Herbal remedies for arthritis Willow bark

About three hundred different species of the genus Salix are called willow. The one that is generally recognized as a source of medicinal bark in the United States is Salix alba L., but for reasons that will become clear, the

bark of Salix purpurea L. and Salix fragilis L. are of superior quality. The principal active constituent of willow bark was long thought to

be a compound known as salicin, which chemically is salicyl alcohol gly- coside. However, recent studies have shown that a whole series of phenolic glycosides designated salicortin (normally the main active principle in willow species), fragilin, tremulacin, etc. is present in the bark, some in

much larger amounts than true salicin. 4 The glycosides, other than salicin, are relatively heat labile and are converted to the latter compound if the bark is dried at high temperature. 5 All of the phenolic glycosides have similar physiological effects, being prodrugs that are converted to the active principle, salicylic acid, in the intestinal tract and the liver. 6 Because of the time required for this conversion, the therapeutic properties of willow bark are expressed more slowly but continue to be effective for a lon-

ger time than if salicylate itself were administered. 7 Willow bark and its active constituents produce anti-inflammatory, analgesic, and antipyretic effects through their ability to inhibit cyclo-oxygenase and prostaglandin biosynthesis (see Figure 9.1 ).

For analytical purposes, the numerous phenolic glycosides are first converted to salicin and their content is then indicated as total salicin per unit weight of dried bark. Such studies show enormous variability, not only among different species of willow bark but also among different collec- tions of the same species. Barks of high quality, such as those of S. purpurea, range from about 6–8.5 percent total salicin; one sample of S. fragilis even exceeded 10 percent. Probably a figure of 7 percent for such quality barks is average. However, none of the S. alba samples exceeded 1 percent, and other willow species had even less. In Germany, a standard of not less than

1 percent total salicin has been established for willow bark. This is indica- tive of the low level of total salicin in most commercial samples. 8 Most of the willow bark available commercially is in the form of rather coarse pieces. Studies have shown that normal preparation of a tea from such material using hot water would extract only about 75 percent of the active principles. If a very finely powdered bark is used, the extraction will approach 100 percent of the activity.

The usual daily dose of aspirin for arthritic disorders is 3.6–5.4 g (average: 4.5 g) administered in divided doses. Equivalent amounts of other salicylates are also effective. The question then is concerned with how much total-salicin-containing willow bark must be administered to produce that amount of salicylate in the body. For purposes of this example,

170 Tyler's herbs of choice: The therapeutic use of phytomedicinals let us assume use of a relatively good-quality bark containing 7 percent

total salicin. Let us also assume that the bark is finely powdered and is carefully extracted with sufficient hot water to obtain 100 percent of the active principles. Because the exact composition of the mixture of phenolic glycosides (salicin, salicortin, etc.) varies in the individual barks, it is not possible to calculate the exact amount of active salicylate produced from a given quantity of an unknown mixture. Theoretically, it will be considerably less than 50 percent, and that conversion will occur over sev- eral hours rather than immediately. But for convenience in calculating, let us assume 50 percent.

Based on these generous assumptions, it would be necessary to con- sume the tea prepared from about 130 g of bark to yield an average daily dose of salicylate sufficient to treat arthritic–rheumatic disorders. At the standard strength of 1 teaspoonful per cup of water, that is more than 6 L (1½ gal) of willow tea daily. Considering the high concentration of tannin (8–20 percent) in the bark and the sheer volume of liquid involved, con- sumption of this quantity is not feasible. If ordinary willow bark with its approximately 1 percent total salicin were to be substituted for the superior bark, these figures must be multiplied by seven, yielding 2 lb of bark and some 11 gal of tea—an utterly impossible daily dose. The need for such high dosage levels also precludes effective use of the crude herb in another form, such as capsules or tablets.

What about the use of willow bark for other conditions—headache, fever, sprains, strains, etc.—that respond to treatment with salicylates? Here, there will likely be confusion about proper dosage because the German Commission E recommends use of a quantity of bark equivalent to 60–120 mg of total salicin daily. Such a minimal dose would have little therapeutic value and seems to be based more on the quantity of bark used to prepare a normal cup of tea than upon any proven value of the small amount of total salicin contained therein. It does also point out that willow bark is used in German medicine as an adjuvant or auxiliary drug, rather than as an agent that in itself possesses great therapeutic value. In practice, it is supplemented by administration of synthetic salicylates. 7,9

Side effects have not been reported with the use of willow bark tea, with the exception of gastrointestinal upset caused by the tannins present (not salicin). Precautions associated with salicylate therapy, such as hypersensitivity, are also applicable to willow bark; however, apparently because of the small amount of salicin present in the herbal tea, problems with side effects appear to be slight. 10

The National Formulary VI listed the average dose of salicin as 1 g. 11 This is a reasonable analgesic–antipyretic dose, considering that the compound has less than half the activity of salicylates. It would require approximately 14 g (1/2 oz or 3 heaping teaspoonfuls) of high-quality willow bark (7 percent total salicin) prepared as three cups of tea to yield a single

Chapter nine: Arthritic and musculoskeletal disorders 171 average dose of salicin. If ordinary white willow bark were employed,

these quantities would have to be multiplied by seven. In spite of the presence in various willow barks of total salicin—a mixture of therapeutically useful salicylate precursors—these herbs, by themselves, do not constitute effective treatment for arthritis or even for headaches, fevers, or muscle pains. The quantity of active principles present in even the highest-quality barks is insufficient to allow them to be consumed in sufficient amounts to constitute useful medicines. They may play a psychologically supportive role as auxiliaries to synthetic salicylate therapy in certain patients.

Feverfew It has been claimed that people in the United Kingdom self-medicate with feverfew more for arthritis than for migraine 12 ; however, the single clinical trial in rheumatoid arthritis failed to show any beneficial effect in forty women treated with 70–86 mg of dried feverfew leaf or placebo for

six weeks. 13 Notwithstanding, it has been suggested that feverfew may well be of benefit in milder cases of arthritis than that which afflicted the women in this trial, who were extremely refractory cases unrespon-

sive to all conventional drugs. 14 The authors of this failed trial have suggested, particularly, that feverfew may be of benefit in osteoarthritis and soft tissue lesions, for which self-treatment with feverfew is probably most common. 15

Herbal remedies for arthritis Willow bark