PHARMACEUTICAL COMPOSITION FOR TOPICAL APPLICATION

Abstract: Compositions for topical application useful for preventing pressure sores comprise a slow-acting nicotinate ester, e.g. hexyl nicotinate, in a concentration and formulation insufficient to cause observable erythema but sufficient to promote peripheral blood flow. The composition may also comprise usual ingredients in compositions for topical application to the skin.

Description: This invention relates to pharmaceutical compositions for topical application, and provides a novel composition useful for preventing bed sores. Patients who are unable for any reason to move themselves frequently suffer from so called "bed sores", more properly pressure sores, which are local areas of ulceration caused by prolonged pressure preventing an adequate blood supply to that area. It is known to use nicotinate esters, e.g. methyl nicotinate, in compositions for topical application to the skin to produce pronounced local erythema. In such compositions, the nicotinate is normally used in a concentration of, for example, l to 2.5%. Such erythema causes a local sensation of warmth which is useful in alleviating certain types of local pain usually muscular origin. The generation of pronounced and perhaps persistent erythema in an area prone to a pressure sore would, however, be inappropriate since that would tend to exacerbate the problem. It has now unexpectedly been discovered that nicotinate esters can be used to improve local blood supply to the skin without causing obvious erythema. This has been demonstrated by the tests described below. The consequence of this discovery is that is is possible to produce a composition which may be used to increase blood flow in areas affected by pressure sores without inducing local irritation. The local restriction in blood flow caused by the pressure is thereby alleviated and this substantially prevents the formation of a pressure sore. The present invention accordingly provides a pharmaceutical composition for topical application to skin areas prone to pressure sores, comprising a slow-acting nicotinate ester in a concentration sufficient to improve local blood flow (i.e. increased blood cell flux) in an epidermal area without causing obvious erythema, associated with an appropriate vehicle. The nicotinate ester must be "slow-acting", i.e. it should not produce a too rapid and transient effect as it is desirable to reduce the frequency of application of the composition to avoid the inconvenience associated with frequent application. Rapidity of action is related to speed of absorption which depends on molecular size and oil/water solubility. Smaller molecules and those with an oil:water partition coefficient of about l:l are absorbed most efficiently. In order to slow down the rate of absorption it is necessary to increase the size of the molecule, and this may alter the solubility characteristics of the molecule in one of two ways, each of which can slow down penetration for the following reasons: (l) If the molecule becomes more lipid soluble, a depot of the ester is formed in the stratum corneum from which it is only slowly released into the more aqueous environment of the viable epidermis; (2) If the molecule becomes more water soluble, the ester tends to remain longer in the formulation and is only slowly released into the stratum corneum. Methyl nicotinate, for example, is a small molecule with an oil:water partition coefficient of about l:l. It therefore acts very rapidly and is unsuitable for use in the present invention. Hexyl nicotinate is an appropriate ester with more lipid and less water solubility but other suitable nicotinates could also be used. It is a simple matter to test nicotinate esters for their potential utility in the present invention. As already mentioned, known nicotinate-containing compositions often contain l% or more of a nicotinate ester. This is substantially more than the proportion required in the present invention. While appropriate concentrations can easily be found by routine experiment using the technique described below, in the case of hexyl nicotinate, an appropriate concentration range is 0.025 to 0.2% by weight of the composition. Concentrations in the range 0.l to 0.2% cause erytheme in a significant proportion of patients, and it is therefore preferred to use only about 0.025 to 0.075% by weight of hexyl nicotinate based on the weight of the composition. The composition is preferably made up in the form of a lotion for ease of application. For this purpose the vehicle for the nicotinate ester may be a combination of stearic acid in a proportion of 2 to 8%, for example 3 to 8%, by weight of the composition, cetostearyl alcohol in a proportion of 3 to 6% by weight of the composition, and water. These proportions give a lotion, i.e. a composition which can be poured. If a cream is desired, the proportions of stearic acid and cetostearyl alcohol may be appropriately increased, e.g. up to about l0% by weight in each case. Preferably, the compositions in accordance with the invention contain other ingredients. Thus, it is desirable to include a zinc supplement, e.g. a zinc soap such as zinc stearate, in the composition to promote healthy skin growth. An appropriate concentration is 0.5 to 2% by weight of the composition. It is desirable to include a bactericide to protect against microbiological contamination. A cationic bactericide such as cetrimide is included as this has the added advantage that it is an emulsifier which promotes the homogeneity and stability of the composition. It may be present in a concentration of 0.5 to 2% by weight of the composition. Chlorocresol in a concentration of 0.05 to 0.2% by weight may be for additional preservation. To provide the treated area of skin with further protection, it may be advantageous to include in the compositions of the invention an oil soluble polysiloxane such as that sold under the trade mark Dimethicone. Such a silicone forms non-volatile barrier film on the treated area of skin which assists in keeping out infection and reducing local evaporation and thus drying out of the skin. Further, since areas prone to pressure sores are frequently areas subject to friction, it may be advantageous to include a lubricant in the new compositions. Appropriate lubricants are lower alkyl esters of long chain fatty acids of, for example, l2 to l8 carbon atoms, such as isopropyl myristate. The silicone and the lubricant may be present in a concentration of 5 to l0% and 5 to l5% by weight of the composition respectively. The upper limit on the lubricant concentration may be l0% by weight. Other conventional ingredients in compositions for topical application may also be included, e.g. glycerol in a concentration of 0.5 to 5% by weight of the composition. The new compositions may be made by dissolving the water-soluble ingredients, e.g. the bactericide, in purified water, which has, if necessary, previously been heated to remove dissolved air at a temperature of preferably 80-l00°C. The oily constituents of the vehicle are separately heated, preferably to 80-l00°C, and the oleophilic constituents of the composition are thoroughly mixed in. The aqueous and oily constituents are then combined and homogenized, preferably at 50-60°C. The nicotinate ester is then added, preferably at 40-50°C, and finally the composition is filled into sterile containers. The effect of the compositions in accordance with the invention in promoting local blood flow has been demonstrated using a laser Doppler flowmeter (see "Laser Doppler Measurement of Cutaneous Blood Flow" G.A. Holloway and D.W. Watkins, Journal of Investigative Dermatology 69 , 306-309, (l977). This flowmeter is used to shine laser-produced red light into the area of skin under study before and after treatment. Any increase in the rate of flow on the red blood cells in the illuminated areas produces a difference in the Doppler effect shown by the reflected light, since reflections from essentially stationary surfaces can be differentiated by this means from reflections from moving red blood cells. The blood cell flux is then given by the product of the number of red blood cells found to be moving in the irradiated volume of skin and adjacent tissue and the mean red blood cell velocity. The results expressed by the flowmeter indicate the relative change of the blood cell flux over control conditions, i.e. before application of the composition. The following table shows the results obtained using the composition of Example l below on ten subjects: Using an erythema scale of 0 to 3, an erythema value of up to 0.5 (which is barely detectable) is considered acceptable. The figures for "area" given in the third column are obtained by graphical integration of a graph of blood cell flux against time obtained using the laser Doppler flowmeter. Any figure in this column greater than about 20 may be regarded as indicative of a useful improvement in local blood flow in the treated area. The table clearly shows that such an improvement can readily be obtained with a degree of erythema of 0.5 or less. Thus the compositions in accordance with the invention make it possible to obtain a useful increase in local blood flow without appreciable erythema. The compositions of the present invention are thus useful in preventing pressure sores where is it desired to stimulate local blood flow without obvious erythema. An increased local blood flow following application of the composition in accordance with the present invention is observable for typically l0 to 90 minutes after the application. Since continuous improved blood flow is not required for prevention of pressure sores, application twice or three times a day is sufficient. The following Examples illustrate compositions according to the invention. Example l A composition was formulated containing (% by weight): This composition 0.05% hexyl nicotinate, the most preferred amount. The other compositions used in the test contained the amounts of hexyl nicotinate specified in the table given above, an appropriate adjustment being made in the amount of water. Example 2 A composition was formulated containing (% by weight): This composition has the advantage of being less viscous than that of Example l. The compositions of Examples l and 2 (and other compositions of the invention may be manufactured as follows: (a) The purified water is heated preferably to 80-l00°C to remove dissolved air. The cetrimide, glyceroland chlorocresol (i.e. the water-soluble ingredients) are added with stirring until completely dissolved. (b) The aqueous solution obtained is allowed to cool to 50-60°C, preferably 55°C. (c) The stearic acid, cetostearyl alcohol, dimethicone 350, isopropyl myristate and zinc stearate (i.e. the oily vehicle ingredients and the other oleophilic ingredients) are mixed together by warming to 60-l00°C, preferably 60°C and allowed to cool to 50-60°C, preferably 55°C. (d) The aqueous phase from step (b) is added to the oily phase from step (c) and the mixture emulsified by homogenisation to produce a smooth lotion. The emulsion is then allowed to cool. (e) The hexyl nicotinate is added to the product step (d) at 40-50°C, preferably 50°C, and mixed in thoroughly. (f) When the lotion obtained has cooled to 37-43°C, preferably 40°C, it is filled into 350 ml round high density polyethylene bottles or other suitable sterile containers, preferably sealed with a pump dispenser principally constructed of high density polyethylene or other suitable material.

Claims: 1. A pharmaceutical composition for topical application comprising a slow-acting nicotinate ester in a concentration sufficient to cause increased blood cell flux in an epidermal area to which the same composition is applied, but insufficient to cause erythema, and an appropriate vehicle. 2. A composition according to claim l in which the nicotinate ester is hexyl nicotinate. 3. A composition according to claim l or 2 in which the said nicotinate ester is present in a concentration from 0.025 to 0.075% by weight based on the weight of the composition. 4. A composition according to any one of claims l to 3 which also contain a zinc supplement. 5. A composition according to claim 4 in which the zinc supplement is present in a concentration of 0.5 to 2% by weight based on the weight of the composition. 6. A composition according to any of claims l to 5 in which the vehicle comprises stearic acid, cetostearyl alcohol and water. 7. A composition according to claim 6 in which the vehicle comprises 2 to l0% by weight of stearic acid and 2 to l0% by weight of cetostearyl alcohol, based on the total weight of the composition, the balance of the composition being water. 8. A composition according to any one of claims l to 7 which also contains one or more of a cationic bactericide, an oil soluble polysiloxane, and a lubricant. 9. A composition according to claim 8 which contains 0.5 to 2% of cetrimide as cationic bactericide, 5 to l0% of an oil polysiloxane, and 5 to l5% of isopropyl myristate, the said percentages being by weight based on the total weight of the composition. l0. Use of hexyl nicotinate or other slow-acting nicotinate ester in the preparation of a pharmaceutical composition for use in therapy to promote peripheral blood flow without causing observable erythema.

Inventors: WHITEFIELD, MARTIN
Applicants: DIOMED DEVELOPMENTS LIMITED
Application year: 1986
Main classification: A61K31
IPC codes: A61K31, A61K9, A61K47