Scientific Name(s): Leptospermum scoparium J.R. Forst. et G. Forst.
Common Name(s): Manuka oil, Red manuka, Tea tree, Teatree
L. scoparium is the only Leptospermum species native to New Zealand. Its size ranges from a creeping plant to a small tree (of 8 m in height) and it is widely distributed in various climatic and altitudinal zones in New Zealand. The physical characteristics, such as flower and leaf color, leaf size and shape, branching habit, and foliage density vary considerably among populations. Manuka oil should not be confused with Melaleuca alternifolia (see Tea Tree Oil monograph). (USDA)1, 2, 3, 4
Early New Zealand records indicate that the plant's bark, leaves, sap, and seed capsules were used in beverages and medicinal preparations.4 The plant was valued for its medicinal properties and wood by the indigenous Maori people; the wood was utilized for gardening tools, fishing, housing structures, and weapons.2, 5
Captain James Cook used the leaves of the plant as a tea to combat scurvy during long explorations of the southern hemisphere; early European settlers of New Zealand adopted Captain Cook's use of the plant as a tea.2
Commercial development of the essential oils has led to a range of OTC products marketed in New Zealand and exported to European and Asian markets. These products are used for topical treatment of various conditions including the following: Fungal and bacterial skin infections; inflammation from sunburn, insect bites, or joint pain; eczema or psoriasis. The oils also are used in perfumes and soaps.2
The L. scoparium populations of New Zealand are highly variable in oil chemical composition and activity.6, 7 Standardized steam distillation and gas chromatography-mass spectrometry of the essential oils of 15 New Zealand L. scoparium populations identified the following in various quantities per species: alpha-pinene, beta-pinene, myrcene, rho-cymene, 1,8-cineole, linalol, methylcinnamate, alpha-farnesine, isoleptospermone, leptospermone, sesquiterpenes such as cadina-3,5-diene and delta-amorphene, and triketones.3, 4, 6
Triterpenoids and flavonoids (including methylated and methoxylated flavonoids such as 5,7-dimethoxyflavone, 5-hydroxy-7-methoxy-6-methylflavone, and 5-hydroxy-7-methoxy-6,8-dimethylflavan-3-one) have been identified in a dichloromethane extract of L. scoparium.8, 9 Oligosaccharide components include maltose (the major component), isomaltose (or maltulose), kojibiose, turanose (or gentiobiose), and nigerose.10
The average content of total flavonoids in New Zealand manuka (L. scoparium) honey was 3.06 mg per 100 g honey; the main flavonoids consisted of quercetin, isorhamnetin, chrysin, and luteolin.11 The potentially active methylglyoxal, derived from the precursor dihydroxyacetone, has been identified in the flowers of certain species of Leptospermum native to New Zealand and Australia, and is found in Manuka honey.12, 13
Uses and Pharmacology
Manuka oil has selective antibacterial activity against gram positive organisms14 such as Staphylococcus aureus and Micrococcus luteus.15 Manuka oil has little to no activity against gram-negative organisms such as Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Proteus vulgaris.14, 15, 16
Some studies document the activity of L. scoparium against fungi and yeast;14, 16 however, there are limited data to support these claims for L. scoparium as compared with other species of Myrtaceae (eg, kanuka or Kunzea ericoides ).17
Studies have been conducted on wound healing in animals, especially in horses.12
Studies have evaluated the efficacy of Manuka honey in healing infected wounds. In neuropathic diabetic foot ulcers, Manuka honey-impregnated dressings increased healing rates and reduced the need for antibiotics in a clinical study of 63 patients versus saline dressings. However, the percentage of healed ulcers was not affected.18 While the role of honey as an anti-infective agent has been described, the additive efficacy of Manuka in the honey has not been established in robust clinical trials.12, 13
Anti-inflammatory and immunomodulatory effects have been described in published reviews.13
A small clinical trial (n=19) evaluated Manuka with Kanuka essential oils as a gargle for benefit on radiotherapy-induced mucositis and symptoms. Mucositis reportedly developed significantly later in patients with the active gargle. The small sample size of most variables prevented further statistical comparisons. Mean pain scores gradually increased over treatment time with fewer patients in the active gargle group experiencing scores of 3 or higher and going the longest until that level of pain was reached; this was also reflected in the use of daily analgesics. Interestingly, patients with more family members present during treatment tended to report more frequent and more severe pain than those without family members present.19
Manuka, as the honey, has been studied in radiotherapy-induced mucositis in limited clinical trials finding no improvement on mucositis, and some effect on bacterial infection.20, 21( Bardy, Hawley) A study conducted in patients with rhinosinusitis, using mankua honey nasal spray, found no endoscopically validated improvement in symptoms.22
The pharmacological action of manuka oil for treating diarrhea, colds, and inflammation was studied on a field-stimulated guinea pig ileum. Manuka oil induced a spasmolytic effect17, 23; the mechanism of action is likely to be the result of a postsynaptic mechanism and associated with cAMP.23
L. scoparium contains a lipophilic flavonoid that specifically interacts with benzodiazepine receptors in the GABA-A receptor-chloride channel complex. A sedating and potentially anxiolytic effect was recorded in a locomotion study with rats.24, 25
There are no reported clinical studies of manuka oil on which dosage recommendations can be based.
Manuka honey has been used anecdotally as a prebiotic. A study evaluated the safety of consuming 20 g of honey daily for 4 weeks found no adverse effects on GI flora.26 20 mL of the honey taken 4 times daily for 6 weeks was evaluated in oral mucositis.20
Pregnancy / Lactation
None well documented.
Clinical studies of Manuka honey in mucositis found tolerability of dosage regimens to be poor. (Bardy, Hawley)
There are limited clinical toxicological data on manuka oil in the scientific literature. Anecdotal information from OTC use of topical manuka oil products suggests good potential for its future use as an antimicrobial agent.2 Avoid use during pregnancy because of reported spasmolytic activity.17, 23
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