PEDALIACEAE

The Pedaliaceae or pedalium family contains about 16 genera of annual or perennial plants native to the tropics and subtropics.

• Leaves are opposite, the upper leaves sometimes alternate; simple or deeply lobed and covered with slime-secreting hairs or glands
• Flowers are bisexual, irregular, axillary and usually solitary
• Calyx 5-parted, corolla 5-lobed and broadly tubular, stamens usually 4 in 2 pairs borne on the corolla tube
• Fruit a nut or capsule, often hooked or horned

Sesamum is the best known member of the family.

Harpagophytum procumbens

Devil's claw

Description

A perennial growing up from large globular tubers. Flowers trumpet shaped, red or violet coloured. Fruit large, hooked claw-like.

Family Pedaliaceae

Habitat and cultivation

Native to eastern and southern Africa, in the desert mainly around Namibia, South Africa and Botswana. It does not grow in other places.

Parts used

The secondary tuberous roots.

Active constituents

1) Iridoid glycosides including harpagoside (about 2%), harpagide and 8-O-p-coumaroylharpagide1–3

2) Phenylpropanoids including acteoside

3) Sugars—mainly tetrasaccharides4,5

In smaller amounts:

4) Terpenes mainly diterpenes¹ but also triterpenes—ursolic and oleanolic acids⁶

5) Aromatic acids including cinnamic,¹ caffeic⁷ and chlorogenic acids⁶

6) Phytosterols including β-sitosterol and stigmasterol⁶

7) Flavonoids derived from luteolin and kaempferol⁶

8) Harpagoquinone⁶

Nutritional constituents

Minerals: Phosphorus, potassium, calcium, manganese, iron, copper and zinc

Actions

1) Anti-inflammatory

2) Analgesic

3) Diuretic

4) Sedative

5) Antirheumatic

Scientific information

Harpagophytum reached Europe in the early 20th century and since then its use has grown, particularly in Germany, for the treatment of joint pain. Such was the demand that the roots were becoming endangered and efforts are now being made to cultivate the herb commercially.⁸ There are two species of Harpagophytum, H. procumbens and H. zeyheri, that have been used in southern Africa for medicinal purposes. They have similar chemical constituents and pharmacological properties but are distinguishable by their iridoid profiles but commercial preparations probably consist of both species.⁹ It is approved by German Commission E for loss of appetite, dyspepsia and musculoskeletal degenerative problems.

Harpagophytum was traditionally used to treat joint inflammation and has been investigated in this context. The active constituents responsible and mechanism of action have not been fully established although harpagoside level is used as a marker for the strength of the herb.

Musculoskeletal

In vitro—Devil's claw modulates a number of different cytokines and this may be one of the mechanisms by which it is able to reduce inflammation.^10–13 Harpagoside itself can inhibit both 5-LOX and COX-2^14,15 however ex vivo studies indicate it is not the only constituent contributing to an anti-inflammatory activity, the whole extract being stronger than harpagoside alone.¹²

In vivo—The herb has been effective in the treatment of pain associated with various joints including:-

• low back pain of a chronic and non-specific nature^16,17 and not due to spinal nerve irritation.¹⁸ It gave much the same relief as the anti-inflammatory rofexcoxib¹⁹
• arthroses of hip and knee—signs and symptoms measurably reduced²⁰
• arthritis of hip and knee¹⁶—comparable in efficacy and with fewer side effects than diacerhein^21,22 and required less concurrent analgesia²²
• slight to moderate pain of back, neck and shoulders of non-specific nature, reduced muscle stiffness²³

It also improved mobility and reduced pain in degenerative rheumatism.²⁴ However a small trial using arthritic patients unresponsive to pharmaceutical therapy found no improvement on introducing an aqueous based tablet of the herb.²⁵

Healthy people who took the herb for 3 weeks had no change in arachidonic acid metabolism, an effect that occurs with non-steroidal anti-inflammatory drugs.²⁶

There are a number of reviews of clinical trials where Harpagophytum was used to treat osteoarthritis and chronic low back pain and the evidence strongly supports its effectiveness at doses of 50 mg harpagoside or more a day.^6,27,28 Reviewers have been critical of the quality of many of these trials and they conclude better research is necessary before drawing firm conclusions.^29,30

Other

In vitro—The herb is inhibitory to a number of micro-organisms particularly aerobic bacteria including Staphylococcus aureus and also to Candida spp.31 Diterpenes show strong anti-plasmodial activity (effective against a chloroquine-resistant strain of Plasmodium falciparum) whilst having no cytotoxicity to human cells.³²

Water soluble components of Harpagophytum³³ and the whole herb³⁴ are strongly anti-oxidant due at least in part to the phenols, harpagoside being only weakly so. The herb has potential to treat inflammatory bowel disease.³⁴

Devil's claw is used in some parts of South Africa to treat type 2 diabetes.

Medicinal uses

Gastro-intestinal tract

The iridoid fraction is bitter and therefore stimulates digestive secretions.

• dyspepsia
• anorexia

Musculoskeletal

The actions make it particularly effective in the treatment of problems in this system:

• arthritis
• rheumatism
• fibrositis
• myalgia
• painful arthrosis
• lumbago
• tendonitis
• pleurodynia
• gout

BHP specific for rheumatic disease.

Pharmacy

Three times daily
For dyspepsia and anorexia
Decoction	–   0.5 g or as dried tuber
Tincture 1:5 (25%)	–   1 ml
Other applications
Decoction	–   1.5–2.5 g or as dried tuber
Tincture 1:5 (25%)	–   2.0–4 ml
Fluid Extract (25%)	–   1.0–2 ml

Dosage recommendations differ slightly from one study group to another as do commercial preparations. Most commercial processing increases the proportion of harpagoside.

ESCOP's recommended dosage is 2–5 g daily rising to 4.5–9 g for low back pain. Chrubasik, who has contributed many papers on the subject, suggests that a minimum daily dose of 50 mg of harpagoside is required for effective pain relief^35,36 and that even though the iridoids are equally soluble in water and alcohol, water extracts may be more effective based on the results of clinical trials.³⁷ Interestingly doubling the dose of harpagoside from 50 mg to 100 mg did not give greater relief of back pain.¹⁷ ESCOP recommends treatment with the herb be continued for 2–3 months to achieve results.¹⁹

Pharmacokinetics

Studies show harpagoside reaches peak plasma levels 1.3 to 2.5 hours after ingesting whole extracts.¹² In vitro, bacterial flora metabolised the iridoids, converting them into the alkaloid aucubinine B.³⁸

Precautions and/or safety

Many of the clinical trials report good tolerability with few side effects using the equivalent of 3 ml per day of a 1:2 extract or 60 mg of harpagoside,^16,23,24 even after one year's continuous use.¹⁹

Care should be taken with patients who have peptic ulceration—due to the stimulation of digestive secretions. Minor gastro-intestinal side effects have been noted including diarrheoa.^17,21

Interactions

In vitro a commercial extract inhibited some cytochrome P450 isozymes.³⁹ In vivo there are no reports of any interactions although there is one anecdotal report of purpura in a patient taking warfarin and Harpagophytum concomitantly.⁴⁰

Historical uses

Fevers, blood diseases including malaria, digestive disorders, allergies, skin problems including cancer; complications of pregnancy.