Effectiveness of devil's claw for osteoarthritis

Extract

Sir, The recently published systematic review on complementary therapies for osteoarthritis [1] dealt primarily with arthritis of the hip and knee. Although some studies with mixed arthritic patterns were included, studies restricted to low back pain were specifically excluded. Two randomized placebo‐controlled trials were cited concerning the effeciveness of Harpagophytum procumbens. Both investigated the effect of pulverized plant material containing 1.5 and 3% iridoid glycosides, and were no more than exploratory; one had no statistical calculation and the other no hypothesis. A recent definitive study [2] was not considered. It was designed with 90% power to detect a small difference [10 mm on a 100‐mm visual analogue score (VAS) scale, with a background standard deviation of ∼22 mm] between freeze‐dried Harpagophytum and the weak non‐steroidal anti‐inflammatory drug (NSAID) diacerrhein for hip or knee pain. After 4 months, no statistically significant difference was found between the two treatments. The study showed that freeze‐dried root tubers of Harpagophytum at a dose containing 60 mg harpagoside per day was as effective as, and had fewer side‐effects than, diacerrhein. Table 1 summarizes the types of controlled clinical studies with various Harpagophytum preparations that have been published in peer‐reviewed journals [2–7]. The results of these studies demonstrate that Harpagophytum extracts with >50 mg harpagoside per day are helpful in alleviating pain. According to the ESCOP monograph [8], up to 9 g of crude drug with not less than 1% harpagoside is recommended for painful arthrosis and tendinitis—a dose that contains up to 90 mg of harpagoside. This marker is unlikely to be the only or even the most important active principle of the drug, but may contribute to its overall clinical effect. Although the higher concentrations of harpagoside that are found in volunteers' blood soon after ingestion of a dose of extract are associated with more in vitro inhibition of lipoxygenase than the lower concentrations in later samples [9], no such association has yet been demonstrated for therapeutic effect (e.g. pain relief, decrease in joint swelling). Stimulated release of inflammatory mediators (prostaglandin E2, cytokines) from human monocytes is not affected by harpagoside [10] and is a more appropriate test procedure for inflammation than treatment of whole blood with a compound that increases the calcium permeability of any cell [9]. More research is needed to investigate the contribution of the iridoid glycosides to the total effect.