Drug delivery system

1. A drug delivery system comprising an intercalate of a layered double hydroxide having, before intercalation, layers of metal hydroxides, and having intercalated therein a pharmaceutically-active compound having at least one anionic group, wherein said intercalate is present in an oral dosage formulation, and which additionally comprises a non-toxic compound having an anion which is capable of displacing the pharmaceutically-active compound from the intercalate, wherein the non-toxic compound is selected from magnesium carbonate, magnesium hydrogen carbonate, calcium carbonate and calcium hydrogen carbonate.

2. The system according to claim 1 , wherein the layered double hydroxide, before intercalation, is represented by the general formula

[M II (1-x) M III x (OH) 2 ] x+ [A n− .x/n ]

in which M II is a divalent metal cation;

M III a trivalent metal cation;

A is a displaceable anion;

n is an integer; and

x is a positive number less than 1, which compound is optionally hydrated with a stoichiometric amount or a non-stoichiometric amount of water.

3. The system according to claim 2 , wherein M II is Mg or Ca and M III is Al.

4. The system according to claim 2 , wherein A is selected from OH, F, CI, Br, I, SO 4 , and NO 3 .

5. The system according to claim 2 , wherein the layered double hydroxide, before intercalation, is represented by the general formula

[M I M III 2 (OH) 6 ] + [A n− 1/n ]

in which M I is a monovalent metal cation;

M III a trivalent metal cation;

A is a displaceable anion; and

n is an integer, which compound is optionally hydrated with a stoichiometric or non-stoichiometric amount of water.

6. The system according to claim 5 , wherein M I is Li and M III is Al.

7. The system according to claim 5 , wherein A is selected from OH, F, Cl, Br, I, SO 4 , and NO 3 .

8. The system according to claim 7 , wherein the layered double hydroxide is [LiAl 2 (OH) 6 ]Cl.H 2 O.

9. The system according to claim 1 , wherein the pharmaceutically-active compound having at least one anionic group is a pharmaceutically-active compound containing at least one carboxylic acid group or a non-toxic salt thereof.

10. The system according to claim 1 , wherein the pharmaceutically-active compound is selected from 4-biphenylacetic acid, Diclofenac, Gemfibrozil, Ibuprofen, Naproxen, 2-propylpentanoic acid and Tolfenamic acid.

11. The system according to claim 1 , wherein the intercalate of a layered double hydroxide having, intercalated therein, a pharmaceutically-active compound having at least one anionic group is made by a method which comprises:

treating an aqueous solution of the pharmaceutically-active compound, optionally in the form of a non-toxic salt thereof, with the layered double hydroxide;

separating the intercalate of the layered double hydroxide.

12. The system according to claim 1 , further comprising a buffer.

13. The system according to claim 12 , wherein the buffer is a phosphate buffer.

14. A drug delivery system comprising:

an intercalate of a layered double hydroxide having, before intercalation, layers of metal hydroxides, and having intercalated therein a pharmaceutically-active compound having at least one anionic group, wherein said intercalate is in the form of particles present in an oral dosage formulation; and

a non-toxic compound having an anion which is capable of displacing the pharmaceutically-active compound from the intercalate, wherein the non-toxic compound is selected from magnesium carbonate, magnesium hydrogen carbonate, calcium carbonate and calcium hydrogen carbonate.