Menthol

Synonyms: Hexahydrothymol; 2-isopropyl-5-methylcyclohexanol; 4-isopropyl-1-methylcyclohexan-3-ol; 3-p-menthanol; p-menthan-3-ol; dlmenthol; mentholum racemicum; menthomenthol; mentoli; mentolis; peppermint camphor; racemic menthol.

Description: Racemic menthol is a mixture of equal parts of the (1R,2S,5R)- and (1S,2R,5S)-isomers of menthol. It is a free-flowing or agglomerated crystalline powder, or colorless, prismatic, or acicular shiny crystals, or hexagonal or fused masses with a strong characteristic odor and taste. The crystalline form may change with time owing to sublimation within a closed vessel. The USP 32 specifies that menthol may be either naturally occurring l-menthol or synthetically prepared racemic or dl-menthol. However, the JP XV and PhEur 6.0, along with other pharmacopeias, include two separate monographs for racemic and l-menthol

Chemical Name: (1RS,2RS,5RS)-()-5-Methyl-2-(1-methylethyl)cyclohexanol

Flavoring agent; therapeutic agent.

• Menthol is widely used in pharmaceuticals, confectionery, and toiletry products as a flavoring agent or odor enhancer.

• In addition to its characteristic peppermint flavor, l-menthol, which occurs naturally, also exerts a cooling or refreshing sensation that is exploited in many topical preparations.

• Unlike mannitol, which exerts a similar effect due to a negative heat of solution, l-menthol interacts directly with the body’s coldness receptors. d-Menthol has no cooling effect, while racemic menthol exerts an effect approximately half that of l-menthol.

• When used to flavor tablets, menthol is generally dissolved in ethanol (95%) and sprayed onto tablet granules and not used as a solid excipient.

• Menthol has been investigated as a skin-penetration enhancer and is also used in perfumery, tobacco products, chewing gum and as a therapeutic agent.

• When applied to the skin, menthol dilates the blood vessels, causing a sensation of coldness followed by an analgesic effect.

• It relieves itching and is used in creams, lotions, and ointments.

• When administered orally in small doses menthol has a carminative action.

Incompatible with: butylchloral hydrate; camphor; chloral hydrate; chromium trioxide; b-naphthol; phenol; potassium permanganate; pyrogallol; resorcinol; and thymol.

Almost all toxicological data for menthol relate to its use as a therapeutic agent rather than as an excipient. Inhalation or ingestion of large quantities can result in serious adverse reactions such as ataxia and CNS depression, hypersensitivity reactions, severe abdominal pain, nausea, vomiting, vertigo, drowsiness, and coma. Although menthol is essentially nonirritant there have been some reports of hypersensitivity following topical application. In a Polish study approximately 1% of individuals were determined as being sensitive to menthol. There have been reports of apnea and instant collapse in infants after the local application of menthol to their nostrils.

May be harmful by inhalation or ingestion in large quantities; may be irritant to the skin, eyes, and mucous membranes. Observe normal precautions appropriate to the circumstances and quantity of material handled. Eye protection, chemical resistant gloves, and respirators are recommended. Avoid prolonged or repeated exposure.

d-Menthol; l-menthol; thymol.