Monograph: |
Mentha oil
The volatile oil obtained by distillation from the fresh over-
ground pans of Mentha x piperita (Labialae) and rectified if
necessary.
It is a colourless, pale yellow, or greenish-yellow oil with the
characteristic odour of mentha and a pungent aromatic
cooling taste. It contains menthol, menthone. and menthyl ac-
etate. The Ph. Eur. specifies 2.8 to 10% menthyl acetate, 30 to
50% menthol, and 14 to 32% menthone. The USNF specifies
not less than 57i- of esters calculated as menthyl acetate and
not less than 50% of total menthol, free and as esters.
Miscible with alcohol: soluble I in 3 of alcohol (70%) with
slight opalescence: miscible with ether and with dichio-
romethane. Store at a temperature not exceeding 40Β° in air-
tight containers. Protect from light.
The Pharmaceutical Society's Department of Pharmaceutical
Sciences found that PVC bottles softened and distorted fairly
rapidly in the presence of mentha oil, which should not be
stored or dispensed in such bottles.
Adverse Effects and Precautions
Mentha oil can be irritant and may rarely cause hypersen-
sitivity reactions. Reported reactions include erythematous
skin rash. headache, bradycardia, muscle tremor, and ataxia.
Heanbum has also been reported.
Eftects on the cardiovascular system. Idiopathic atrial
fibrillation in 2 patients addicted to 'menthas'. Normal
rhythm was restored when mentha-sucking ceased.'
Hypersensitivity. Exacerbation of asthma, with wheezing
and dyspnoea, associated with the use of paste-based tooth-
pastes containing mentha or wintergreen as a flavouring.'
Interactions
Reactions may be more likely if mentha oil is taken in
conjunction with alcohol. Enteric-coated capsules containing
mentha oil should not be taken immediately after food or
with antacids.
Uses and Administration
Mentha oil is an aromatic carminative which relaxes gas-
tro-intestinal smooth muscle and relieves flatulence and colic.
Enteric-coated capsules containing mentha oil are used
for the relief of symptoms of the irritable bowel syndrome or
gastro-intestinal spasm secondary to other disorders. Usual
doses are 0.2 mL three times daily by mouth, half to one hour
before food. increased to 0.4 mL three times daily if neces-
sary.
Mentha oil is also used as a flavour and with other volatile
agents in preparations for respiratory-tract disorders.
Mentha leaf, the source of the oil, has also been used for
its carminative and flavouring properties.
Gastro-intestinal disorders. Any effect of mentha oil
on the irritable bowel syndrome may be through a local action
on the gastro-intestinal tract. Pharmacological studies
have shown that menthol, the major constituent of mentha
oil, has properties similar to those of calcium-channel antag-
onists and inhibits influx of calcium ions through smooth
muscle including that in the human gut.
The relaxant effect of mentha oil on the gastro-intestinal
tract has been used to reduce colonic spasm during endoscopy
by injecting the oil or a diluted suspension of the oil along the
biopsy channel of the colonoscope. Addition of mentha
oil to barium enema has also been tried and appears to reduce
spasm and reduce the need for intravenous antispasmodics.
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