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University of the Western Cape (2013)

Development and characterization of a transdermal formula for an extract of the medicinal plant harpagophytum procumbens

Ebrahim, Naushaad

Titre : Development and characterization of a transdermal formula for an extract of the medicinal plant harpagophytum procumbens

Auteur : Ebrahim, Naushaad

Université de soutenance : University of the Western Cape

Grade : Philosophiae Doctor – PhD 2013

Résumé partiel
The skin is the largest and most readily accessible organ of the body. The stratum corneum forms the outermost layer of the skin, which functions as a barrier to the external environment and regulates the passage of molecules across the skin. Drug delivery across the skin offers advantages over other routes of administration, bypassing the hepatic first pass metabolism, maintaining therapeutically effective drug levels, and improved patient compliance. Currently, there is a strong trend in the use of plant materials and extracts for medicinal purposes. Devil’s Claw (Harpagophytum procumbens) is a medicinal plant located in many regions throughout Southern and South Africa. It is used for its anti-inflammatory and analgesic properties with the harpagoside and harpagide components present reported to be responsible for these properties. Its activity has been reported to be as a result of the direct and indirect inhibition of Cyclooxygenase- 2 enzyme (COX-2). Efforts to improve the permeation of synthetic conventional compounds are constantly investigated, and great improvements of these formulations have led to very effective formulation of transdermal dosage forms such as anti-inflammatory drugs. The same should be possible for medicinal plants. Optimal permeation across the skin requires a drug to possess lipophilic as well as hydrophilic properties. Research suggests that a drug should have an aqueous solubility of more than 1 mg/ml and an octanol-water partition coefficient (log P) between 1 and 2 to optimally penetrate the skin (higher values indicating increased lipophilicity). Compounds not possessing these characteristics may be facilitated across the skin by the introduction of permeation enhancers in the formulation that include Azone® and sodium dodecyl sulphate xvi (SDS). The main aims of this study were to make an extract of Harpagophytum procumbens and to determine the direct COX-2 inhibition activity of this extract and further to formulate this extract into a pharmaceutical gel, with permeation enhancers that maintains its COX-2 enzyme inhibition qualities after transdermal penetration. The analytical techniques verified the existence of a harpagide and harpagoside components in the crude Harpagophytum procumbens extract and they were quantified in the extract at 3% and 1% respectively. COX-2 inhibition by the Harpagophytum procumbens extract was determined by a direct enzyme inhibition study and quantified by means of measuring the production of the product formed by the enzyme over a time interval in the presence of excess enzyme substrate. Crude Harpagophytum procumbens extract demonstrated a greater COX-2 enzyme inhibition than pure harpagide and harpagoside individually and combined. This indicated the existence of compounds in the extract contributing to this synergistic effect. This was reflected in the IC50 values indicating that the Harpagophytum procumbens crude extract had the lowest IC50 values concentration when compared to the harpagide and harpagoside. Octanol-PBS partition coefficient (log D) experiments were performed with various permeation enhancers and gels with varying combinations in order to determine the changing partitioning properties of harpagide and harpagoside.

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