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Constituents and Pharmacology
Various animal and human testing over the last 100 years or so has produced variable results. Some identified constituents showed stimulating activity, some sedative activity, and some no activity. In early testing, the original material used in the tests was not often identified precisely as to variety or even species, and where commercial herb samples were used, adulteration may have been a possibility.
Using modern analytical methods such as HPLC, it has become clear that there may be at least two major active fractions.
1. Lipid-soluble compounds:
A group of alpha-pyrones (6 major ones) with the 4-methoxy-2-pyrone ring system. The major compounds are kawain (34.5%), methysticin (20.8%), dihydrokawain (17.1%), dihydromethysticin (5.3%), and yangonin (0.8%). The percentages are based on the ethyl acetate extract (Smith, et al.). The total pyrone content of the rhizome is usually about 3-4% (Lewis & Lewis).
2. Water-soluble compounds:
A polar molecule of molecular weight 1000-10,000, showing a sedative effect in animal tests, has not yet been characterized.
Pharmacological effects such as cerebral depression, a heartbeat-steadying effect (Lewis & Lewis), and an anxiolytic (Singh, 1981) effect have been noted, and a number of animal tests have been performed--for a review .
Kava has been extensively studied as a treatment for anxiety.6 The amount often used in clinical trials is 100 mg of an extract (standardized to 70% kava-lactones) three times per day. Double-blind trials, including one that lasted six months, have shown that kava effectively reduces symptoms of anxiety in people with mild to moderate anxiety.7 8 One trial found that kava also reduced symptoms of anxiety in menopausal women.9 One trial found kava to be just as effective as benzodiazepines (a common class of drugs prescribed for anxiety) in treating mild anxiety over the course of six weeks.10
Kava has been extensively studied as a treatment for anxiety. The amount often used in clinical trials is 100 mg of an extract (standardized to 70% kava-lactones) three times per day. Double-blind trials, including one that lasted six months, have shown that kava effectively reduces symptoms of anxiety in people with mild to moderate anxiety. One trial found that kava also reduced symptoms of anxiety in menopausal women. One trial found kava to be just as effective as benzodiazepines (a common class of drugs prescribed for anxiety) in treating mild anxiety over the course of six weeks.
The chief constituent of kava-kava root, amounting to 49 per cent, is starch (Gobley, 1860). It also contains about 1 per cent of a neutral, tasteless, crystallizable principle called kavahin or methysticin (Morson, 1844; Cuzent, 1860). It is hardly soluble in cold water, easily soluble in alcohol and ether. C. Pomeranz (Chem. Centralbl., 1890, p. 124) found methysticin (C15H14O5) to be the methyl ester of methysticic acid (C14H12O5) which stands in close relationship to piperic acid of Fittig and Mielck (see Piperinum). Dragendorff (Heilpflanzen, 1899) differentiates methysticin from kavahin, stating the latter to be methylene protocatechuic aldehyde (which is the chemical name for heliotropin or piperonal). An alkaloid, kavaine, was isolated in 1889 by Lavialle (Amer. Jour. Pharm., 1889, p. 136). The active principle of kava-kava consists, however, in an acrid resin (2 per cent, Gobley, 1857) which was differentiated by Lewin (Pharm. Centralhalle, 1886, p. 72) into alpha-resin, which is a strong local anaesthetic, and the less active beta-resin.
Action, Medical Uses, and Dosage.-The root of Piper methysticum has a pleasant, somewhat lilac odor, and a slightly pungent, bitter and astringent taste, which augments the salivary discharge. It has marked general and local anaesthetic properties. It has been employed as a pleasant remedy in bronchitis, rheumatism, gout, gonorrhoea, and gleet, and has also been recommended as a powerful sudorific. It appears to exert its influence more especially upon diseased mucous membranes, and may be found useful in chronic catarrhal affections of various organs, and in chronic inflammation of the neck of the bladder. The action of the root varies, according to the amount taken; in small doses, it is tonic and stimulant; while in large doses it produces an intoxication, which, unlike that from alcohol, is of a reserved, drowsy character, and attended with confused dreams. The natives who use its infusion as an intoxicating beverage for a considerable length of time, are said to become affected with a dry, scaly, cracked, and ulcerated skin, and vision becomes more or less obscured. According to Kesteven, leprous ulcerations may be produced by its habitual use. M. Dupouy, who has given considerable attention to the therapeutical virtues of this drug, arrives at the following conclusions: Given in drink, kava is a sialagogue, but is not sudorific. In medicinal doses, it acts upon the stomach, similar to the bitter stimulants, increasing the appetite, without occasioning diarrhoea or constipation, and may prevent catarrhal affections of this portion of the digestive tube. It exerts a special stimulation upon the central nervous system, differing essentially from ethylic intoxication; and, as its taste is agreeable, one soon becomes a proselyte to it. It has a very powerful action upon aqueous diuresis, and may be classed among the most efficient diuretics. It does not occasion priapism, but, on the contrary, antagonizes it. It is endowed with remarkable and prompt blennostatic properties, augmenting the discharge previous to effecting its cure. It is of undoubted efficiency in acute vaginitis or urethritis, allaying the inflammation, causing the pain during micturition to disappear, when dysuria is present, and suppressing the mucopurulent catarrh from the vesico-urethral mucous membrane. It has, over other blennostatic agents, the marked advantages of being pleasant to take, of augmenting the appetite, of occasioning neither diarrhoea nor constipation, of alleviating or entirely subduing pain during urination, of completely changing the character of the discharge, and of effecting the cure in a very short time-10 or 12 days. He can not too highly recommend its employment, especially in the treatment of gonorrhoea. Ellingwood (Mat. Med., 1898) declares it of great value in subacute and slow forms of gonorrhoea, and especially in gleet. It is a remedy for nocturnal incontinence of urine in the young and old, when due most largely to muscular weakness.
The anticatarrhal action is probably due to the resin present, and the diuretic effects to the neutral crystallizable principle, methysticin or kavain. There may likewise be present some other active principle, not yet detected, to account for certain other influences following its employment. Piper methysticum has been successfully employed in atonic dyspepsia and in neuralgic or spasmodic dysmenorrhoea. Prof. Webster (Dynam. Therap.) regards it as our most reliable remedy for neuralgia, particularly of the parts supplied by the fifth cranial nerve, as in dental neuralgia (when not due to exposure of the dental pulp), neuralgic affections of the eyes, ears, etc., and in reflex neuralgias in other parts of the body, as gastric and intestinal neuralgia, abdominal neuroses, from prostatic, urethral, or testicular disorders, and pectoral pain due reflexly to nervous dyspepsia. He also suggests its employment in renal colic. Piper methysticum has proved useful in dropsy, intestinal catarrh, and in hemorrhoids. Sixty or 70 grains of the scraped root, macerated for about 5 minutes in a quart of water, may be taken in the course of 24 hours, repeating this quantity daily, as long as required. The dose of the fluid extract of the root is from 15 to 90 minims, in a glass of water, repeating the dose every 3 or 4 hours; specific piper methysticum, 5 to 30 minims.