The Role of Menthol in Skin Penetration from Topical Formulations of Ibuprofen 5% in vivo

Peppermint and menthol: a review on their biochemistry, pharmacological activities, clinical applications, and safety considerations

In this manuscript, we conducted a comprehensive review of the diverse effects of peppermint on human health and explored the potential underlying mechanisms. Peppermint contains three main groups of phytochemical constituents, including essential oils (mainly menthol), flavonoids (such as hesperidin, eriodictyol, naringenin, quercetin, myricetin, and kaempferol), and nonflavonoid phenolcarboxylic acids. Peppermint exhibits antimicrobial, antioxidant, anti-inflammatory, immunomodulatory, anti-cancer, anti-aging, and analgesic properties and may be effective in treating various disorders, including gastrointestinal disorders (e.g., irritable bowel syndrome, dyspepsia, constipation, functional gastrointestinal disorders, nausea/vomiting, and gallbladder stones). In addition, peppermint has therapeutic benefits for psychological and cognitive health, dental health, urinary retention, skin and wound healing, as well as anti-depressant and anti-anxiety effects, and it may improve memory. However, peppermint has paradoxical effects on sleep quality and alertness, as it has been shown to improve sleep quality in patients with fatigue and anxiety, while also increasing alertness under conditions of monotonous work and relaxation. We also discuss its protective effects against toxic agents at recommended doses, as well as its safety and potential toxicity. Overall, this review provides the latest findings and insights into the properties and clinical effects of peppermint/menthol and highlights its potential as a natural therapeutic agent for various health conditions.

Optimization and Evaluation of the In Vitro Permeation Parameters of Topical Products with Non-Steroidal Anti-Inflammatory Drugs through Strat-M® Membrane

Pharmaceutical products containing non-steroidal anti-inflammatory drugs (NSAIDs) are among the most prescribed topical formulations used for analgesic and antirheumatic properties. These drugs must overcome the skin barrier to cause a therapeutic effect. Human skin has been widely used as a model to study in vitro drug diffusion and permeation, however, it suffers from many limitations. Therefore, to perform in vitro permeation test (IVPT), we used a Strat-M^® membrane with diffusion characteristics well-correlated to human skin. This study’s objective was to optimize the IVPT conditions using Plackett–Burman experimental design for bio-predictive evaluation of the in vitro permeation rates of five non-steroidal anti-inflammatory drugs (diclofenac, etofenamate, ibuprofen, ketoprofen, naproxen) across Strat-M^® membrane from commercial topical formulations. The Plackett–Burman factorial design was used to screen the effect of seven factors in eight runs with one additional center point. This tool allowed us to set the sensitive and discriminative IVPT final conditions that can appropriately characterize the NSAIDs formulations. The permeation rate of etofenamate (ETF) across the Strat-M^® membrane was 1.7–14.8 times faster than other NSAIDs from selected semisolids but 1.6 times slower than the ETF spray formulation.

Topical NSAIDs for acute local pain relief: in vitro characterization of drug delivery profiles into and through human skin

OBJECTIVE

The efficacy of topical nonsteroidal anti-inflammatory drugs (NSAIDs) relates not only to the individual NSAID used but also to differences in formulation design. The aim of this study was to investigate the fundamental differences in ibuprofen and diclofenac drug delivery vehicles, specifically gels and plasters, compared to a recently launched 200 mg ibuprofen medicated plaster and characterize the resulting dermatologic-pharmacokinetic profiles into and through ex vivo human skin layers.

METHODS

In vitro skin permeation testing over 24 h and sacrificial timepoint penetration experiments (at 1, 4, 8, 12, and 24 h) were conducted using an automated flow-through diffusion cell system. The amount of drug delivered to the epidermis, dermis, and receptor solution (representing deeper tissue) was determined by liquid chromatography-tandem mass spectrometry. Skin protein binding of ibuprofen and diclofenac was investigated by spiking skin homogenate with increasing concentrations of each drug and determining the fraction unbound.

RESULTS

Differences were observed in the amount of drug recovered at sacrificial timepoints and rate at which drug was delivered to the target site between plaster and gel formulations of ibuprofen and diclofenac and between plaster formulations of the same drug (ibuprofen). While the amount of drug quantified at sacrificial timepoints did not necessarily determine in vivo flux rates, differences in drug distribution within the skin layers indicated where drug reservoirs were formed.

CONCLUSIONS

These findings highlight the importance of intelligent formulation design in determining NSAID delivery through skin layers. Further work is required to quantify drug delivery into deeper tissues and the resultant local anti-inflammatory effects.

Formulation Development, Characterization, and Evaluation of a Novel Dexibuprofen-Capsaicin Skin Emulgel with Improved In Vivo Anti-inflammatory and Analgesic Effects

Transdermal application of analgesics allows efficient and painless delivery of medication with minimum side effect. This study was designed with the aim to formulate and characterize dexibuprofen-capsaicin emulgel for transdermal drug delivery with improved anti-inflammatory and analgesic effects. The emulgel was prepared and evaluated for physical examination, stability, spreadability, rheological behavior, viscosity, drug content determination, FTIR analysis, and ex vivo studies. Anti-inflammatory (carrageenan-induced paw edema) and analgesic (hot plate latency test) effects were determined in Sprague-Dawley rats. The dexibuprofen-capsaicin emulgel showed good physical appearance and stability having average pH 5.5 to 6.0, conductivity 73-76 s/m, spreadability (12-)17 g cm/s, drug content 102.84% ± 0.53 (for capsaicin) and 94.09% ± 0.41 (for dexibuprofen), and FTIR compatibility. It was noted that 86.956% ± 1.46 (with 100 mg menthol), 76.687% ± 1.21 (75 mg menthol), and 65.543% ± 1.71 (without menthol) of capsaicin were released. Similarly 81.342% ± 1.21 (with 100 mg menthol), 72.321% ± 1.31 (75 mg menthol), and 52.462% ± 1.23 (without menthol) of dexibuprofen were released. The cumulative amount of capsaicin permeated through rabbit skin was 9.83 ± 0.037 μg/cm² with 100 mg menthol (as permeation enhancer), 7.23 ± 0.037 μg/cm² with 75 mg menthol, and 2.23 ± 0.061 μg/cm² without menthol after 6.5 h. The permeation of dexibuprofen was 19.53 ± 0.054 μg/cm², 13.87 ± 0.032 μg/cm², and 3.83 ± 0.074 μg/cm². Carrageenan-induced paw edema of rat was effectively inhibited by the optimized emulgel. Similarly it was observed that DCE5 shows higher analgesic activity compared with marketed diclofenac sodium emulgel (Dicloran®). The conclusion of this research study evidently indicated a promising synergistic potential of dexibuprofen-capsaicin emulgel as an alternative to the conventional topical dosage form.

Transdermal Administration of Ibuprofen-Loaded Gel: Preparation, Pharmacokinetic Profile, and Tissue Distribution

The purpose of this study was to compare the pharmacokinetics and tissue distribution of ibuprofen (IBU) gel in female rats after transdermal administration through the skin of the abdomen and back. IBU was used as the model drug to prepare carbomer gel. After the abdominal and back administration, the concentration of IBU in rat plasma was detected by high-performance liquid chromatography (HPLC). Besides, the contents of IBU in the uterus, heart, liver, spleen, lung, and kidney were detected, respectively, to clarify the distribution characteristics in vivo. Through abdominal route, the AUC0- ∞ (area under the concentration-time curve from time zero to infinity) of uterus was 424.75 μg/g h, which is 3.60 times higher than that of plasma, and was significantly higher than that of other tissues (P < 0.0001). Tmax (peak time) of uterus and plasma was 4 h and 2 h, respectively. Upon transdermal application of IBU to the back, the AUC0-∞ of uterus was 75.47 μg/g h, which is 12.63 times lower than that of plasma, while Tmax of uterus and plasma was not lower than 20 h. These results indicated that IBU entered the blood circulation through abdominal administration in a small amount and mainly of the drug entered the uterus, while IBU entered the blood circulation and redistributed to tissues after absorption through the dorsal skin slowly. IBU could effectively reach the uterus and have a certain targeting through abdominal administration, which provides a prospect for clinical transdermal administration in the treatment of dysmenorrhea.

Menthol-modified casein nanoparticles loading 10-hydroxycamptothecin for glioma targeting therapy

Chemotherapy outcomes for the treatment of glioma remains unsatisfactory due to the inefficient drug transport across the blood-brain barrier (BBB) and insufficient drug accumulation in the tumor region. Although many approaches, including various nanosystems, have been developed to promote the distribution of chemotherapeutics in the brain tumor, the delivery efficiency and the possible damage to the normal brain function still greatly restrict the clinical application of the nanocarriers. Therefore, it is urgent and necessary to discover more safe and effective BBB penetration and glioma-targeting strategies. In the present study, menthol, one of the strongest BBB penetration enhancers screened from traditional Chinese medicine, was conjugated to casein, a natural food protein with brain targeting capability. Then the conjugate self-assembled into the nanoparticles to load anti-cancer drugs. The nanoparticles were characterized to have appropriate size, spheroid shape and high loading drug capacity. Tumor spheroid penetration experiments demonstrated that penetration ability of menthol-modified casein nanoparticles (M-CA-NP) into the tumor were much deeper than that of unmodified nanoparticles. In vivo imaging further verified that M-CA-NPs exhibited higher brain tumor distribution than unmodified nanoparticles. The median survival time of glioma-bearing mice treated with HCPT-M-CA-NPs was significantly prolonged than those treated with free HCPT or HCPT-CA-NPs. HE staining of the organs indicated the safety of the nanoparticles. Therefore, the study combined the advantages of traditional Chinese medicine strategy with modern delivery technology for brain targeting, and provide a safe and effective approach for glioma therapy.

Biochemical Responses of Wheat Seedlings on the Introduction of Selected Chiral Ionic Liquids to the Soils

In this study, new chiral ionic liquids (CILs) were obtained from the natural-origin material (1 R,2 S,5 R)-(-)-menthol. The physicochemical characteristics of the studied imidazolium salts were investigated. The obtained 3-ethyl-1-[(1 R,2 S,5 R)-(-)-menthoxy-methyl]imidazolium salts are nonvolatile, nonflammable, and stable in air, in contact with water, and in commonly used organic solvents. The influences of the obtained chiral salts on physiological and biochemical parameters were determined for wheat ( Triticum aestivum L.) seedlings. Both salts led to changes in plant metabolism, which resulted in decreased assimilation pigments, decreased fresh weight, and increased dry weight and proline in wheat seedlings. Moreover, the growth of the above-ground parts and roots was inhibited. Additionally, there was a drop in the potential and germination capacity of wheat seeds after using the highest concentrations of the ionic liquids. The salts caused oxidative stress in wheat seedlings, which was demonstrated by increased malondialdehyde content. In response, the plants engaged their defensive system against free oxygen radicals, which resulted in increased catalase and peroxidase activity and decreased H₂O₂ levels in the plants. There were no changes in the activity of superoxide dismutase. All of the changes observed in the levels of determined biomarkers of oxidative stress in the plants were linearly correlated with the increase in the concentrations of the chiral ionic liquids in the soil. The salt with hexafluorphosphate anion exhibited slightly higher toxicity toward wheat seedlings than the other salt. The CILs led to premature aging of plants, which was demonstrated by the increase in peroxidase activity and a decrease of chlorophyll in the seedlings. The experiment also showed good correlation between the increase in peroxidase activity and the decrease in chlorophyll level, which proves that the decrease in chlorophyll content resulted from not only the increase in CILs concentration in the soil but also the increased POD activity, which leads to the damage of chlorophyll particles.

Development, Characterization and Transdermal Delivery of Dapsone and an Antibiotic Entrapped in Ethanolic Liposomal Gel for the Treatment of Lapromatous Leprosy

Background and Objective:

Applying Ethosomal Gels (EGs) in transdermal drug delivery systems has evoked considerable interest because of their good water-solubility and biocompatibility. The aim of present study was to prepare and characterize ethosomes of antileprotic drug Dapsone (DAP) together with an antibiotic Cloxacillin Sodium (CLXS) which may deliver these drugs to targeted site more efficiently than marketed gel preparation of DAP and also overcome the problems related with oral administration of CLXS.

Methodology:

Ethosomes were prepared by cold method then characterized for particle size, Entrapment Efficiency (EE), zeta potential and permeation studies. Vesicular size was determined by Scanning Electron Microscopy (SEM) and found to be varied from 127±9.01 to 215±7.23 nm depending on the concentrations of soya lecithin and ethanol.

Results:

The average percent drug entrapment efficiency of formulations ranged between 52.31% to 73.51% and 49.07% to 71.91% for DAP and CLXS respectively. The high ethanol concentration in ethosomes has shifted the vesicular charge from positive to negative. It was observed that F1 and F2 formulations were having zeta potential of -25.08±1.03 mV and -50.11±1.97 mV respectively and do not aggregate rapidly. The drug release of ethosomes ranged from 84.68% to 96.58% and 64.89% to 84.21% for DAP and CLXS respectively. Ethosomal gel was prepared with optimized ethosome and studied for its release and physicochemical characteristics.

Conclusion:

Finally, G5 demonstrated better (p < 0.05) antileprotic effect to improve effectiveness, stability and to reduce side effects and toxicity associated with the chosen drugs in order to treat Leprosy.

Influence of paeoniflorin and menthol on puerarin transport across MDCK and MDCK-MDR1 cells as blood–brain barrier in vitro model

Objective

Our objective of this research was (1) to investigate the transport characteristics of puerarin through MDCK-MDR1 and MDCK cells and (2) to evaluate the effects of paeoniflorin and menthol on puerarin transport so as to (3) explore the enhancement mechanism.

Methods

The cytotoxicity of drugs on MDCK and MDCK-MDR1 was evaluated by the MTT assay, and the transport studies were performed in both directions. The membrane fluidity was evaluated by fluorescence recovery after photobleaching, and the membrane potential was estimated by the accumulation of DiBAC4(3) in the cells.

Key findings

Puerarin showed relatively poor absorption and purely passive diffusion. However, the efflux ratio of puerarin was &lt;2 in MDCK-MDR1 models, which suggested puerarin was not P-gp substrates so as to the P-glycoprotein activity determination of puerarin. With the existence of menthol, the transcellular transport of puerarin increased and puerarin transport significantly increased when co-administrated with paeoniflorin and menthol.

Conclusions

The enhancing effect of paeoniflorin and menthol may be attributed to the significant enhancement on cell membrane fluidity, the decrease in membrane potential. Immunostaining results indicated that menthol behaved as transport enhancer by disassembly effect on tight junction integrity.

Exploring the conformational landscape of menthol, menthone, and isomenthone: a microwave study

The rotational spectra of the monoterpenoids menthol, menthone, and isomenthone are reported in the frequency range of 2–8.5 GHz, obtained with broadband Fourier-transform microwave spectroscopy. For menthol only one conformation was identified under the cold conditions of the molecular jet, whereas three conformations were observed for menthone and one for isomenthone. The conformational space of the different molecules was extensively studied using quantum chemical calculations, and the results were compared with molecular parameters obtained by the measurements. Finally, a computer program is presented, which automatically identifies different species in a dense broadband microwave spectrum using calculated ab initio rotational constants as initial input parameters.

Menthol relaxes rat aortae, mesenteric and coronary arteries by inhibiting calcium influx

Menthol, a naturally occurring compound in mint, is known to give cold sensation. However, previous findings about its pharmacological activity in blood vessels are full of paradox. The present study investigated the action of menthol on vascular reactivity in different arteries isolated from male Sprague-Dawley rats, e.g. aortae, main mesenteric arteries and coronary arteries. The arterial segments were suspended in organ bath or in wire myograph for measurement of isometric force. Menthol concentration-dependently relaxed all three arteries with similar relaxing sensitivity in arteries contracted by different contractors, KCl, U46619 (9,11-dideoxy-9α,11α-methanoepoxy Prostaglandin F2α) and phenylephrine. Menthol-induced relaxations were unaffected by nitric oxide synthase inhibitor L-NAME, soluble guanylyl cyclase inhibitor ODQ, or mechanical removal of endothelium. Menthol also concentration-dependently suppressed 60mM KCl-induced constriction and CaCl2-induced contraction in Ca(2+)-free K(+)-containing solution. Calcium fluorescent imaging using fluo-4 showed that 10 min-incubation with 1mM menthol inhibited 60mM KCl-induced Ca(2+) influx in rat aortic smooth muscle cell line A7r5 and vascular smooth muscle of coronary arteries. To conclude, menthol induces relaxation and inhibits contraction in rat aortae, mesenteric and coronary arteries primarily through inhibiting Ca(2+) influx via nifedipine-sensitive Ca(2+) channels in vascular smooth muscle.

Finite and infinite dosing: difficulties in measurements, evaluations and predictions

Due to the increased demand for reliable data regarding penetration into and permeation across human skin, assessment of the absorption of xenobiotics has been gaining in importance steadily. In vitro experiments allow for determining these data faster and more easily than in vivo experiments. However, the experiments described in literature and the subsequent evaluation procedures differ considerably. Here we will give an overview on typical finite and infinite dose experiments performed in fundamental research and on the evaluation of the data. We will point out possible difficulties that may arise and give a short overview on attempts at predicting skin absorption in vitro and in vivo.

Menthol toxicity: an unusual cause of coma

The US Food and Drug Administration (FDA) consider menthol an effective substance, which help in common cold symptoms and labeled to have low toxicity profile. Direct exposure to high menthol amount has been reported in animal; but no studies have been done to show the effect of menthol on long-term use in humans. Up to our knowledge we are reporting a rare case of chronic exposure to significant amount of menthol associated with cutaneous, gastrointestinal and neurological manifestations.

Enhancement of gene transfer efficiency in the Bcap-37 cell line by dimethyl sulphoxide and menthol

Simple and efficient gene transfer into the nucleus would facilitate non-viral gene delivery. One promising method of non-viral gene delivery is to apply penetration enhancers. Chemicals, such as dimethyl sulfoxide (DMSO) and menthol, may have promise as non-toxic vehicles in improving gene transfer efficiency. In this study, the cytotoxic effects of DMSO and menthol were evaluated using MTT assays. Gene delivery efficiency in a human breast cancer cell line (Bcap-37) was investigated by quantitative PCR, fluorescence microscopy and flow cytometry. Non-toxic concentrations of DMSO (2%) and menthol (12.5 µM) enhanced the efficiency of liposome-mediated gene delivery in Bcap-37 cells. Quantitative PCR results showed that growth hormone (GH) mRNA expression in the post-menthol and pre-DMSO treatment groups was 10-fold higher compared to that in the liposome group, while in the pre-menthol and post-DMSO treatment groups, a 30-fold increase in GH mRNA expression was observed. Both DMSO and menthol treatments increased green fluorescent protein (GFP) expression efficiency as shown by fluorescence microscopy experiments. Compared to the liposome group, the number of positive cells in the pre-menthol and post-DMSO treatment groups was significantly increased by 15%. Furthermore, cell cycle analysis demonstrated that there were significant differences among the DMSO-treated group, the menthol-treated group and the normal group, which implied different effects of DMSO and menthol treatments. In conclusion, both non-toxic and harmless DMSO (2%) and menthol (12.5 µM) treatments improve gene transfer efficiency, while post-DMSO treatment may be the most effective protocol in increasing transgene expression efficiency.

The CAM-LDPI method: a novel platform for the assessment of drug absorption

OBJECTIVES

This study aimed to explore the use of the chicken chorioallantoic membrane (CAM) with laser doppler perfusion imaging (LDPI) as a platform to assess absorption of vasoactive drugs.

METHODS

The optimal age of the CAM to be employed in the test and the indicator of vasoactivity were first established. Test substances that included common solvents and vasoactive drugs were tested on the CAM surface to determine their irritancy and blood perfusion effects.

KEY FINDINGS

Insignificant changes in blood perfusion were observed with deionized water, 0.9% w/v soldium chloride and 5% w/v glucose monohydrate, as well as theophylline and glucagon. Complex changes in blood perfusion were detected with ethanol, N-methyl-2-pyrrolidone, glycerin and propranolol. Both caffeine and glyceryl trinitrate resulted in a drop in blood perfusion.

CONCLUSIONS

It was concluded that the LDPI offers a rapid and non-invasive method to measure blood perfusion in the CAM. The latter provides a potentially useful platform in formulation studies to evaluate the effects of additives on drug absorption using caffeine or glyceryl trinitrate as model drugs.

Effect of menthol on ocular drug delivery

BACKGROUND

To assess how safe and effective it is to use menthol as a permeability enhancer in ophthalmic drug delivery systems.

METHODS

In this study, the effect of menthol on permeability of dexamethasone disodium phosphate in the cornea and sclera was investigated in vitro. Application of topical drops and subconjunctival injection of dexamethasone disodium phosphate with or without 0.1% menthol was administered to rabbit eyes, and the drug concentration was detected in aqueous humor, cornea, vitreous, and retinochoroidal tissues. The safety of menthol was assessed on the basis of corneal hydration level, Draize test, electroretinography (ERG), and histological examination.

RESULTS

0.05% and 0.1% menthol significantly enhanced the penetration of dexamethasone in the cornea, but did not change the dexamethasone penetration in sclera in vitro. When topical drops of dexamethasone containing 0.1% menthol were administered, a significantly increased concentration of dexamethasone in the cornea and aqueous humor tissues was reported, but dexamethasone concentrations remained unaffected in the retina-choroid tissues. On the other hand, increased drug concentration in aqueous humor, cornea, vitreous and retinochoroidal tissues was achieved through subconjunctival injection. No signs of irritation were observed when menthol was administered at concentrations ranging from 0.025%-0.1%; moreover, no substantial toxic reactions were observed in corneal hydration level, electrophysiological, or histological examinations after the addition of 0.1% menthol.

CONCLUSIONS

Menthol may improve the ocular penetration of a drug in a transcorneal and transscleral drug delivery system without causing toxic reactions.

In vitro permeation and in vivo anti-inflammatory and analgesic properties of nanoscaled emulsions containing ibuprofen for topical delivery

INTRODUCTION

As a topical delivery system, a nanoscaled emulsion is considered a good carrier of several active ingredients that convey several side effects upon oral administration, such as nonsteroidal anti-inflammatory drugs (NSAIDs).

OBJECTIVE

We investigated the in vitro permeation properties and the in vivo pharmacodynamic activities of different nanoscaled emulsions containing ibuprofen, an NSAID, as an active ingredient and newly synthesized palm olein esters (POEs) as the oil phase.

METHODOLOGY

A ratio of 25:37:38 of oil phase:aqueous phase:surfactant was used, and different additives were used for the production of a range of nanoscaled emulsions. Carbopol® 940 dispersion neutralized by triethanolamine was employed as a rheology modifier. In some circumstances, menthol and limonene were employed at different concentrations as permeation promoters. All formulae were assessed in vitro using Franz diffusion cell fitted with full-thickness rat skin. This was followed by in vivo evaluation of the anti-inflammatory and analgesic activities of the promising formulae and comparison of the effects with that of the commercially available gel.

RESULTS AND DISCUSSION

Among all other formulae, formula G40 (Carbopol® 940-free formula) had a superior ability in transferring ibuprofen topically compared with the reference. Carbopol® 940 significantly decreased the amount of drug transferred from formula G41 through the skin as a result of swelling, gel formation, and reduction in drug thermodynamic activity. Nonetheless, the addition of 10% w/w of menthol and limonene successfully overcame this drawback since, relative to the reference, higher amount of ibuprofen was transferred through the skin. By contrast, these results were relatively comparable to that of formula G40. Pharmacodynamically, the G40, G45, and G47 formulae exhibited the highest anti-inflammatory and analgesic effects compared with other formulae.

CONCLUSION

The ingredients and the physical properties of the nanoscaled emulsions produced by using the newly synthesized POEs succeeded to deliver ibuprofen competently.

Niaouli oils from different sources: analysis and influence on cutaneous permeation of estradiol in vitro

Previous studies in vitro had identified niaouli essential oil (NEO) as a valuable transdermal permeation promoter for estradiol (ES). Subsequent considerations on the complex issue of NEO provenance and composition stimulated the present investigation, which was aimed at defining the composition of NEOs obtained from four different sources, at evaluating their influence on transdermal permeation of ES through hairless mouse skin, and at formulating and evaluating simpler terpene mixtures mimicking the NEOs' composition. While all oils contained 1,8-cineol (eucalyptol) as the main component, appreciable variations in composition could be evidenced, originating differences on the ES cutaneous permeation. Two artificial mixtures containing the same proportions of the main terpenes present in each oil (except the commercially unavailable gamma-terpineol) proved equal or significantly superior in activity when compared with the original oils. It is felt that this study might contribute to the formulation of terpene mixtures acting more efficiently and reproducibly with respect to natural NEOs, whose complex and variable composition, depending on growing place, season, and extraction process, is well documented in the relevant literature.