Improved Intestinal Absorption of an Enteric-Coated Sodium Ursodeoxycholate Formulation

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Abstract
A new enteric-coated formulation of sodium ursodeoxycholate was prepared and administered to man. The barrier film disintegrates and releases the drug only at pH ≥5.5. The sodium salt of glycoursodeoxycholate was also prepared and encapsulated like ursodeoxycholate. Serum levels of ursodeoxycholate and glycoursodeoxycholate were measured by specific enzyme immunoassay after oral administration of their sodium salts in an enteric-coated formulation at equimolar doses of 475 and 540 mg. The same subjects also received in separate experiments ursodeoxycholic acid, sodium ursodeoxycholate, and glycoursodeoxycholic acid in gelatin capsules. The mean area under the curve (µmol/L ·hr) following administration of enteric-coated sodium ursodeoxycholate (45±8) was significantly higher than that of either ursodeoxycholic acid (26 ±5 ; P < 0.01) or sodium ursodeoxycholate (25±6; P < 0.001) administered in a conventional gelatin capsule. No differences were found when glycoursodeoxycholic acid was administered as an enteric-coated sodium salt or in acid form in gelatin capsules. Ursodeoxycholic was administered at a dose of 10 µmol/min/kg over 1 hr to bile fistula rats both intraduodenally (i.d.) and intravenously (i.v.). The experiment included administration of the sodium salt in solution and the acid as a suspension. A similar experiment was performed with glycoursodeoxycholic acid. The ratio of the amount recovered from bile in the i.d. to that in the i.v. experiment is almost 1 for the sodium salt of ursodeoxycholate in solution, while it drops to 0.55 for ursodeoxycholic acid. No differences were found between i.v. and i.d. administration when glycoursodeoxycholic acid was administered in acid form and as a soluble sodium salt. The results in rats point out that the limiting factor for ursodeoxycholic acid intestinal absorption is its poor solubility and the high pH (8.4) it requires for micellar solubilization. On the other hand, glycoursodeoxycholic acid is well absorbed either in acid form or as a sodium salt because of its higher solubility at lower pH (6.4). The new enteric-coated sodium ursodeoxycholate formulation resulted in complete solubilization and increased absorption.