Method of Increasing Oral Absorption of Polar Bioactive Agents

1. Field of the Invention

The present invention relates to the oral delivery of polar bioactive agents particularly polypeptides which by this route are slowly absorbed and more especially to the enhancement of this delivery by formulations which contain a hydroxyaromatic acid.

As employed in this application, the term "polar bioactive agents" refers to those therapeutic substances which, due to their polar nature, are slowly absorbed from the gastrointestinal tract and include particularly, polypeptides which have three or more residues of amino acids with a molecular weight of 4000 or less.

2. Description of the Prior Art

It is well known to the art that a number of bioactive agents are so polar that they are only slowly absorbed from the gastrointestinal tract. Consequently, these agents, on the basis of the current art, must be administered by the intravenous or intramuscular route or in excessively large oral doses in order to attain clinical efficacy. Similarly, there are a number of other polar bioactive agents such as the polypeptides which, due to their hydrophilic nature, are also slowly absorbed from the gastrointestinal tract. The hydrophilic, polar nature of these agents precludes their rapid absorption so that even the small percentage which is absorbed is subject to a long residency time in the gastrointestinal environment where both acidic and enzymatic degradation contribute to their poor bioavailability. It is therefore clear that any factor which enhances the rate of absorption will demonstrate improved clinical efficacy.

Many attempts have been made to improve the oral absorption of these polar bioactive agents. The degradation caused by the gastric acid and enzymes can be partially overcome by coating. This process in some instances can lead to some enhanced oral absorption, but in no case does it allow complete absorption. Other approaches center on the reduction of the hydrophilicity by preparing a chemical derivative which is more lipophilic. The more lipophilic derivative is more rapidly absorbed so that the residency time in the degrading gastric medium is minimized.

In spite of the numerous attempts to prepare a dosage form of these polar bioactive agents, there still exists a clear and present need for a novel method to enhance the oral absorption of polar bioactive agents, particularly polypeptides. Said method would permit the oral use of a number of polypeptides, and would provide an improved oral dosage form for such polypeptides.

Accordingly, a major object of this invention is to provide a class of agents or adjuvants which enhance the oral absorption of polypeptides (polar bioactive agents).

Another object is to provide a process utilizing said class of agents to enhance the oral absorption of polypeptides.

Another object is to provide a stable drug form utilizing said class of agents which when administered orally will provide increased blood levels of the therapeutic agent.

Other objects, features and advantages of the invention will be apparent to those skilled in the art from the detailed description of the invention which follows.

All of the foregoing objects are readily attained by providing a method and drug form wherein the oral absorption of polar bioactive agents, particularly polypeptides, is enhanced, the method comprising the steps of preparing a drug form suitable for oral delivery, and a drug form comprising an effective unit dosage amount of the polypeptide drug agents, a hydroxyaromatic acid or salt thereof, the latter adjuvants being present in said drug form in an amount sufficient to be effective in enhancing the rate of the oral absorption of the therapeutic substance, and a suitable pharmaceutically acceptable excipient.

The present invention, generally comprises the steps of preparing a drug form capable of being orally administered, wherein the drug form comprises an effective unit dosage amount of a polypeptide drug and a hydroxyaromatic acid or salt thereof, the hydroxyaromatic acid or salt thereof being present in the drug form in a sufficient quantity to be effective in enhancing the oral absorption rate and administering the drug form to warm-blooded animals. The amount of polypeptide varies over a wide range, but generally any therapeutically effective unit dosage amount of the selected polypeptide is used.

The hydroxyaromatic acids or their salts thereof that are used as the adjuvants in our method and in our drug forms have the following structural formulae including the various isomers possible within the formulae set forth: ##STR1## wherein R.sub.1 is CO.sub.2 H, --(CH.sub.2)--COOH, ##STR2## SO.sub.3 H, or a pharmaceutically acceptable salt thereof such as the sodium salt or the calcium salt wherein R.sub.2 is OH, H, a lower alkoxy radical including methoxy, ethoxy, butoxy, or octyloxy, a lower alkyl radical including methyl, isopropyl, ethyl, t-butyl, n-butyl, or t-octyl, a halo radical, or a tri-halo lower alkyl radical including trifluoromethyl, and wherein y is an integer of 1 or 2.

More preferred adjuvants of Formula I are those compounds wherein the R.sub.1 and OH groupings are ortho to each other.

Specific adjuvants useful in our method and drug forms for enhancing oral absorption of the polypeptide agents include the following:

1. Sodium salicylate

2. Sodium-5-methoxysalicylate

3. Sodium-5-chlorosalicylate

4. Sodium-5-bromosalicylate

5. 5-trifluorosalicylic acid

6. 3-t-butyl-5-methylsalicylic acid

7. Sodium-5-t-octylsalicylate

8. Sodium-3,5-diiodosalicylate

9. 5-n-butyoxysalicylic acid or

10. 3-t-butyl-6-methylsalicylic acid

Such adjuvants are not considered novel per se and may be prepared by techniques known to those skilled in the art.

The amount of adjuvant of Formula I used in our method and drug forms may vary over a wide range; in general, the identity and the amount of the adjuvant used in connection with the drug is such to be effective in enhancing the absorption rate of the drug from the gastrointestinal compartment into the bloodstream. Generally the amount of adjuvant used per unit dosage of the particular drug being administered is in the range of 50 mg to 750 mg. The amount of adjuvant to be effective will vary depending on the particular drug used and the release characteristics of the particular dosage form used. (For example, a rapidly disintegrating drug delivery device or a slow release device will have different adjuvant requirements.) The effectiveness of the adjuvants becomes significant at local concentration exceeding 0.01% at the absorption site. Their use at a dosage whereby their concentration at the absorption site exceeds 5% is not recommended because of the local irritating effect on the tissue.

The polypeptide agents whose enhanced oral delivery is a subject of the present invention encompasses polypeptides having three (3) or more residues of amino acids and having a molecular weight of 4000 or less. Examples of polypeptides which fall within the above parameters are the following:

bradykinin

somatostatin

calcitonin

endorphin

secretin

oxytocin

T.S.H. (thyrotropin) or

Cyclo-(N-Me-Ala-Tyr-D-Trp-Lys-Val-Phe)

The quantity of these polypeptide agents necessary for preparing the drug form could vary over a wide range, but would normally be regulated by that quantity necessary to comprise the therapeutically effective dosage form.

The drug forms of this invention are suitably administered in oral dosage form, such as by tablet or capsule, by combining the polypeptide agent in a therapeutic amount and the adjuvant of Formula I in a sufficient quantity to be effective to enhance oral delivery with an oral pharmaceutically acceptable inert carrier, such as lactose, starch (pharmaceutical grade), dicalcium phosphate, calcium sulfate, Kaolin, mannitol and powdered sugar. In order to reduce the irritation in the stomach, the preferred dose form of the adjuvant of Formula I should be a pharmaceutically acceptable salt and the drug form should be designed to release the polypeptide agent and the hydroxyaromatic acid salt beyond the pylorus. In addition, when required, suitable binders, lubricants, disintegrating agents, and coloring agents can also be added. Typical binders include, without limitation, starch, gelatin, sugars such as sucrose, molasses, and lactose, natural and synthetic gums, such as acacia, sodium alginate, extract of Irish moss, carboxymethylcellulose, methylcellulose, and polyvinylpyrrolidone, polyethylene glycol, ethylcellulose and waxes. Typical lubricants for use in these dosage forms can include, without limitation, boric acid, sodium benzoate, sodium acetate, sodium chloride, leucine and polyethylene glycol. Suitable disintegrators can include, without limitation, starch, methylcellulose, agar, bentonite, cellulose and wood products, alginic acid, guar gum, citris pulp, carboxymethylcellulose, and sodium lauryl sulfate. Optionally, if desired, a conventionally, pharmaceutically acceptable dye can be incorporated into oral dosage unit form, e.g., any of the standard FD & C dyes.

Typical preparation of enteric-coated tablets containing adjuvant.

All ingredients except 1/4 of the magnesium stearate were mixed and the material slugged using 1/2" flat head punches. The slugs were broken up and passed through a 40 mesh screen. The remaining magnesium stearate was added and mixed in. Tablets were made with 7/16" deep concave punches to a hardness of 10 Kg.

Coating:

The tablets were coated with 11 mg of pre-coat and 32 mg of enteric coating according to the coating procedure described below.

Tablets or capsules were placed in a coating pan containing baffles to provide adequate tumbling. A small amount of the coating solution was applied using an air sprayer and the solvents evaporated with a warm air supply directed into the coating pan. This procedure was repeated until the desired amount of coating material was applied. The amount of coating material was determined from the weight gain of a representative group of tablets.

Coating Solutions:

Pre-coat: A film of hydroxypropylmethylcellulose was applied to the tablets followed by an enteric coating.

Enteric coat: A film of hydroxypropylmethyl- cellulosephthalate was applied.

Solutions: A 5% by weight solution of hydroxypropylmethylcellulose and a 10% by weight solution of hydroxypropylmethylcellulosephthalate in ethanol:methylene chloride (1:1 by weight) were used as the coating solutions.

The following tests were run showing Percent Bioavailability (% BA)

The above tests were done according to the following protocol:

For the oral test an intraduodenal injection 1.0 cm distal to the pylorus was done . The volume of the injection was 0.25 ml at 0.3 ionic strength (adjusted with sodium chloride) and a pH of 5.

The drug was administered at 10 mg/ml unless otherwise noted and the adjuvant at 20 mg/ml unless otherwise noted.

The (AUC)i.v. was determined for each drug, based on the mean value from 3-6 animals.

Any skilled artisan concerned with the subject matter of this invention can prepare these oral dosage forms by simply referring to the oral dosage form preparatory procedure outlined in REMINGTON'S PHARMACEUTICAL SCIENCES, Fifteenth Edition (1975), pages 1576 through 1617 inclusive.

From the foregoing description, one of ordinary skill in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to varius usages and conditions. As such, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.