ORAL DRUG DELIVERY SYSTEM FOR ENHANCING THE BIOAVAILABILITY OF ACTIVATED GLYCYRRHETIN

Abstract: A drug delivery system for enhancing the bioavailability of glycyrrhizin is disclosed. The system is a colon-targeted, oral drug delivery system containing a sufficient amount of glycyrrhizin to overwhelm the rate of hydrolysis thereof by the intestinal flora in admixture with a pharmaceutically acceptable carrier. Preferably all or a part of the carrier consists of an adsorption promoter selected from the group consisting of a pharmaceutically acceptable organic acid, a surfactant and a chelating agent.

Description: The present invention relates to a drug delivery system for oral administration of glycyrrhizin. More particularly, it relates to such a drug delivery system for enhancing the bioavailability of glycyrrhizin. Glycyrrhizin is a naturally occurring substance found in licorice root ( Glycyrrhiza glabra L .) that has long been used as a Chinese medicine. It has a strong sweet taste and is used as a sweetener. In addition, glycyrrhizin is used in the treatment of chronic hepatitis, allergic disorder and other pathological conditions by its intravenous administration. Chemically glycyrrhizin is a glucuronide of glycyrrhetic acid with two moles of glucuronic acid. Several studies on the pharmacokinetic behavior of glycyrrhizin in human and animals have revealed that glycyrrhizin is scarcely detectable in the blood following oral administration but its hydrolyzed product, glycyrrhetic acid, is detectable in the blood. See, Wang, Z. et al., Biol. Pharm. Bull. 17(10):1390-1403(1994); Yamamura, Y. et al., ibid., 18(2):337-341(1995); and Takeda, S. et al., J. Pharm. Pharmacol. 48:902-905(1996). Accordingly, it has been considered that glycyrrhizin is poorly absorbable from digestive tract as such (active form), and hydrolyzed in the digestive tract into glycyrrhetic acid which is known to have only little therapeutic effect on hepatitis. Since glycyrrhizin is mainly absorbed in this form, its bioavailability is very low. In order to enhance the bioavailability, rectal administration of glycyrrhizin in the form of a rectal suppository was proposes (JP-A-01294619, JP-A-03002122 JP-A-03123731 and JP-A-04261117). Other attempts to enhance absorbability from digestive tract include providing an enteric oral preparation containing a fatty acid glyceride (JP-A-03255037) and an oral preparation containing a lipid emulsion or lipid complex (JP-A-06192107). With these prior art suppository and oral preparations, however, the blood concentration of glycyrrhizin does not reach a level sufficient to exhibit its therapeutic effect. EP-A 535 704 discloses a glycyrrhizin suppository comprising glycyrrhic acid or salts thereof and a non-ionic surface active agent in addition to an oleaginous base for suppositories. US-A 5,637,319 describes oral controlled-release preparations suitable to deliver drugs to different sites of gastro-intestinal tract and suitable to control the release rate of drugs. One embodiment is an oral intestinal pressure-controlled release preparation. When the preparation, such as an ethylcellulose made capsule, is disintegrated by the inner pressure of the large intestine, drug solution or drug suspension contained in the capsule is released. There exists a need for a method and device for enhancing the bioavailability of active glycyrrhizin in oral route to a therapeutically effective level. According to the present invention, the above need is met by providing a device for colon-targeted oral delivery of glycyrrhizin comprising a shaped core containing an amount of glycyrrhizin, said shaped core being made of a suppository base that comprises higher fatty acid di- and triglycerides and melts or liquefies at the body temperature, and a coating film of ethylcellulose enclosing said shaped core and having a film thickness whereby when the device is transported through the digestive tract to the colon, the film enclosing the liquefied core ruptures selectively in the colon by the internal pressure generated by the peristalsis of the intestine. When glycyrrhizin is formulated into such drug delivery systems (DDS), it is released selectively in the colon at such a high concentration that saturates and overwhelms the rate of hydrolysis by the intestinal flora and, therefore, the majority of glycyrrhizin may be absorbed in the active form from the colon to achieve remarkably improved bioavailability. The drug delivery system according to the present invention basically comprises a core portion containing glycyrrhizin in admixture with a pharmaceutically acceptable carrier and a skin or shell portion enclosing the core portion. Glycyrrhizin is released and absorbed selectively in the colon upon rupture of the skin or shell portion in the colon . Preferably, the core portion contains glycyrrhizin in an amount sufficient to compensate for and substantially overwhelm the rate of hydrolysis of glycyrrhizin by the intestinal flora. The term "glycyrrhizin" as used herein includes free glycyrrhizin and a salt thereof such as sodium, potassium or ammonium salt. Preferably all or a portion of the carrier consists of a substance that promotes the absorption of glycyrrhizin. Examples of such absorption promoters include a pharmaceutically acceptable organic acid such as citric, malic, maleic, fumaric or tartaric acid; a surfactant such as sodium lauryl sulfate, polyoxyethylene sorbitan, polyoxyethylene hydrogenated castor oil, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, deoxycholate or ursodeoxycholate; or a chelating agent such as EDTA. The core portion may be produced by a method similar to those methods well known in the art for preparing oral solid preparations. It has been known in the art that the transit time of unit dosage forms for oral administration through the small intestine after expulsion from the stomach and before arrival at the large intestine (small intestine-transit time) is at around 3-4 hours whereas the time required for expulsion of such dosage forms from the stomach after administration may vary to a large extent. It is also known that a distinct rise in pH in the digestive tracts from around 1-3 in the stomach to around 6-7 in the small intestine. The colon-targeting DDS according to the present invention may be designed on the basis of these known physiological phenomenon. Now the colon-targeting DDS of the present invention will be described in detail. Since glycyrrhizin must be released in the large intestine at higher concentrations as noted above, unit dosage forms similar to rectal suppositories are well suited as a capsule content for this purpose. The method for preparing such unit dosage forms is well known in the art and comprises the steps of adding glycyrrhizin to a suitable suppository base such as Witepsol™ H15 (higher fatty acid di- and triglycerides available from Dynamit Nobel) while being in molten state to make a suspension, casting the suspension into a mold and then cooling the mold to solidify the suspension. The resulting suppository-like dosage forms are encapsulated by forming a coating film on the surfaces thereof, preferably by the dipping method. The DDS of the invention are pressure-collapsible, colon-targeted delivery capsules. This system is also disclosed in U.S. Patent No. 5,637,319 to Takada and Seizai-to-Kikai (Pharmaceutical preparations and machines), January 15, 1998 issue. This capsule is collapsed in the colon as follows. Ingested diet is flowable in the stomach and small intestine because of abundant presence of water-containing digestive juice whereas the content in the large intestine becomes highly viscous since reabsorption of water and formation of stool take place there. In such a dense environment, the capsule will rupture by the internal pressure associated with the peristalsis of colon to release the drug contained therein. The capsule is made of ethylcellulose or gelatin lined with ethylcellulose inside. Since the capsule content must be a liquid form when the capsule is collapsed, glycyrrhizin is contained in the capsule as a solution or dispersion in a base for making rectal suppositories which liquify at the body temperature. The rupture time in the colon may be controlled by varying the wall thickness of the ethylcellulose capsule. Indications of the glycylrrhizin preparation of the present invention include hepatic dysfunction in chronic hepatic disease, various eczema, drug rush, stomatitis, infant strophulus, phlyctena, alopecia areata and the like. The dose of the glycyrrhizin preparation of the present invention may be determined depending on the age, body weight, the type and severity of disease of a particular patient. The daily dose for adult patients (60kg of body weight) with chronic hepatic disease ranges between 10mg and 1,000mg, preferably between 100mg and 800mg as glycyrrhizin. This dose may be administered at once or divided twice or more. EXAMPLE The invention will be described in detail by making reference to the following non-limiting examples. Example 1 100mg of glycyrrhizin potassium salt was dispersed in 400mg of molten Witepsol™ H15 (higher fatty acid di- and triglyceride) heated at 50°C. The dispersion was poured into a mold and then cooled well to 6°C to obtain a solid article having supository-like shape. This shaped article was dusted with fine talcum powder and then coated with ethylcellulose film by the dipping method to thereby obtain a intra-colon pressure collapsible, colon-targeted delivery capsule. In vivo bioavailability test Method: The test preparation was orally administered with 50ml of water to adult beagle dogs having been fasted overnight for 12 hours. After administration, 2ml of blood samples were collected periodically over 24 hours from the jugular vein and assayed for plasma glycyrrhizin levels using HPLC. Commercial glycylrrhizin tablets (Glycyron™) were used as a control drug. The dose was 100mg as glycyrrhizin. Results: As shown in the above table, glycyrrhizin was not detected in the plasma after oral administration of commercial glycyrrhizin tables. In contrast, when the colon-targeted DDS capsule of Example 1 was orally administered, the plasma glycyrrhizin level began to rise 3 hours after the administration, reached a peak in 4-5 hours and remained at a therapeutically effective level at least up to 24 hours after the administration.

Claims: A device for colon-targeted oral delivery of glycyrrhizin comprising a shaped core containing an amount of glycyrrhizin, said shaped core being made of a suppository base that comprises higher fatty acid di- and triglycerides and melts or liquefies at the body temperature, and a coating film of ethylcellulose enclosing said shaped core and having a film thickness whereby when the device is transported through the digestive tract to the colon, the film enclosing the liquefied core ruptures selectively in the colon by the internal pressure generated by the peristalsis of the intestine. The device according to claim 1, wherein said amount of glycyrrhizin is in excess of the amount needed for compensating for the hydrolysis thereof by the intestinal flora. The device according to claim 1, obtainable by dipping the shaped core in a solution of ethylcellulose. The device according to claim 3, obtainable by dusting the shaped core with a powder to prevent from sticking before dipping. The device according to claim 1, wherein said shaped core further contains an absorption promoter for glycyrrhizin. The device according to claim 4, wherein the powder is talc. The device according to claim 5, wherein absorption promoter is an organic acid, a surfactant, a chelating agent, or a mixture thereof. A process for preparing a colon-targeted oral delivery system of glycyrrhizin comprising: (a) adding glycyrrhizin to a suppository base that comprises higher fatty acid di- and triglyderide and melts or liquefies at the body temperature while the suppository base is in molten or liquefied state to obtain a suspension; (b) casting the suspension in a mold; (c) cooling the mold to obtain a shaped solidified core of the suspension; (d) enclosing the resultant shaped core with a coating film of ethylcellulose, the coating film having a film thickness whereby when the system is transported through the digestive tract to the colon, the film enclosing the liquefied core ruptures selectively in the colon by the internal pressure generated by the peristalsis of the intestine. The process according to claim 8, wherein the amount of glycyrrhizin in said suspension is in excess of the amount needed for compensating for the hydrolysis of glycyrrhizin by the intestinal flora. The process according to claim 8, wherein said coating film is formed by dipping the shaped core in a solution of ethylcellulose. The process according to claim 8, wherein said suspension further contains an absorption promoter for glycyrrhizin. The process according to claim 8, further comprising dusting the shaped core with powder before (d) to prevent sticking of the shaped core together. The process according to claim 12, wherein the powder is talc.

Inventors: TAKADA KANJI, TAKADA, KANJI
Applicants: AMATO PHARM PROD LTD, AMATO PHARMACEUTICAL PRODUCTS, LTD.
Application year: 1999
Main classification: A61K31
IPC codes: A61K9