Willow - Medicinal Uses, Interactions, Side Effects, Dosage
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<p><strong>Willow </strong></p>
<p>There are over 300 species of willow trees found mainly in Europe and North America. The species of medical interest include <em>Salix alba </em>(white willow), S. <em>nigra </em>(black willow), and S. <em>purpurea </em>(purple willow); however, S. <em>daphnoides </em>and S. <em>tragilis </em>along with S. <em>purpurea </em>provide the greatest yield of salicylate precursors. The willow is the source of acetylsalicylic acid (aspirin); indeed, this well-known drug is generically named for its phytomedicinal source. </p>
<p><strong>Uses and Benefits: </strong></p>
<p>In ancient Greece, willow bark was used for gout and for febrile and painful disorders. In 1763 the Reverend Edward Stone of Oxfordshire reported on its value in treating fevers. Subsequently, salicylic acid was prepared from salicin in willow bark, and eventually aspirin was synthesized in 1853. Salicylic acid is also obtained from the meadowsweet, <em>Spira ulmaria; </em>aspirin was named after this plants Used for a variety of traditional indications in the past (including gastritis, gonorrhea, and as an aphrodisiac and sedative), willow bark is now mainly used to treat rheumatic disorders, and is a common alternative to aspirin as an analgesic and antipyretic. Recently, willow bark has been introduced into weight loss preparations. </p>
<p><strong>Pharmacology:</strong></p>
<p>Willow bark contains 1.5-11 % phenolic glyco­sides, including salicortin and its hydrolysis product salicin, as well as variable quantities of salicylic acid esters and their deriva­tives. Other constituents include proanthocyanidins, catechins, and flavonoids (e.g., isoquercitin). Tannins are present in a con­centration as high as 20%. Salicin and salicortin are prodrugs which are split by intestinal flora into glucose and saligenin (salicyl alcohol), and both of these are well absorbed; saligenin is oxidized in the blood and liver to salicylic acid. 2 Since these chemical conversions take time, the effect of willow bark is slower in onset than that of aspirin. Furthermore, the amount of active drug in the popular S. <em>alba </em>is much lower than in other willows. Thus, relatively low blood levels of active salicylates are obtained after oral use of crude willow herb preparations. Only concentrated willow bark extracts can provide sufficient active drug to reach blood levels of clinical value, since 80 g or more of a typical crude willow bark prepara­tion would be needed to obtain 794 mg of salicin, which is the equivalent of 500 mg of aspirin.</p>
<p>A study of 10 healthy volunteers given 1.4 g of a specific willow bark product reported a maximum salicylic acid serum level of 9.8 m/L. This level is equivalent to what is attained with an oral dose of 40 mg of acetylsalicylic acid. Such a result suggests that other agents in willow bark may account for its anti-inflammatory effect. </p>
<p><strong>Clinical Trials:</strong></p>
<p>In spite of its long use, only a few controlled trials have been conducted with willow bark to support it as an analgesic or antipyretic. Collectively, these studies suggest that appropriate extracts may be beneficial for milder painful condi­tions. A recently published, randomized, double-blinded, and placebo-controlled study of patients with chronic low back pain showed a positive dose-dependent effect, with pain relief within 1 week in patients taking 1400 mg of willow bark extract (containing 240 mg salicin) per day.8 A 2-month, randomized, non-crossover study in patients with chronic arthritis pain showed a small but statistically significant improvement in symp­toms with a low-dosage combination willow bark formulation (Reumalex; containing 100 mg white willow bark extract, gua­iacum, black cohosh, sarsaparilla, and poplar bark) compared to placebo. An unpublished study is commented on in two reviews in which 78 inpatients in a German hospital were treated for 2 weeks for osteoarthritis of the hip or knee. This was a double­blind, placebo-controlled trial that used a daily dose of 1360 mg of coated tablets of willow bark extract, equivalent to 240 mg salicin. The pain index significantly improved on the herbal preparation compared to placebo (P < 0.05).5 A preceding pilot study had also shown the superiority of willow extract over placebo. </p>
<p><strong>Adverse Effects:</strong></p>
<p>In general, willow bark has been reported to be very well tolerated, with adverse effects-such as nausea, skin rashes, and wheezing-in less than 4% of patients. Typical doses of salicin do not irritate the stomach, and recommended doses of willow bark extracts contain small amounts of salicylate; willow bark is therefore far less likely to cause gastric damage, bleeding, and allergic reactions than aspirin. The high tannin content, rather than the salicylate components, is more likely to cause gastric disturbance. However, large doses of willow bark may have effects similar to those of aspirin. </p>
<p><strong>Side Effects and Interactions:</strong> </p>
<p>Salicin does not inhibit platelet aggregation, and is thus safer than aspirin with respect to interference with coagulation and interaction with anticoagulant medications. The use of willow in combination with other anti-inflammatory agents may theoretically increase the risk of gastric irritation, although this has not been described. </p>
<p><strong>Cautions:</strong></p>
<p>Willow bark should not be used in asthmatic subjects or other patients who develop allergic respiratory problems or rashes from salicylates, and a cautious approach should be adopted in patients who have had gastric complications or bleeding with aspirin. Although it is likely to be safe, it is advisable not to give it to children at risk of Reye's syndrome. The general precautions for aspirin should be taken when using willow products, although the bleeding risks are less with willow. Its safety has not been evaluated in pregnancy and in breast-feeding mothers.</p>
<p><strong>Preparations </strong><strong>& </strong><strong>Doses: </strong></p>
<p>Willow bark is available from various sources, which differ in their proportion of active components. Solid products and extracts, including alcoholic preparations and teas, are available, and are often incorporated in multiple-herb preparations. Topical products are also in use. The recommended adult daily dose by mouth is usually 60-120 mg of the salicin component, but 240 mg/day may be more reasonable based on controlled trials. The usual dose of dried willow bark is 1.5-3 g given three to five times a day. Willow bark extract may contain as much as 17% salicin, but the amount is closer to 1% in some specimens ; thus correlation of bark dosages with salicin doses is unreliable. Standardized products with the amount of salicin listed on the label are recommended. </p>
<p><strong>Summary Evaluation:</strong> </p>
<p>Willow bark, which contains the analgesic salicin, is safer than aspirin, but effective dosing may be difficult to attain, and many experts are dubious about its value. Nevertheless, products are promoted for use in treating fever, pain, and inflammatory joint disease. Several controlled trials have demonstrated benefits for extract products in the treatment of rheumatic and sculoskele­tal pain. There is no established basis for incorporating willow bark in composite products for weight control or in "diaphoretic" teas. Its value in topical therapy has not been established. Although some authorities believe that willow bark is urely of his­toric interest, the evidence of recent studies suggests that this may be a premature judgment. </p>
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