 180 min post-nicotine administration. Repeated administration of menthol with nicotine increased the intensity of mecamylamine-precipitated withdrawal signs in mice exposed chronically to nicotine. The potentiation of withdrawal intensity by menthol was accompanied by a significant increase in nicotine plasma levels in these mice. Western blot analyses of α4 and β2 nAChR subunit expression suggests that chronic menthol impacts the levels and distribution of these nicotinic subunits in various brain regions. In particular, co-administration of menthol and nicotine appears to promote significant increase in β2 and α4 nAChR subunit expression in the hippocampus, prefrontal cortex and striatum of mice. Surprisingly, chronic injections of menthol alone to mice caused an upregulation of β2 and α4 nAChR subunit levels in these brain regions. Because the addition of menthol to tobacco products has been suggested to augment their addictive potential, the current findings reveal several new pharmacological molecular adaptations that may contribute to its unique addictive profile.

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: effects on nasal sensation of airflow and the drive to breathe

Menthol, in lozenges, nasal sprays, vapo-rubs, inhalers, and cough syrups, is widely used as a treatment for rhinitis that is associated with acute upper respiratory tract infection and allergy. Menthol as a plant extract has been used in traditional medicine in Asia for the treatment of respiratory diseases for hundreds of years, but it was only introduced to the West as a medicine at the end of the 19th century. With the recent discovery of a menthol receptor on the sensory nerves that modulate the cool sensation, menthol has graduated from the realms of herbal medicine into the field of molecular pharmacology. This review concerns the physiologic and pharmacologic mechanisms that underlie the widespread use of menthol as a treatment for the relief of nasal congestion associated with rhinitis and its effects on the drive to breathe and symptomatic relief of dyspnea.

Antimicrobial strategies in the prevention of dental caries

Antimicrobial agents, applied either professionally or delivered from dentifrices or mouthwashes, could reduce caries by controlling plaque formation, suppressing cariogenic species, or by inhibiting bacterial metabolism. Chlorhexidine has proven anticaries activity; other agents might also prevent caries by means of their antiplaque properties. Sugar substitutes stabilize the microflora by reducing the number of acid challenges to plaque and stimulating saliva flow; some also have antimicrobial properties, especially against mutans streptococci. Vaccines have been prepared from purified antigens of mutans streptococci. These vaccines confer protection in non-human primates, but have yet to be tested in a human clinical trial.

Effect of aromatics on lung mucociliary clearance in patients with chronic airways obstruction

BACKGROUND

Complementary and alternative medicine have become an increasingly topical theme in respiratory medicine. Aromatics are a commonly used ingredient in a number of proprietary medicines. It is well established that lung mucus clearance is impaired in patients with chronic airways obstruction. This study investigated whether aromatics delivered by inunction could be objectively shown to enhance lung clearance.

METHODS

We studied 12 patients with chronic bronchitic with a mean standard error (SE) age of 67 (2) years (mean [SE] tobacco consumption history of 64 [12] pack-years). We used a randomized, single-blinded, placebo-controlled crossover trial within patient design assessing the effect of 7.5 g of aromatics inunction (compared to a "no-treatment baseline" and to a petrolatum "placebo") on lung mucus clearance measured by a standard radioaerosol technique.

RESULTS

Aromatic treatment significantly enhanced clearance at two time points 30 (p < 0.05) and 60 (p < 0.02) minutes postradioaerosol inhalation but had no demonstrable further effect over the following 5 hours despite further application of the inunction. The clearance improvement (relative to a baseline) observed during the first hour of testing was significantly correlated (p < 0.01) with the concentration level of aromatics.

CONCLUSION

Our data, thus, provide objective evidence of a positive effect of aromatics inunction on mucus clearance in chronic airways obstruction.

Menthol-beta-D-glucuronide: a potential prodrug for treatment of the irritable bowel syndrome

Menthol-beta-D-glucuronide is a potential prodrug for colonic delivery of the spasmolytic agent menthol. Menthol is the primary constituent of peppermint oil, which is used to treat the irritable bowel syndrome. The chemical stability of menthol-beta-D-glucuronide was assessed at various pHs (1.5, 4.5, 6.0 and 7.4) over a 4 to 24 h period at 37 degrees C. The prodrug was stable, i.e., there was less than 0.1% hydrolysis of the prodrug, at pHs of 4.5, 6.0 and 7.4. At pH 1.5, the prodrug was about 20% hydrolyzed over a 4 h period suggesting the need for an enteric coating to prevent premature hydrolysis in the stomach. The stability of the prodrug was also assessed in luminal contents of the laboratory rat and in human stool samples. These studies were performed at concentrations designed to assess relative velocities of hydrolysis (i.e., substrate concentrations in excess of the Km). The prodrug was stable in luminal contents of the rat stomach, proximal small intestine, and the distal small intestine. The rate of hydrolysis of menthol-beta-D-glucuronide was 6.26 +/- 2.88 nmol min-1 mg-1 and 2.34 +/- 1.22 nmol min-1 mg-1 in luminal contents of the rat cecum and colon, respectively. The hydrolysis rate of menthol-beta-D-glucuronide was lower in human stool samples (0.52 +/- 0.46 nmol min-1 mg-1). The prodrug had a measured log octanol/buffer partition coefficient of -1.61 suggesting it should be poorly absorbed from the lumen of the gastrointestinal tract. The data support the hypothesis that menthol-beta-D-glucuronide is a candidate for the delivery of menthol to the large intestine under in vivo conditions.

Transdermal delivery system for zidovudine:in vitro, ex vivo andin vivo evaluation

The objective of this study was to prepare a transdermal delivery system (TDS) for zidovudine (AZT) with a combination of menthol and oleic acid as penetration enhancers incorporated in hydroxypropyl methylcellulose, and to evaluate ex vivo as well as in vivo permeation across rat skin. It was found that AZT in gel formulation was stable in both refrigerated as well as accelerated stability conditions for 3 months and further, the gel did not significantly retard the permeability of AZT across the skin in comparison with solution formulation. Ex vivo steady state flux of AZT across rat skin from gel was 2.26 mg cm(-2) h(-1), which is sufficient to achieve therapeutic plasma concentrations. Intravenous pharmacokinetic parameters of AZT in rats were determined and used together with ex vivo flux data to generate theoretical plasma profiles of AZT and compared with plasma concentrations achieved after application of TDS. Further, steady state plasma concentrations of drug following multiple applications of TDS were determined and good correlations between ex vivo and in vivo data were observed. In addition, the combination of penetration enhancers used at 2.5% w/w in this study proved efficient in achieving sufficient enhancement in the transdermal permeability of AZT across rat skin with reduced skin irritation potential when compared with individual penetration enhancers at higher concentrations.

Rococo study: a real-world evaluation of an over-the-counter medicine in acute cough (a multicentre, randomised, controlled study)

OBJECTIVES

To investigate the efficacy and safety of CS1002, an over-the-counter cough treatment containing diphenhydramine, ammonium chloride and levomenthol in a cocoa-based demulcent.

DESIGN

A multicentre, randomised, parallel group, controlled, single-blinded study in participants with acute upper respiratory tract infection-associated cough.

SETTING

4 general practitioner (GP) surgeries and 14 pharmacies in the UK.

PARTICIPANTS

Participants aged ≥18 years who self-referred to a GP or pharmacist with acute cough of <7 days' duration. Participant inclusion criterion was cough severity ≥60 mm on a 0-100 mm visual analogue scale (VAS). Exclusion criteria included current smokers or history of smoking within the past 12 months (including e-cigarettes). 163 participants were randomised to the study (mean participant age 38 years, 57% females).

INTERVENTIONS

Participants were randomised to CS1002 (Unicough) or simple linctus (SL), a widely used cough treatment, and treatment duration was 7 days or until resolution of cough.

MAIN OUTCOME MEASURES

The primary analysis was intention-to-treat (157 participants) and comprised cough severity assessed using a VAS after 3 days' treatment (prespecified primary end point at day 4). Cough frequency, sleep disruption, health status (Leicester Cough Questionnaire (LCQ-acute)) and cough resolution were also assessed.

RESULTS

At day 4 (primary end point), the adjusted mean difference (95% CI) in cough severity VAS between CS1002 and SL was -5.9 mm (-14.4 to 2.7), p=0.18. At the end of the study (day 7) the mean difference in cough severity VAS was -4.2 mm (-12.2 to 3.9), p=0.31. CS1002 was associated with a greater reduction in cough sleep disruption (mean difference -11.6 mm (-20.6 to 2.7), p=0.01) and cough frequency (mean difference -8.1 mm (-16.2 to 0.1), p=0.05) compared with SL. There was greater improvement in LCQ-acute quality of life scores with CS1002 compared with SL: mean difference (95% CI) 1.2 (0.05 to 2.36), p=0.04 after 5 days' treatment. More participants prematurely stopped treatment due to cough improvement in the CS1002 group (24.4%) compared with SL (10.7%; p=0.02). Adverse events (AEs) were comparable between CS1002 (20.5%) and SL (27.6%) and largely related to the study indication. 6 participants (7%) in the CS1002 group reduced the dose of medication due to drowsiness/tiredness, which subsequently resolved. These events were not reported by participants as AEs.

CONCLUSIONS

Although the primary end point was not achieved, CS1002 was associated with greater reductions in cough frequency, sleep disruption and improved health status compared with SL.

TRIAL REGISTRATION NUMBER

EudraCT number 2014-004255-31.

Dissolution of gall stones with an ursodeoxycholic acid menthol preparation: a controlled prospective double blind trial

In a controlled prospective double blind trial patients with cholesterol gall bladder stones are treated with ursodeoxy-cholic acid (group A: UDCA 11.1 mg/kg per day; n = 16) and Ursomenth respectively (group B: a mixture of UDCA/menthol: 4.75 mg/kg per day each; n = 17). With same stone number and size (10-12 mm) there is a complete dissolution rate in group A of 38%, and of 53% in group B within 15-16.9 months. The response rate (complete + partial dissolution) amounted to 75% and 76% respectively. In group A there is one case of stone calcification, in group B none. Both preparations are free of unwanted effects. This suggests that the cyclic monoterpene menthol enhances the effect of UDCA and is of comparable effect to a mixture of six different terpenes used in former times.

Targeting Chemosensory Ion Channels in Peripheral Swallowing-Related Regions for the Management of Oropharyngeal Dysphagia

Oropharyngeal dysphagia, or difficulty in swallowing, is a major health problem that can lead to serious complications, such as pulmonary aspiration, malnutrition, dehydration, and pneumonia. The current clinical management of oropharyngeal dysphagia mainly focuses on compensatory strategies and swallowing exercises/maneuvers; however, studies have suggested their limited effectiveness for recovering swallowing physiology and for promoting neuroplasticity in swallowing-related neuronal networks. Several new and innovative strategies based on neurostimulation in peripheral and cortical swallowing-related regions have been investigated, and appear promising for the management of oropharyngeal dysphagia. The peripheral chemical neurostimulation strategy is one of the innovative strategies, and targets chemosensory ion channels expressed in peripheral swallowing-related regions. A considerable number of animal and human studies, including randomized clinical trials in patients with oropharyngeal dysphagia, have reported improvements in the efficacy, safety, and physiology of swallowing using this strategy. There is also evidence that neuroplasticity is promoted in swallowing-related neuronal networks with this strategy. The targeting of chemosensory ion channels in peripheral swallowing-related regions may therefore be a promising pharmacological treatment strategy for the management of oropharyngeal dysphagia. In this review, we focus on this strategy, including its possible neurophysiological and molecular mechanisms.

Possible warfarin interaction with menthol cough drops

OBJECTIVE

To report a case of possible interaction of menthol cough drops (Halls) with warfarin in a patient awaiting cardioversion.

CASE SUMMARY

A 57-year-old white male awaiting cardioversion for atrial fibrillation was prescribed warfarin. His dosage was adjusted to 7 mg daily to provide stable international normalized ratio (INR) values of 2.28-2.68. Approximately one week later, his INR fell to 1.45. During a follow-up interview, the patient reported that he experienced a flu-like illness during the previous week and had been using menthol cough drops. No other potential causes for the decreased INR were found. Illness will most often elevate the INR; we therefore concluded that the cough drops were the likely cause of this reaction, and the warfarin dose was increased to 53 mg/wk. After discontinuing use of menthol cough drops, the warfarin dose was returned to the previous amount and the INR remained stabilized.

DISCUSSION

An objective causality assessment suggests that the decreased INR was possibly related to the use of menthol cough drops during warfarin therapy. The active ingredient in these cough drops is menthol. Menthol has been shown to affect the pharmacokinetics of other drugs by inducing or inhibiting cytochrome P450 isoenzymes and slowing drug absorption. It is not clear whether these mechanisms played a role in this case. As of January 5, 2005 this is the first case report documenting an interaction between warfarin and cough drops containing menthol.

CONCLUSIONS

This case documents a significant decrease in the INR following the use of menthol cough drops. Patients who are ill have several factors that can potentially affect their INR and should be monitored closely.

A study of a pre-brushing mouthrinse as an adjunct to oral hygiene

A previous clinical screening study demonstrated that a cetylpyridinium chloride (CPC) essential oil mouthrinse inhibited plaque regrowth to a significantly greater extent than a negative control or a triclosan/copolymer rinse when used without toothbrushing. The purpose of this study was to evaluate the same ingredient combination as a pre-brushing rinse over a 6-week period. The study employed a 4 group parallel design with a minimum of 50 subjects per group. Subjects with a minimum baseline plaque index of 1.95 were recruited. The formulations employed were two variations of a CPC/essential oil rinse, a triclosan/copolymer product, and a hydroalcohol negative control. Subjects were rendered plaque free at baseline and then rinsed twice daily before toothbrushing with their allocated product. Plaque was scored at 6 days and 6 weeks. Plaque scores were reduced at 6 days compared to baseline but there were no significant differences between any of the groups. At 6 weeks, plaque scores were significantly lower in both CPC/essential oil groups compared to control. Although both CPC/essential oil groups showed plaque scores which were lower than the triclosan group, in only one of the groups was the difference significant. The triclosan product was not significantly different from control. The results support the previous findings that a CPC/essential oil rinse could be a useful adjunct to oral hygiene when used prior to normal toothbrushing.

[Does the inhalation of a 1% L-menthol solution in the premedication of fiberoptic bronchoscopy affect coughing and the sensation of dyspnea?]

BACKGROUND

Inhalation of l-menthol inhibits cough and has been shown to reduce respiratory discomfort associated with loaded breathing. We investigated the effect of the inhalation of a 1% l-menthol solution in the premedication of fiberoptic bronchoscopy (FB) on the frequency of cough and the irritability of the tracheobronchial mucosa during FB in a blinded, randomized and placebo controlled study.

METHODS

64 pat. (30-78 yrs, 55 males) underwent routine FB. Premediction: atropine and hydrocodone s.c., inhalation of oxybuprocain by means of a jet nebulizer, sedation on demand. Verum-group: inhalation of 3 ml 1% l-menthol-solution. Placebo-group: 3 ml 0.05% l-menthol (to provide the typical smell). Before and after inhalation peak respiratory flow (PEF) was registered, during FB the frequency of cough was measured. The bronchoscopist scored the irritability of the tracheobronchial mucosa using a visual analog scale. The patients answered a questionnaire addressing their perception of dyspnea and cough on the day after FB compared to the day before.

RESULTS

The cough counts didn't show a significant difference between the groups. The irritability of the mucosa was increased in the verum group (main bronchus verum 62.2 +/- 22, placebo 48.6 +/- 23 [mm vissual analog scale, p = 0.03]). Cough and dyspnea reported by the patients decreased on the day after FB significantly compared to the day before (no difference between the groups). The inhalation of 1% l-menthol induced a significant increase of the PEF (verum 307 +/- 103 pre, 329 +/- 84 post [l/min, p = 0.003]) compared to placebo.

CONCLUSIONS

The inhalation of 1% l-menthol did not enhance the tolerability of the FB. However, l-menthol induced a significant increase of the PEF immediately after inhalation. Finally sensation of dyspnea was decreased in both groups at the day post FB.

Cold stimuli, hot topic: An updated review on the biological activity of menthol in relation to inflammation

BACKGROUND

Rising incidence of inflammation-related diseases is an increasing concern nowadays. However, while menthol is a wildly-used and efficacious complementary medicine, its pharmacological mechanism still remains uncertain. Superimposed upon that, the aim of this review is to summarize the contemporary evidence of menthol's anti-inflammatory activity.

METHODS

Using the pharmacopeias and electronic databases, including Web of Science, PubMed, and CNKI, this study analyzed the relevant research articles and review articles from 2002 to 2022 and concluded those results and conjectures to finish this article.

RESULTS

The decrease in pro-inflammatory cytokines and related inflammatory markers, as well as associated pathway activation, was found to play the greatest role in the protective effects of menthol against inflammatory damage or association with protection against chronic inflammation.

CONCLUSION

This review mainly concludes the progress in menthol's anti-inflammatory activity. Further studies are needed to establish relationships between the mechanisms of action and to clarify the clinical relevance of any anti-inflammatory effects.

Subjective changes in nasal patency after chewing a menthol-containing gum in patients with olfactory loss

CONCLUSION

The subjective increase in nasal patency after oral menthol application depends on olfactory function. In patients with relatively low olfactory sensitivity, this effect is small or absent. It was hypothesized that this may also modulate the sensation of nasal blockage.

OBJECTIVE

Menthol stimulates the nasal trigeminal nerve, resulting in a subjectively increased nasal airflow and patency without objectively measurable changes. Patients suffering from olfactory impairment also express a reduced nasal trigeminal sensitivity. The aim of this investigation was to examine the effect of menthol on nasal patency ratings in a group of patients suffering from olfactory dysfunction.

METHODS

A group of 92 patients with olfactory impairment was included in this study. Olfactory function was assessed using the 'Sniffin' Sticks.' Patients were instructed to chew a menthol-containing gum for 30 s, after which they rated the change in nasal patency on a categorical scale.

RESULTS

Patients who rated the change in nasal patency as pronounced scored higher on the Sniffin' Sticks olfactory test compared to patients who experienced little or no change in nasal patency after chewing the menthol-containing gum. On average, similar changes could be observed for all etiologies of olfactory impairment included in this study.

The effects of menthol on reaction time and nasal sensation of airflow in subjects suffering from the common cold

The effects of sucking a lozenge containing 11 mg L-menthol on reaction time and nasal sensation were investigated in a double blind trial on 60 subjects suffering from the common cold. Reaction time was determined by measuring the response time to a stimulus presented on a microcomputer screen and nasal sensation was scored on a visual analogue scale. Menthol ingestion compared to placebo caused a significant increase in nasal sensation of airflow which persisted for up to 30 min. The simple and choice reaction times measured before ingestion of the lozenge were similar to those found in healthy uninfected subjects and there was no change in reaction time after ingestion of menthol.

Prevention of colonic spasm using L-menthol in colonoscopic examination

PURPOSE

The detailed efficacy of intraluminal L-menthol for preventing colonic spasm is not known. The aim of this study was to evaluate the effectiveness of L-menthol in preventing colonic spasm during colonoscopy.

METHODS

We analyzed 65 patients (mean age: 71.7 years; 49 men and 16 women) who were administered 0.8% L-menthol (MINCLEA, Nihon Seiyaku, Tokyo, Japan) intraluminally for severe colonic spasm during colonoscopic examination at Kyoto Prefectural University of Medicine between February 2012 and May 2013. The efficacy of L-menthol was defined as the absence of colonic spasm during a period of 30 s, and its effect was evaluated at 30 s, 1 min, and 5 min after administration. Additionally, various characteristics of these patients were analyzed. Twenty-seven patients with severe colonic spasm were administered intraluminal water and assessed as controls.

RESULTS

L-Menthol was effective in preventing colonic spasms in 60.0%, 70.8%, and 46.5% of patients at 30 s, 1 min, and 5 min, respectively. In contrast, water was effective in 22.2%, 29.6%, and 48.1% of patients at 30 s, 1 min, and 5 min, respectively. There was a significant difference about the efficacy at 30 s and 1 min between L-menthol and water (P = 0.0009, P = 0.0006).

CONCLUSIONS

L-Menthol (0.8%) was effective in preventing colonic spasm during colonoscopic examination.

Impact of elevated core temperature on cognition in hot environments within a military context

PURPOSE

Cognition can be impaired during exercise in the heat, potentially contributing to military casualties. To our knowledge, the independent role of elevated core temperature during exercise has not been determined. The aim of the current study was to evaluate effects of elevated core temperature on cognition during physically encumbering, heated exercise, and to determine whether the perceptual cooling effects of menthol preserves cognition.

METHODS

Eight participants complete three trials in randomised order: one normothermic (CON) and two with elevated (38.5°C) core temperature, induced by prior immersion in neutral versus hot water The CON trial and one hot trial (HOT) used a water mouth-rinse following each cognitive task of the trial, (HOT) while the other used a menthol mouth-rinse (MENT). Participants walked in humid heat (33°C, 75% relative humidity) in military clothing, completing a cognitive battery of reaction time, perceptual processing, working memory, executive function, cognitive flexibility, vigilance, and declarative memory.

RESULTS

No differences in cognitive performance were observed between any conditions. Near-infrared spectroscopy showed greater oxygenated haemoglobin tissue content in HOT and MENT compared to CON (ΔO₂Hb-deO₂Hb: 2.3 ± 4.5 µM, p < .024), and lower deoxygenated haemoglobin in MENT than in CON or HOT (p = .017), suggesting higher brain metabolism during the more stressful conditions.

CONCLUSION

Moderately elevated core (38.5°C) and skin temperature does not appear to impair cognitive performance during exercise despite mildly elevated cerebral metabolism. The effects of menthol remain undetermined due to the lack of heat-mediated cognitive impairment.