Capsaicin is an active principle of the plant Capsicum annum (Solanaceae L.). It is used in the topical preparations in concentration of 0.025 to 0.075% as counter-irritant. Clinical research reaffirmed topical use of capsaicin in the cases of polyneuropathy, rheumatoid arthritis, diabetic and postherpetic neuropathy. Topically applied capsaicin demonstrates counter-irritant effect and produces heat, which leads to pain relief. Pain is the major symptom of neuralgia.
The aim of this study was to establish counter-irritant effect of capsaicin, which was incorporated in emulsion base O/W, gel and alcohol-water solution after preparations administered to the skin of healthy volunteers.
Capsaicin (Aldrich, USA) was incorporated in emulsion vehicle O/W, gel and alcohol-water solution in concentration of 0.025%. Affects of single applications of prepared preparations were researched preparations on peripheral circulation of the skin in the in vivo test. Equal amounts of preparations were applied to the inside forearm skin of 8 healthy volunteers. Temperature of the skin was measured before administration and 0.5, 1, 2, 4, 6 and 8 hours after application of cream, gel and solution with incorporated active principle. For temperature skin measure, Toff-guard INMT instrument was used (Organon Teknika, Belgie).
After preparations administration, increase of skin temperature was noted at the application spot. The cream caused the highest increase of the skin temperature (3 hours after cream application, the skin temperature increased for 1.5°C) but 3 hours after solution application, the skin temperature increased for 0.5°C was registered.
The irritants are drugs that act locally on the skin and mucous membranes to induce hyperemia, inflammation and, when the action is severe, visication. Certain irritants may be relatively selective for various tissues or cell types. Capsaicin is a naturally occurring substance derived from plants of the Solanaceae family with the chemical name trans-8- methyl-N-vanillyl-6-nonenamide (1).
Capsaicin is a counter - irritant used as a topical analgesic in painful conditions such as polyneuropathy, rheumatoid arthritis, diabetic and postherpetic neuropathy.
It induces the selective degeneration of the primary sensory efferent amyelinic neurons; in addition, capsaicin induces the release of substance P and inhibits its reuptake, which causes its complete depletion. Capsaicin application on the skin causes a burning sensation which turns into anesthesia by inhibition of neurotransmission by C fibbers (unmyelinated, of smaller diameter than A fibbers, transmit impulses for non- - discriminatory sensitivity). It does not affect the sensitivity to touch or heat. It does not alter the sensitivity of fibbers, which are responsible for finer discrimination (2).
In some country capsaicin - based magistral preparations are used; in other countries, proprietary products are available. Topical capsaicin has been introduced in the United States and Canada as a cream, gel or solution. Preparations contain 0.025 - 0.075% of capsaicin (3).
Materials
The following ingredients were used: Capsaicin (Aldrich, USA), White petrolatum, Polysorbate 60 (ICI UK), Carbomer (Carbopol 940) (B.F.Goodrich, USA), Ethanol (Zorka, Yugoslavia), Cetyl alcohol (Henkel, Germany), Liquid paraffine, Triethanolamine (Aldrich, USA), Methyl Parahydroxybenzoate, and Propyl Parahydroxibenzoate (Nipa, USA).
Preparation of cream
The emulsion base O/W was composed of Capsaicin (0.025%), White petrolatum, Cetylalchochol, Liquid paraffin, Polysorbate 60, Methyl Parahydroxybenzoate, Propyl Parahydroxybezoate and Water.
The emulsion system was made by adding slowly the aqueous phase (70°C) to the hot (70°C) oil phase containing emulsifier. The mixture was stirred using laboratory mixer at 1500 rpm. Capsaicin was added at 30°C.
Preparation of gel
The gel was composed of Capsaicin (0.025%), Carbomer (Carbopol 940), Liquid paraffin, Ethanol and Water.
Carbomer (Carbopol 940) was dispersioned in the mixture of Water and Liquid paraffin using laboratory mixer at 1500 rpm and Triethanolamine was incorporated using laboratory mixer at 100 rpm.
Preparation of alcohol - water solution
The alcohol - water solution was composed of Capsaicin (0.025%), Liquid paraffin, Ethanol and Water.
The alcohol - water solution was prepared by adding mixture of Capsaicin and Ethanol in the mixture of Liquid paraffin and Water using laboratory mixer at 500 rpm.
Temperature measurement
Affect of single applications of prepared preparations were researched preparations on peripheral circulation of the skin in the in vivo test. Equal amounts of preparations were applied to the inside forearm skin of 8 healthy volunteers. Temperature of the skin was measured before administration and 0.5, 1, 2, 3, 6 and 8 hours after application of cream, gel, and solution with incorporated active principle. For temperature skin measure, Toff - guard INMT (Organon Teknika, Belgie) instrument was used.
From the obtained results it was apparent that all preparations caused increased of the skin temperature. The highest increase of the skin temperature was noted after 3 hours from the application of all preparations. It was obvious that the cream caused the highest increase of the skin temperature (the skin temperature increased for 1.5°C). In the same time the gel caused increase of the skin temperature for 0.89°C. Moreover, 3 hours after alcohol - water solution application was registered the increase of the skin temperature for 0.5°C.
On the basis of the given results, it can be concluded that all prepared preparations in which was incorporated Capsaicin in concentration of 0.025% produced heat and the increase of the skin temperature what was confirmation of counter - irritant effect all prepared preparations.
Martindale (1995), The Extra Pharmacopoeia 31st Edition, The Pharmaceutical Press, London 638-640.
Bruneton J. (1999): Pharmacognosy Phytochemistry, Medicinal Plants, 2nd Edition, Tec&Doc, Paris 774-776.
Rumsfield J.A. et al. (1999): Topical capsaicin in dermatologic and peripheral pain disorders, The Annals of Pharmacotherapy 25, 381-388.