Title:  Alginate and gellan gum as tablet coating

United States Patent:  6,326,028

Assignee:  Monsanto Company (St. Louis, MO)

Filed:  October 30, 1998

This invention relates to coatings employed to coat medicinal tablets. Such tablets include but are not limited to small pellet(s) of medication to be taken orally. In particular this invention relates to the use of alginates and/or gellan gum, mixtures thereof and the like as tablet coatings. More in particular, this invention relates to the use of alginate and gellan gum as tablet coatings for tablets which are useful for humans including coating(s) on medicinal tablets and to a process for making such coatings.

DETAILED DESCRIPTION OF THE INVENTION

Compositions which are useful as adherent coatings herein on tablets of any kind include those which contain alginates and/or gellan gum, mixtures thereof and the like.

Tablets useful herein come in all shapes and sizes. The tablet shape and size are not critical although preferred shapes and sizes are those which can be effectively consumed by a human or animal recipient with relative ease. Preferred tablets are medicinal tablets for humans or animals.

Gellan gum is useful herein and typical useful gellan gums are those naturally occurring polysaccharides that are typically produced by inoculating a carefully formulated fermentation medium with the microorganism Sphingamonas elodea (ATTC 31461). Gellan Gum is available in a clarified form (KELCOGEL7) for foods and industrial products and a clarified form of (GELRITE7) for microbiological media, plant tissue culture, and pharmaceutical applications. Gellan gum includes non-clarified, clarified, and partially-clarified native, deacetylated and partially deacetylated forms as well as mixtures thereof and the like.

Various alginates are useful in this invention include but are not limited to those which are described in detail by I. W. Cottrell and P. Kovacs in Alginates @ as Chapter 2 of Davidson, ea., Handbook of Water-Soluble Gums and Resins (1980) which is incorporated herein by reference in its entirety.

A particularly preferred alginate useful herein is a sodium alginate, a high-G, ultra low viscosity which is available from Monsanto Company, 800 North Lindbergh Blvd, St. Louis, Mo., 63167.

Other components of the coating composition of this invention include but are not limited to a plasticizer system and color additives as will be readily apparent to those of skill in the art. A typical plasticizer is glycerine although any equivalent or substantially equivalent plasticizer may be satisfactorily employed herein.

A typical composition of this invention comprises in the range from about 0.1% to about 3% alginate and gellan gum based on the dry weight of the tablet and preferably from about 0.5% to about 1% by weight alginate and gellan gum. When employed in such a combination, the weight ratio of alginate to gellan gum is in the range from about 1 to about 20 and preferably from about 1 to about 5 although greater and lesser ratios may be employed if desired as will be apparent to those of skill in the art after reading this specification.

Alginate and gellan gum may be individually employed as a tablet coating composition in this invention.

In practicing this invention, an aqueous composition comprising alginate and/or gellan gum is admixed in any suitable vessel prior to spraying the composition onto a tablet. Preferably, but not required, the alginate and/or gellan gum is admixed with water, the plasticizer is added thereto, and further mixing is carried out to form an aqueous tablet coating composition. The composition is mixed by any suitable mixing system preferably until complete or substantial mixing has been accomplished. A hot solution may be needed. Those of skill in the art will recognize that some heating will be necessary to achieve this.

As employed herein, the term "adherent" means that the coating adheres to the tablet until consumption whereupon the coating dissolves from the tablet containing a drug in order to enable release of the active ingredient therefrom. For example, the coating is wetted in the human's mouth, the recipient swallows the wetted coated tablet and the tablet coating dissolves in the human's stomach whereupon the tablet composition is made available to the patient or recipient to receive the medicinal value of the drug.

The aforementioned admixing is carried out by any convenient means including but not limited to use of a propeller or stirrer system although generally stirring by a convenient mechanical means is acceptable.

Application of the composition as a coating to the tablet is carried out by placing the tablets to receive a tablet composition of this invention in a spray tower such as fluid bed spray tower and then spraying the composition of this invention onto the tablets.

A typical spray tower includes but is not limited to a Wurster spray tower. Also, acceptable for use to prepare coating tablets of this invention are side vented coating pans and convention coating pans with spray nozzles. Also acceptable as a spray tower system is a conventional fluid bed tower with a suitable spray apparatus is included. Any spray system capable of applying a composition of this invention to a tablet is an acceptable system for coating tablets employing the aqueous coating composition of this invention. Any size spray system is acceptable. Batch and continuous processes, semi-continuous and variations thereof are envisioned without limitation.

Although the composition of this invention will initially be an aqueous composition, the tablet coating will become dry or substantially dry upon its exit from the spray system and on the surface of the coated tablet. In practice, coated tablets prepared herein are substantially dry or dry to the human touch. The coated tablets may be placed in suitable packaging.

The tablets include but are not limited to tablets of any convenient composition which may or not contain any pharmaceutically effective drug suitable for human and/or animal consumption. This coating may be employed on those tablets which do not contain any drug for use as placebos or blanks.

The amount of biologically active in any tablet will be a function of the ability of the composition of the tablet to load the active. This will vary depending on the choice of the biologically active ingredient and the components of the tablet as those of skill in the art will recognize.

The amount of coating provided to the surface of the tablet is an effective amount and it typically that amount which provides a minimum coverage of the exterior surface area of the tablet, although this invention also encompasses those instances where there is partial coverage of the exterior surface as well.

If desired one or more layers of coating may be employed using this invention. Those of skill in the art will be able to determine such depending on the drug, tablet size, physical and chemical and therapeutic properties and characteristics from a reading of this specification and using their skill in the art. The coating or coatings of this invention may be the initial exterior surface coating, an intermediate coating, a final coating or a combination. It is preferred that the layer of coating be continuous or nearly continuous and over the surface of the tablet. An effective depth of coating is provided. It is also desired that the tablet coatings herein be somewhat resilient with handling, resistant to peeling, flaking and being rubbed off the tablet.

Claim 1 of 6 Claims

What is claimed is:

1. A coated tablet comprising a tablet and at least one coating comprising alginate and gellan gum.

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