Details for Patent: 5,145,675

Title:	Two step method for preparation of controlled release formulations
Abstract:	Active substances intended for topical application are incorporated in novel formulations in which they are retained as impregnants inside the pores of porous solid particles or microspheres. The pores form a continuous network open to the exterior of the particles, permitting outward diffusion of the impregnants at a controlled rate depending on the pore size. The impregnated particles are prepared by impregnation of preformed particles with the active substance.
Inventor(s):	Won; Richard (Palo Alto, CA)
Assignee:	Advanced Polymer Systems, Inc. (Redwood City, CA)
Filing Date:	Jan 23, 1991
Application Number:	07/644,869
Claims:	1. A method for preparing a delivery system for an active substance, said method comprising: polymerizing monomers suspended in an immiscible phase in the presence of a porogen to form a plurality of rigid cross-linked polymer beads each defining a substantially non-collapsible internal pore network having residual porogen therein, wherein the beads have a cross-linking density in the range from 20% to 80% and the pore network is open to the exterior of the beads; extracting substantially all residual porogen from the internal pore network; and introducing the active substance into the internal pore network after the porogen has been substantially completely extracted, whereby the porogen and polymerization conditions may be selected to provide pore dimensions which result in desired release characteristics for an active substance from the beads. 2. A method as in claim 1, further comprising removing unbound organic species from the internal pore network by washing the beads in a solvent after the residual porogen has been extracted and drying the solvent prior to introducing the active substance. 3. A method as in claim 1, further comprising topically applying the beads onto skin after the active substance has been introduced. 4. A method as in claim 1, further comprising introducing the beads into a topical carrier after the active substance has been introduced in the internal pore network. 5. A method as in claim 1, wherein the beads have a diameter in the range of from about 10 microns to about 40 microns. 6. A method as in claim 1, wherein the monomers are selected and polymerized under conditions which result in rigid cross-linked polymer beads having a total pore volume in the range from about 0.01 cc/g to about 4.0 cc/g, a surface area in the range from about 1 m.sup.2 /g to about 500 m.sup.2 /g, and an average pore diameter in the range from about 0.001 microns to about 3.0 microns. 7. A method as in claim 6, wherein the pore volume is in the range from about 0.1 cc/g to about 2.0 cc/g, the surface area is in the range from about 20 m.sup.2 /g to about 200 m.sup.2 /g, and the average pore diameter is in the range from about 0.003 microns to about 1.0 microns. 8. A method as in claim 1, wherein the monomers are selected to produce a copolymer selected from the group consisting of styrene-divinylbenzene and methyl methacrylate-ethylene glycol dimethacrylate. 9. A method as in claim 1, wherein the active substance is heat or radiation labile. 10. A method as in claim 9, wherein the active substance is selected from the group consisting of ultraviolet absorbants, vitamins, insect repellents, steroids, acne treatments, counterirritants, vitamins, and hair growth promotants. 11. A method as in claim 10, wherein the active substance is an ultraviolet absorbent selected from the group consisting of aminobenzoates, cinnamates, benzones, and salicylates. 12. A method as in claim 10, wherein the active substance is a retinoid. 13. A method as in claim 10, wherein the active substance is an insect repellent selected from the group consisting of terpenoids, benzoquinones, aromatics, and synthetics. 14. A method as in claim 10, wherein the active substance is a steroid selected from the group consisting of fluocinolone, flulocinolone acetonide, triamcinolone acetonide, betamethasone valerate, timobesone acetate, hydrocortisone, hydrocortisone acetate, triamcinolone, prednisolone, prednisolone acetate, dexamethasone, beclomethasone dipropionate, betamethasone dirporpionate, betamethasone benzoate, clocortolone pivalate, halcinonide, flumethasone, pivalate, and desonide. 15. A method as in claim 10, wherein the active substance is an acne treatment selected from the group consisting of benzoylperoxide, salicylic acid, and resorcinol. 16. A method as in claim 10, wherein the active substance is a counterirritant selected from the group consisting of camphor, methanol, and methyl salicylate. 17. A method as in claim 10, wherein the active substance is a fragrance selected from the group consisting of flower oils, essential oils from plants, animal scents, and synthetic substances. 18. A method as in claim 10, wherein the active substance is minoxidil.