Inhibition of hair growth

[0002] The invention relates to the inhibition of hair growth.

[0003] Arachidonic acid is released from membrane lipids in response to injury or other irritation. The enzyme cyclooxygenase converts arachidonic acid into cyclic endoperoxides commonly known as PGG₂and PGH₂. The endoperoxides subsequently are converted into prostoglandins, which are the primary mediators of inflammation in the body.

[0004] It has now been found that mammalian (including human) hair growth can be inhibited by applying to the skin a composition including an inhibitor of cyclooxygenase in an amount effective to reduce hair growth in the applied area.

[0005] The preferred inhibitors are commonly known as non-steroidal anti-inflammatory drugs (NSAIDs). These drugs include compounds from a variety of chemical classes.

[0006] One preferred class of NSAIDs are propionic acids, which include α-methyl-4-[2-methylpropyl]benzeneacetic acid (ibuprofen), 6-methoxy-α-methyl-2-naphthaleneacetic acid (naproxen), 2-[3-phenoxyphenyl]propionic acid (fenoprofen), 2-[3-benzoylphenyl]propionic acid (ketoprofen), gamma-oxo[1,1′-biphenyl]-4-butanoic acid (fenoprofen), and 6-chloro-α-methylcarbazole-2-acetic acid (carprofen).

[0007] Another preferred class of NSAIDs are indoleacetic acids, which include 1-[p-chlorobenzoyl]-5-methoxy-2-methylindole-3-acetic acid (indomethacin), 5-fluoro-2-methyl-1-[(4-(methylsulfinyl)phenyl) methylene]-1H-indene-3-acetic acid (sulindac), 1-methyl-5-[p-toluoyl]pyrrole-2-acetic acid (tolmetin), 2-[(2,6-dichlorophenyl)amino]benzeneacetic acid (diclofenac).

[0008] A third preferred class of NSAIDs are salicylates, which include 2-acetoxybenzoic acid (acetylsalicylic acid) and 5-[2,4-difluorophenyl]salicylic acid (diflunisal).

[0009] A fourth preferred class of NSAIDs are anthranilic acids, which include 2-[(2,6-dichloro-3-methylphenyl) amino]benzoic acid (meclofenamic acid) and 2-[(2,3-dimethylphenyl) amino]benzoic acid (mefenamic acid).

[0010] A fifth preferred class of NSAIDs are enolic acids, such as 4-hydroxy-2-methyl-N-2-pyridinyl-2H-thieno[2,3-e]-1,2-thiazine-3-carboxamide-1,1-dioxide (tenoxicam).

[0011] Other NSAIDs like 4-[6-methoxy-2-naphthyl]-2-butanone (nabumetone) also can be used.

[0012] The composition preferably includes a non-toxic dermatologically acceptable vehicle or carrier which is adapted to be spread on the skin. Examples of suitable vehicles are acetone, alcohols, or a cream, lotion, or gel which can effectively deliver the active compound. In addition, a penetration enhancer may be added to the vehicle to further enhance the effectiveness of the formulation.

[0013] The concentration of the inhibitor in the composition may be varied over a wide range up to a saturated solution, preferably from 1 to 30% by weight or even more; the reduction of hair growth increases as the amount of inhibitor applied increases per unit area of skin. The maximum amount effectively applied is limited only by the rate at which the inhibitor penetrates the skin. Generally, the effective amounts range from 100 to 3000 micrograms or more per square centimeter of skin.

[0014] The composition should be applied to the area of the body where it is desired to inhibit hair growth. Typically, the composition can be applied to the face, particularly to the beard area of the face, i.e., the cheek, neck, upper lip, and chin. The composition can also be applied to the legs, arms, torso or armpit. The composition is particularly suitable for the treatment of hirsatism. In humans, the composition should be applied once or twice a day, or even more frequently, for at least three months to achieve a perceived reduction in hair growth.

[0015] Reduction of hair growth is demonstrated when the frequency of hair removal is reduced, or the subject perceives less hair on the treated site, or quantitatively, when the weight of hair removed by shaving (i.e., hair mass) is reduced. Male intact Golden Syrian hamsters are considered acceptable models for human beard hair growth in that they display oval shaped flank organs, one on each side, each about 8 mm. in major diameter, which grow thick black and coarse hair similar to human beard hair. These organs produce hair in response to androgens in the hamster.

[0016] To evaluate the effectiveness of a particular inhibitor in reducing hair growth, the flank organs of each of a group of hamsters are depilated by applying a thioglycolate based chemical depilatory (Surgex). To one organ of each animal 10 μl. of vehicle alone once a day is applied, while to the other organ of each animal an equal amount of vehicle containing the inhibitor is applied. After thirteen applications (one application per day for five days a week), the flank organs are shaved and the amount of recovered hair (hair mass) from each is weighed. Percent-reduction of hair growth is calculated by subtracting the hair mass (mg) value of the test compound treated side from the hair mass value of the vehicle treated side; the delta value obtained is then divided by the hair mass value of the vehicle treated side, and the resultant number is multiplied by 100.

[0017] The preferred cyclooxygenase inhibitors were tested according to the above procedure. The results are presented in Table 1; the vehicles used to deliver the inhibitors are reported in Table 2.

[0018] A preferred inhibitor, indomethacin, was tested for inhibition of hair growth in various formulations. The results are presented in Table 3.

[0019] It will be appreciated by those skilled in the art that the invention can be performed within a wide range of equivalent parameters of composition and conditions without departing from the spirit or scope of the invention or of any embodiment thereof.