Related species include rough comfrey, S. asperum Lepech, and Russian comfrey, Symphytum × uplandicum Nyman (a hybrid of S. officinale × S. asperum). Boraginaceae Boneset; knitbone Symphyti radix; Symphyti herba Root, aerial parts Mucilage polysaccharides (29%) composed of fructose and glucose units, especially in the root; allantoin, phenolic acids, including rosmarinic, chlorogenic, caffeic and α-hydroxy caffeic acids; glycopeptides and amino acids; triterpene saponins, as monodesmosidic and bidesmosidic glycosides based on hederagenin, oleanolic acid and lithospermic acid. Comfrey also contains PAs, the content of which depends on the source of plant material and storage conditions (the alkaloids are labile). The PAs include intermedine, lycopsamine, symphytine, 7-acetylintermedine and 7-acetyllycopsamine (Staiger 2012). Symphytum species vary in alkaloid content, with Russian comfrey containing a higher proportion of the more toxic retronecine diester form than S. officinale (Rode 2002). There is increasing clinical evidence to support the effectiveness of comfrey root extract ointment in the treatment of various musculoskeletal and joint complaints, as highlighted in the subsequent section. In a placebo-controlled, double-blind, randomised clinical trial of 120 patients with acute upper or lower back pain, a proprietary comfrey cream (Kytta-Salbe®) containing comfrey root fluid extract (1:2, 35.0 g, extraction solvent ethanol 60% v/v, <0.35 ppm pyrrolizidine content) was applied three times per day, 4 g per application, and compared to placebo over 5 days. Results showed a significant (p < 0.001) reduction in pain in the group treated with comfrey extract compared to placebo. The comfrey ointment was also found to be fast acting, with pain intensity reduced by about 33% after 1 hour (Gianetti et al. 2010). A double-blind, placebo-controlled, three-arm randomised trial (n = 379) assessed a combination of 35% comfrey root extract plus 1.2% methyl nicotinate, versus methyl nicotinate alone or placebo, applied topically three times daily for 5 days, for relief of acute upper or low back pain. Pain scores were found to be significantly lower (p < 0.0001) in the combination treatment group than in the methyl nicotinate alone or placebo groups, demonstrating superiority of the combination treatment (Pabst et al. 2013). The proprietary ointment Kytta-Salbe was assessed in the treatment of osteoarthritis in a randomised, double-blind, placebo-controlled trial of 220 patients suffering from painful osteoarthritis of the knee. Patients were administered 2 g of either the comfrey cream or placebo three times daily for 21 days. The comfrey treated group had significant (p < 0.001) reduction in pain and improvement in quality of life, mobility of the knee, and clinical global assessment measured by both physicians and patients (Grube et al. 2007).
Comfrey
Symphytum officinale L.
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