FIELD OF THE INVENTION
The present invention relates to zinc pyrithione containing personal care formulations.
More particularly, the invention relates to aqueous transparent solution of zinc pyrithione
at pH 5.5 - 8.5 having high anti-fungal activity.
BACKGROUND AND THE PRIOR ART
Zinc pyrithione (ZPTO), also known as zinc pyridine-2-thiol-N-oxide or bis [1-hydroxy-
2(H) pyridinethionato]-zinc is a broad spectrum antimicrobial agent and preservative in
metalworking fluids, plastics, paints, adhesives and cosmetics. ZPTO is insoluble in
water. Insoluble particulate zinc pyrithione has perhaps the most acknowledged efficacy
as an anti-dandruff agent owing to its anti-fungal activity. However being insoluble in
water, when used in personal care formulations, especially in shampoo as antifungal
agents, it produces white suspension that precipitate in the packaging bottle, when used
in shampoo as antifungal agent. Recommended usage level of ZPTO is 1 -2 % because
of its insolubility. But is perceived harsh by the consumers (US 2006 0182696 A1).
Solubility of ZPTO determines its effectiveness. In addition delivery of ZPTO from solid
particle depends on the size and shape. The antifungal and anti microbial activity of
ZPTO depends on the bioavailability of aqueous intact ZPTO molecule. As the solubility
of ZPTO in aqueous solution is very low (6-12 ppm), availability of ZPTO molecule in
aqueous solution is also low. Therefore to overcome these disadvantages (precipitations
and low water solubility of ZPTO) ZPTO is generally used in excess (1-2%).
It has been suggested that cationic polymers can increase the efficacy of zinc pyrithione
in anti dandruff shampoos by enhancing the deposition and retention of the water
insoluble ZPTO particles on scalp. US 3,489,686 teaches polyethylenimine or the
reaction product of polyethylenimine and ethylene oxide or propylene oxide; US
3,580,853 teaches cationic homopolymer comprising particulate cellulose derivative and
US 3,761,417 teaches piperidinum chloride which can increase the efficacy of ZPTO.
However US 2006 0182696 A1 clearly mentions the need for water soluble ZPTO, as it
tends to precipitate under storage from opaque formulations. The disclosure also
mentions the need of less irritating anti dandruff actives, which also means lower
concentration of the active.
In practice alcohol can be used for producing clear solution of ZPTO, but use of the
same in personal care formulations, especially in shampoo produce undesirable results.
Therefore the use of alcoholic suspension is only limited to anti-fungal/antimicrobial wipe
products. Therefore use of ZPTO in clear transparent shampoo is limited due to its
insolubility in water.
U.S. Pat. No. 3,940,482 teaches clear liquid composition of zinc pyrithione solubilized by
adding a polyethylenimine (quaternary ammonium compound) to a suspension of the
pyrithione complex in water for use as a bactericide or fungicide. However ZPTO
solubilized in alcohol/water using polyethylenimine (quaternary ammonium compound)
has a pH of about 9.0. Reducing pH to <8.0 leads to destabilization of mixture. It is
further known that ZPTO at alkaline pH (>8) is photo unstable.
Therefore, there is a need for effective anti-dandruff actives, which can effectively treat
dandruff at low concentrations, thereby having low degree of irritation (eye & skin); and
have superior physical characteristics that enable them to be easily formulated in hair
care products at a neutral pH.
OBJECTS OF THE INVENTION
It is one of the objects of the present invention to overcome the drawbacks of the prior
art.
It is another object of the present invention to provide soluble ZPTO at pH 5.5 -8.5, most
preferably 6.5-7.5 in aqueous medium without the use of any surfactants or a polymer,
and can be incorporated into formulations without any difficulty of stability or
precipitation.
It is yet another object of the present invention to provide 0.01 -10% solution of ZPTO,
which has increased antifungal efficacy.

It is yet another object of the present invention to provide clear ZPTO solution that can
be used in transparent hair care products, especially in antidandruff shampoo,
antidandruff hair gel, antidandruff hair soap, hair care serums, and conditioners.
It is yet another object of the present invention to reduce the usage level of ZPTO in
formulations, especially in cosmetic formulation, as well as in antifouling formulation and
paints, to reduce the chemical threat to environment, especially to aquatic environment
and emulate green chemistry.
SUMMARY OF THE INVENTION
According one aspect of the present invention there is provided a stable personal care
formulation for use on skin, scalp and hair, said formulation comprising:
0.01 to about 10% w/w Zinc Pyrithione having antifungal activity; and
0.01% to about 20% w/w Amino acid and/or its derivatives, most preferably
histidine, a water-soluble imidazole derivative, cysteine or its derivatives thereof.
According to another aspect of the present invention there is provided a stable personal
care formulation comprising:
a) 0.1 -25% w/w of a surfactant;
b) 0.01 to 10% w/w soluble zinc pyrithione; and
c) buffer salts and other ingredients, balance being water;
wherein said formulation has pH ranging from 5.5 to 8.5.
According to another aspect of the present invention there is provided a stable
transparent aqueous solution comprising:
a) 0.01 to 10% w/w Zinc Pyrithione having antifungal activity;
b) 0.01 to 20% w/w Amino acid and/or its derivatives, and/or
c) 0.01 to 20% w/w Imidazole and/or its derivatives, and/or
d) 0.01 to 20% w/w Organic compounds with thiol functionality and/or its
derivatives; and
e) buffer salts and other ingredients, balance being water;
Wherein said solution has pH ranging from 5.5 to 8.5.

According to yet another aspect of the present invention there is provided a process for
production of the stabilized transparent aqueous solution for use in personal care
compositions, said process comprising steps of:
(i) mixing of Zinc Pyrithione powder in an alkaline solution;
(ii) adding mixture prepared in step (i) to a buffer solution containing Amino acid
and or its derivatives, most preferably Pyrrolidone Carboxylic Acid-Na (PCA-
Na); histidine; a water soluble imidazole derivative; cysteine or its derivatives
to form an intermediate solution;
(iii) adjusting pH of the intermediate solution to less than pH < 8 by an acid and
(iv) finally filtering (<0.45 m) the solution of step (iii) to form the stabilized
transparent aqueous solution.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a clear aqueous solution of Zinc Pyrithione (ZPTO) of
concentration 0.01 to 10% at pH 5.5 to 8.5 preferably at pH 6.5-7.5 in aqueous medium.
The stabilized clear aqueous solution of ZPTO is prepared by dissolving ZPTO powder
in NaOH solution. The resultant solution was added to a buffer solution saturated with
amino acid or its derivatives selected from Na-PCA, Histidine, a water-soluble imidazole
derivative and cysteine or its derivatives, such that the final pH of this clear solution is 9.
To the above solution, 1.0M to 10 M HCI is added dropwise until the solution pH is less
than 8.0. The solution was filtered (Whatman 52) for removal of any suspended particles
and the clear supernatant is collected. The clear solution of ZPTO has the following
characteristics:
1. The clear suspension has pH ~7.0
2. The clear aqueous suspension is capable of inhibiting growth of fungal strain
(e.g. M. furfur, Candida albicans)
3. Around 0.06% transparent ZPTO solution was found to produce same or higher
efficacy when compared with 1 % ZPTO
4. The clear solution is stable under storage conditions.
The amount of amino acid or its derivatives present in the solution is about 0.01 to 20%
w/w preferably from 0.01 to 15% w/w. The amino acid or its derivatives is selected from

Histidine, water-soluble imidazole derivative, organic compounds with thiol functionality
like cysteine or its derivatives and mixtures thereof.
Microbiological testing has shown that the clear homogeneous solution of ZPTO showed
enhanced activity than parent ZPTO.
The advantages in using the present transparent solution are that lower dosage of ZPTO
is used which has the same efficacy in comparison to normal suspension of ZPTO in
water and which also provides mildness attribute to the system.
It is also desirable from an environment viewpoint that the amount of ZPTO that is
disposed to the environment is as low as possible due to its potential threat to aquatic
systems/animals. So the present invention in addition to making a clear, efficacious
ZPTO solution imposes a significantly lesser environmental load.
The present clear ZPTO solution can be used in liquid, gel or serum shampoos; bar,
liquid, gel, foam or serum soap; antifouling formulations; conditioners; anti-acne
formulations, anti-fungal sprays and combinations thereof. More preferably it can be
used in transparent hair care products, especially in antidandruff shampoo, antidandruff
hair gel, antidandruff hair soap and hair care serums; in skin care products especially in
soap and wipes; in anti-acne ointments; conditioner products; in transparent antifouling
formulations, especially in transparent non-staining fabric cleanser; transparent
antifungal sprays.
The present invention of soluble clear ZPTO solution can be used in a variety of hair
care products that are translucent or opaque, where the consumer desires the visual
sensory yet demands the need for the functional benefit of the soluble or insoluble
ZPTO. The use of the ZPTO solution of the present invention is not limited to personal
care products, antifungal ointments or paints but to any environment friendly products
having desired antifungal, antimicrobial or anti-inflamatory activity.
The present invention is illustrated by the following examples and figures. It is to be
understood that the disclosed methodology is not limited to the exact details briefed here
and variations to implement the idea are possible. The methodology described is for the
purpose of description and should not be taken as limitation.

Example 1
1.0g of ZPTO powder was dissolved in 10 ml of 10 % NaOH solution (1g NaOH pellet +
10 ml of water). A part of the above clear ZPTO solution was then added in an amino
acid (Na-PCA; Histidine; a water soluble imidazole derivative; cysteine or its derivatives)
buffer solution (9.5 - 12.5g w/w). The pH of this clear solution was 9. In this clear
solution, excess histidine remained as precipitate at the bottom. To the above solution,
1M to 10 M HCI was added drop wise until the solution pH reached less than 8.0 (at
7.0±0.5). The solution was filtered through Whatman 52 filter paper (<0.42l m) for
removal of any suspended particles and the clear supernatant was collected.
Example 2
The clear solutions as obtained by the process discussed in example 1 were tested for
antifungal efficacy against M. furfur.
The antifungal activity was evaluated in solid medium by measuring the zones of
inhibition, using Malassezia furfur strains. M. furfur was seeded on agar plate and 10I I
of the test solution was placed at the center of the plate, marked with 6mm (diameter)
disk. The plate was incubated at 30°C and the Zone of Inhibition was assessed from the
measurement of the ring of inhibition. The procedure was repeated at least three times
using sample from different batch for testing reproducibility.
The results obtained from the inhibition tests are provided in Table 1. It clearly shows
how the present invention is superior in terms of efficacy at a much lower concentration.
Example 3
The clear aqueous solution, as obtained by the process described in example 1, is used
as an active in a clear, transparent anti dandruff shampoo with the following formulation.
We claim :
1. A stable personal care formulation for use on skin, scalp and hair, said
formulation comprising:
0.01 to about 10% w/w Zinc Pyrithione having antifungal activity; and
0.01% to about 20% w/w Amino acid and/or its derivatives, most preferably
histidine, a water-soluble imidazole derivative, cysteine or its derivatives thereof.
2. A stable personal care formulation comprising:
a) 0.1 -25% w/w of a surfactant;
b) 0.01 to 10% w/w soluble ZPTO; and
c) buffer salts and other ingredients, balance being water;
wherein said formulation has pH ranging from 5.5 to 8.5.
3. A stable transparent aqueous solution comprising:
a) 0.01 to 10% w/w Zinc Pyrithione having antifungal activity;
b) 0.01 to 20% w/w Amino acid and/or its derivatives, and/or
c) 0.01 to 20% w/w Imidazole and/or its derivatives, and/or
d) 0.01 to 20% w/w Organic compounds with thiol functionality and/or its
derivatives; and
e) buffer salts and other ingredients, balance being water;
wherein said solution has pH ranging from 5.5 to 8.5.
4. The stable personal care formulation as claimed in claims 1 or 2, wherein the
said formulation is transparent.
5. The stable personal care formulation as claimed in claim 1 preferably comprises
0.01% to 1.5% by weight of said Zinc Pyrithione.
6. The stable personal care formulation as claimed in claim 2 preferably comprises
0.01 % to 1.5% by weight of said Zinc Pyrithione.
7. The stable personal care formulation as claimed in claims 1, wherein said amino
acids are preferably histidine or cysteine.
8. The stable personal care formulation as claimed in claim 1, wherein said
formulation preferably comprises 0.01% to 20% by weight of the said amino acid
and/or its derivatives.
9. The stable personal care formulation as claimed in claim 1, wherein said
formulation comprises more preferably 0.01% to 15% by weight of the said amino
acid and/or its derivatives.
10. The stable personal care formulation as claimed in claim 1, wherein said
formulation preferably comprises 0.01% to 15% by weight of the said imidazole
and/or its derivatives.
11. The stable personal care formulation as claimed in claim 1, wherein said
formulation preferably comprises 0.01% to 15% by weight of the said organic
compounds with thiol and/or its derivatives.
12. The stable transparent aqueous solution as claimed in claim 3, wherein said
amino acids are preferably histidine and cysteine.
13. The stable transparent aqueous solution as claimed in claim 3, wherein said
solution preferably comprises 0.1% to 20% by weight of the said amino acid
and/or its derivatives.
14. The stable transparent aqueous solution as claimed in claim 3, wherein said
solution comprises more preferably 0.1% to 15% by weight of the said amino
acid and/or its derivatives.
15. The stable transparent aqueous solution as claimed in claim 3, wherein said
solution preferably comprises 0.1% to 15% by weight of the said imidazole and/or
its derivatives.
16. The stable transparent aqueous solution as claimed in claim 3, wherein said
solution preferably comprises 0.1% to 15% by weight of the said organic
compounds with thiol and/or its derivatives.
17. The stable personal care formulation as claimed in claim 1, 2 or 4 wherein the
said formulation is selected from liquid, gel or serum shampoos; bar, liquid, gel,
foam or serum soap; antifouling formulations; conditioners; anti-acne
formulations, anti-fungal sprays and combinations thereof.
18. A process for production of the stable transparent aqueous formulation for use in
personal care compositions, said process comprising steps of:
(i) Mixing of suspension or solid powder of Zinc Pyrithione powder in an alkaline
solution of pH >10
(ii) Adding mixture prepared in step (i) to a buffer solution containing amino acid
and or its derivatives and or a water soluble imidazole derivative and or an
organic compound with thiol functional group or its derivatives to form an
intermediate solution;
(iii) Adjusting pH of the intermediate solution to less than 8.0 by an acid and
(iv) Optionally finally filtering the solution of step (iii) to form the stabilized
transparent aqueous formulation,
(v) Mixing of the solution from step (iv) to a surfactant solution in desired
proportion to obtain a formulation along with other desired ingredients.
19. A stable personal care formulation, stable transparent aqueous solution and a
process for preparation of the same as described herein with reference to
examples.

The present invention provides a clear, stabilized and transparent aqueous solution of
Zinc Pyrithione (ZPTO) at a lower concentration, which produces higher efficacy than
1 % ZPTO suspension.