Antidandruff compositions.

0001The present invention relates to compositions containing zinc pyridine thione as antimicrobial agent, and to their use in treating or preventing disorders of the skin and scalp.

0002Zinc pyridine thione is a well known antimicrobial agent which is commonly incorporated into antidandruff compositions such as hair shampoos and conditioners. Whilst these generally achieve an antidandruff action the performance of such compositions is less than ideal because the detergents present in the compositions tend to reduce deposition of the ZPT on the hair and scalp, and that which is deposited is swiftly washed off during rinsing.

0003It has now been surprisingly found that, by selecting certain sizes of ZPT particles, formulations can be produced having improved antidandruff action. Moreover such ZPT formulations may be used in the treatment of various flaking and scaling skin disorders and other microbial conditions.

0004Accordingly, the present invention provides a hair or skin-care composition comprising zinc pyridine thione in association with a conventional carrier, characterised in that a major proportion of the zinc pyridine thione is in the form of particles each having a maximum diameter of 2 µm, and a maximum volume of 3 x 10-¹⁷ m³ and a minimum surface area of 2 m²/g, and being substantially in the form of hexagonal flat platelets or fragments thereof.

0005Compositions containing ZPT as desciibed above have the advantages that the ZPT covers tie hair and scalp and skin more efficiently, it is less readily removed during rinsing and has improved antidandruff activity.

0006Also, as the particles of ZPT are small and have a large surface area, they will be more rapidly solubilised in/on the scalp by either sebim or water, and hence be more effective than the standard larger particles during use.

0007Examples of the conditions which can be effectively alleviated are: dandruff, seberrheic dermatitis, tinea infections and "dry" fl:king skin or winter xerosis.

0008Preferably at least 75% of the ZPT i. the composition is in the form of particles as described above, more preferably at least 85% and most preferably at least 90%.

0009It will be appreciated that such particles may be produced by various procedures including crystallisation and that the particles will not all be in the form of perfect hexagonal platelets but many will be broken, agglomerated or incomplete.

0010Preferably the major proportion of ZPT particles have a maximum diameter of 1 pm.

0011Preferably the major proportion of the ZPT particles have a maximum volume of 4 x 10-1⁸ m3.

0012Preferably the major proportion of the ZPT particles have a minimum surface area of 4 m²/g.

0013The specified material may be presented in hair dressings, hair conditioners and shampoos. Other presentations of the composition include creams, ointments and lotions for treating facial, scalp and other superficial disorders.

0014Preferably compositions according to the present invention are presented as conventional hair shampoos or conditioners and include detergents such as sodium lauryl ether sulphate, sodium n-lauroyl sarcosinate, ammonium alkyl sulphide, and other conventional ingredients including thickeners, opacifiers, colourants, perfumes and preservatives.

0015Suitably the compositions according to the present invention are shampoos or conditioners, for instance as described in European Patent Application Nos 0 007 704 and 82300398 and U.K. Patent Application No. 8132141.

0016The size and shape of the the ZPT particles in a composition can be ascertained by conventional techniques such as Electron Microscopy, Coulter Counter or Centrifugal Particle Size Analysis.

0017Conveniently it may be ascertained by electron- microscopy.

0018Particles of ZPT for use in the compositions according to the present invention may be produced for instance by crystallisation of the zinc salt from solution of the more soluble sodium salt of pyridine thione. Alternatively they may be obtained from ZPT containing particles of all sizes by settling, optionally accelerated by centrifugation and selecting samples containing the appropriate distribution of particle sizes.

0019The present invention also provides a method for treating or preventing disorders of the skin and scalp which comprises applying a composition as hereinbefore defined to the hair, scalp and/or skin of the sufferer.

0020The invention will now be illustrated by the following Examples, which are not intended to limit the scope of the invention in any way.

Example 1

Production of ZPT fine platelets

00211 Mole of zinc sulphate (161 g) was dissolved in distilled water containing 1% sodiur lauryl ether sulphate. The solution was heated to 60°C.

00222 Moles of sodium pyrithione (299 g) was dissolved in water and heated in a separated container, also to 60°C.

0023The two solutions were mixed and rapidly cooled. The crystals of zinc pyrithione formed were filtered with a glass micro filter, washed and dried. Their particle size was measured.

0024The crystals were then suspended in a suitable suspending agent (e.g. a surfactant/magnesium silicate system) and centrifuged.

0025Centrifugation time, speed and motor angle are dependent on the viscosity and densi y of the solution and the density of zinc pyrithione p.rticles (spherical shape is assumed), as governed by Stokes' Law:<maths id="math0001" num=""><img file="EP0093541A2_D0001.tif" /></maths><ul id="ul0001" list-style="none"><li>D = diameter of sphere</li><li>η = viscosity of fluid</li><li>v = terminal velocity</li><li>ρs ₌ density of sphere</li><li>ρf = density of fluid</li><li>g = acceleration</li></ul>

0026After adequate centrifugation the supernatent was decanted, the crystals filtered and dried. Their particle size was remeasured, and if &lt; 2 µm they were stored in a dark container at 0°C.

Example 2

Formulations containing ZPT fine platelets

0027<tables id="tabl0001" num="0001"><img file="EP0093541A2_D0002.tif" /></tables>

0028from Example 1 Sodium chloride, perfume, colour qs Water qs to 100

2) Cream Rinse

0029<tables id="tabl0002" num="0002"><img file="EP0093541A2_D0003.tif" /></tables>

3) Hair dressing

0030A water-in-oil emulsion is produced from the following ingredients: <tables id="tabl0003" num="0003"><img file="EP0093541A2_D0004.tif" /></tables>

4) Facial and/or Body Cream

0031<tables id="tabl0004" num="0004"><img file="EP0093541A2_D0005.tif" /></tables>

Biological Data

a) Antidandruff trial

0032A double blind clinical trial using human subjects, and a subjective technique to evaluate dandruff levels has shown smaller particle sized zinc pyrithione to be more effective at alleviating dandruff. After 6 weeks of treatment, volunteers in the group receiving the base shampoo showed no change in their dandruff level (8 volunteers). Subjects in the group receiving a 1% zinc pyrithione shampoo with an average particle size of 2.5 µm (high proportion <1 µm) showed a group mean percentage reduction in dandruff level: of 60% (9 volunteers). Subjects in the group receiving a 1% zinc pyrithione shampoo with an average particle size of 7 µm (high proportion > 1 µm) showed a group mean percentage reduction in dandruff levels of only 40% (9 volunteers).

b) Antimicrobial activity in vitro

0033Two ZPT fractions were prepared in aqueous suspension such that they differed in mean particle size and aspect ratio. The fractions consisted of one enriched in the small-particle ZPT hexagonal platelets described above and another consisting of relatively large-particle ZPT which had been depleted of the small-particle material by repeated centrifugation and washing. These fractions were assayed using the commonly accepted and most reputable in vitro test of anti-dandruff activity: antimicrobial activity against Pityosporum ovale via agar diffusion. Pityosporum ovale was grown on agar plates containing filter paper discs or wells into which the test suspensions (5 replicates) were introduced. Plates were incubated at 37°C and zones of inhibition of yeast growth were determined after 48 hours. At all concentrations of ZPT suspension tested in the range 0.03-0.61g%, small particle ZPT was found to yield larger zones of inhibition of yeast growth than did the large-particle material.