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Feverfew is available as a fresh leaf; dried, powdered leaf; capsules; tablets; fluid extract; dry standardized extract; crystals; and oral drops (4). Brand names include Migracare® (600 ^g of parthenolide per capsule), Migracin® (feverfew extract 1:4 and white willow bark), MigraSpray®, MygraFew®, Lomigran, 125-mg Migrelief® (light green round tablet containing 600 ^g of parthenolide), Partenelle, Phytofeverfew, and 125-mg Tanacet® (not <0.2% parthenolide). Feverfew contains flavonoid glycosides and sesquiterpene lactones. Parthenolide can constitute up to 85% of the sesquiterpene lactones in feverfew grown in Europe (1,4), but is present in lesser amounts or is even totally absent from North American feverfew (4). Parthenolide is concentrated in the flowers and leaves, as opposed to stems and roots, and parthenolide content of the leaves may decrease during storage (4,5). The vegetative cycle also influences parthenolide content (4). Although parthenolide is thought to be the active ingredient in feverfew, and preparations are often standardized based on parthenolide content (6), there may be other active compounds, including the lipophilic flavonol tanetin, other methyl monoterpene ethers, and chrysanthenyl acetate, monoterpene (4).

Most tablet and capsule formulations contain 300 mg of feverfew, and the recommended dose is usually two to six tablets or capsules per day. A dose of 250 ^g of parthenolide is considered an adequate daily dose, and 0.2% parthnolide is considered the acceptable minimum parthenolide concentration; therefore, the manufacturer's recommended dose is probably in excess of what is considered therapeutic (6). In the prevention of migraine headache, doses used in studies have been 50-100 mg of dried feverfew leaves daily (7-9) (60 mg of dried feverfew leaves = 2.5 leaves) (4). However, the parthenolide content of the North American plant is low (6), and parthenolide content in feverfew products varies widely (5), and may be lower than stated on the label (10) or even absent from some preparations (5,10). For example, no parthenolide could be detected in two-thirds of feverfew products purchased in Louisiana health food stores (6). The parthenolide content of powdered feverfew leaves falls during storage (5). Given that the active ingredients of feverfew have yet to be definitively determined, it is difficult to designate a therapeutic or toxic dosage range. (See Subheading 5.1. for discussion of melatonin content of feverfew products).

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