Abstract:
There is disclosed a pharmaceutical composition of stabilized [Leu 13  ]-motilin-Hse. The composition comprises at least one of organic acids and salts thereof, as a first stabilizer, and pH thereof is adjusted in a range of 5.5-8.0. The composition may contain at least one of substances selected from saccharides, amino acids, proteins and salts thereof, as a second stabilizer. Conversion of [Leu 13  ]-motilin-Hse into [Leu 13  ]-motilin-Hse-lactone is suppressed by increasing pH value and deamidization in asparagine residue at 19-position is suppressed by the presence of the organic acid or salt thereof.

Description:
This is a continuation of application Ser. No. 07/863,251 filed Apr. 3, 1992 pending. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pharmaceutical composition of stabilized [Leu 13  ]-motilin-Hse. 
     2. Related Arts 
     Recent developments in chemical synthesis and biological application technologies make possible production of various proteins, peptides and others with desired biological activities. 
     A compound of [Leu 13  -motilin-Hse has been developed by the present inventors as the substance showing biological activities similar to native motilin (this is one of peptide hormones and shows various biological activities, and more particularly an accelerating function of digestive canal) and having possibility of large scale production with use of biotechnology, through various studies and investigations on motilin and various motilin analogues [Jap. Pat. Nos. Hei 3-80096(A) and 3-218395(A)]. Structural differences of [Leu 13  ]-motilin-Hse from native type motilin lie in that methionine (Met) residue at 13-position of an amino acid sequence coded by the native type motilin is substituted with leucine (Leu) residue, and that homoserine (Hse) residue is added at C-terminal (23-position). When biotechnologies are applied for, the [Leu 13  ]-motilin-Hse can easily be prepared with a cost less than that for preparing the native type motilin and [Leu 13  ]-motilin and shows higher biological activities than the latters [said Jap. Pat. No. Hei 3-218395(A). 
     Similar to general biologically active peptides, the motilins are apt to be affected by various external factors such as heat, humidity, light beam, and peptidases and thus stored in a refrigerator. As measures for stabilizing the motilins, then, it has been proposed to prepare an aqueous solution containing the motilin and adjusted in pH of 4.0-5.5 or lyophilize the solution [Jap. Pat. No. Hei 3-41032(A)], and to prepare a solution containing the motilin and a stabilizer selected from amino acids and proteins, or lyophilize the solution [Jap. Pat. No. Hei 3-41033(A)]. 
     In the Claims for said Jap. Pat. Nos. Hei 3-41032(A) and 41033(A), there is referred to &#34;motilins&#34; but actually stabilized motilins are native type motilin and [Leu 13  ]-motilin, only. 
     While, the motilin analogue of [Leu 13  ]-motilin-Hse has homoserine (Hse) residue at C-terminal (23-position) and thus it can not give a sufficient stability, even if pH shall be adjusted to 4.0-5.5, since there is such a possibility that the homoserine residue at 23-position shall change into lactone form in a pH range less than 5.5, even if the motilin analogue is kept in a state of aqueous solution or lyophilized powder. 
     The inventors have further found through studies and investigations on [Leu 13  ]-motilin-Hse that there is a possibility of deamidization or formation of cyclic imide in asparagine (Asp) residue at 19-position and it becomes a cause to reduce the stability of the motilin analogue, in question. 
     In other words, it is impossible to give a sufficient stabilization to the motilin analogue of [Leu 13  ]-motilin-Hse with pH adjustment only, in different from the native type motilin and [Leu 13  ]-motilin as teached in said Jap. Pat. No. Hei 3-41032(A). 
     It is preferable, further, that [Leu 13  ]-motilin-Hse shows its stability in neutral pH or pH range near thereto to reduce a stipulation, when it is administered through an injection. 
     SUMMARY OF THE INVENTION 
     A principal object of the invention is to provide a pharmaceutical composition of [Leu 13  ]-motilin-Hse by stabilizing the motilin analogue, so that the composition can be transported in ordinal conditions which require no reservation in a refrigerator. 
     The inventors have further energetically studied and investigated for developing the pharmaceutical composition of stabilized [Leu 13  ]-motilin-Hse and suitable for actual use to finally find out, surprisingly, that coexistence of an organic acid or salt thereof effectively exhibits the reaction of deamidization and formation of cyclic imide in asparagine residue at 19-position for [Leu 13  ]-motilin-Hse to establish the invention by combining this finding with the fact as referred to before, namely the finding that the homoserine residue at C-terminal shall change into lactone form in the pH range of 5.5 or more less. 
     According to the invention, therefore, the problems in the prior arts can be dissolved to attain the object by a pharmaceutical composition of stabilized [Leu 13  ]-motilin-Hse, which comprises an effective amount of [Leu 13  ]-motilin-Hse and at least one of substances of first stabilizer selected from the group consisting of organic acids and a salt thereof, and is adjusted in pH of 5.5-8.0. 
     The ground that the first stabilizer is defined as &#34;at least one of substances selected from the group consisting of organic acids and a salt thereof&#34; lies in that coexistence of an inorganic acid or salt thereof reduces a stability of [Leu 13  ]-motilin-Hse. 
     It has been found that further coexistence of at least one of substances selected from the group consisting of saccharides, amino acids and proteins to be conventionally used, mainly as a filer and additionally as a stabilizer for preparing a medicine comprising a biologically active peptide or protein serves to further stabilization of [Leu 13  ]-motilin-Hse. Therefore, the pharmaceutical composition according to the invention may contain such a substance, as a second stabilizer. 
     The [Leu 13  ]-motilin-Hse prepared by any process can be employed as the main ingredient for the pharmaceutical composition according to the invention, and without distinction of molecular type one, or a salt with an organic or inorganic acid. 
     As a pH adjusting reagent for preparing the pharmaceutical composition, any of them allowed for preparing medicines can be used, and followings may be listed; hydrochloric acid-sodium hydroxide, acetic acid-sodium acetate, glycine-sodium chloride-hydrochloric acid, potassium dihydrogenphosphate-disodium hydrogenphosphate, potassium hydrogenphthalate-sodium hydroxide, sodium secondary citrate-hydrochloric acid, sodium dihydrogenphosphate-disodium hydrogenphosphate, sodium dihydrogenphosphate-dipotassium hydrogenphosphate, potassium dihydrogenphosphate-dipotassium hydrogenphosphate, tartaric acid-sodium tartarate, lactic acid-sodium lactate, sodium barbital-sodium acetate-hydrochloric acid, succinic acid-boric acid, potassium primary citrate-sodium hydroxide, sodium primary citrate-borax, disodium hydrogenphosphate-citric acid, sodium acetate-hydrochloric acid, glutamic acid-sodium hydroxide, and aspartic acid-sodium hydroxide. Among them, hydrochloric acid-sodium hydroxide, acetic acid-sodium acetate, glycine-sodium chloride-hydrochloric acid, tartaric acid-sodium tartarate, lactic acid-sodium lactate, sodium acetate-hydrochloric acid, glutamic acid-sodium hydroxide, and aspartic acid-sodium hydroxide are preferable. 
     There is no specific limitation on the organic acid and salt thereof, which is used as the first stabilizer for preparing the pharmaceutical composition, if it shall be allowed from the view point of pharmaceutical preparation, and followings can be listed; formic acid, acetic acid, propionic acid, butyric acid, tartaric acid, valeic acid, caproic acid, caprylic acid, capric acid, lactic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumalic acid, aspartic acid, glutamic acid, citric acid, as well as a salt thereof with an alkali metal. It is preferable, in general, to use the first stabilizer in an amount of 0.01-10000 parts by weight based on 1 part of [Leu 13  ]-motilin-Hse. 
     Use of an inorganic acid or salt thereof should be avoided, since it causes reduction of the stability of [Leu 13  ]-motilin-Hse. When an aqueous solution of [Leu 13  ]-motilin-Hse, wherein 200 mM potassium dihydrogenphosphate exists, and adjusted its pH in a range of 5.5-8.0 shall be stored at 60° C. for 30 days, for instance, a remaining amount of [Leu 13  ]-motilin-Hse becomes 58.9, 35.2, 21.7 or 5.3% in pH condition of 5.5, 6.5, 7.0 or 8.0, respectively. 
     As the saccharide among the second stabilizer which is eventually used for the preparation of the pharmaceutical composition according to the invention, any of them including monosaccharides, oligosaccharides, polysaccharides, or a derivative thereof, if it shall be allowed from view point as pharmaceutical preparations, and followings may be listed; glucose, sucrose, maltose, lactose, sugar alcohol (glycerin, inositol, mannitol, megrumine or the like), hyaluronic acid, a salt thereof, heparin, inulin, chitin and a salt thereof, dextran, dextrin (molecular weight: 3000-150000), as well as a derivative of polysaccharide and salt thereof [hydroxypropylcellulose (HPC), hydroxypropylmethylcellulose (HPMC), hydroxymethylcellulose (HMC), carboxymethylcellulose (CMC), and a salt thereof]. It is preferable, in general, to use the saccharide in an amount of 0.01-10000 parts by weight based on 1 part of [Leu 13  ]-motilin-Hse. 
     There is also no limitation on the amino acid among the second stabilizer, if it shall be allowed from view point as pharmaceutical preparations, and followings may be listed; alanine, leucine, isoleucine, proline, phenylalanine, tryptophan, serine, threonine, cysteine, asparagine, glutamine, lysine, arginine, and a salt thereof. It is preferable, in general, to use the amino acid in an amount of 0.01-10000 parts by weight based on 1 part of [Leu 13  ]-motilin-Hse. 
     There is also no limitation on the protein among the second stabilizer, if it shall be allowed from view point as pharmaceutical preparations, and followings may be listed; serum albumin, serum globurin, collagen, gelatin, gelatin treated with acid (molecular weight: 7000-100000), and gelatin treated with alkali. It is preferable, in general, to use the protein in an amount of 0.01-10000 parts by weight based on 1 part of [Leu 13  ]-motilin-Hse. 
     The pharmaceutical composition according to the invention can be diluted with a pharmaceutically acceptable filer. A powder prepared by dissolving [Leu 13  ]-motilin-Hse into a refined water under coexistence of 75 mM sodium aspartate or 75 mM tartaric acid 150 mM arginine, as well as 75 mM mannitol or 75 mM lactose, adjusting pH of the solution to 6.0 or 7.0, and lyophilizing the solution was stored at 60° C. for 30 days to measure a remaining amount of the motilin analogue to find that the amount is not different from that another powder just after the lyophilization and prepared without use the saccharides as the filer. 
     A form of medicine prepared with pharmaceutical composition according to the invention may be of a solid such as tablet, pill, capsule, powder or granule for oral dosage, suppository, or liquid of solution, suspension or emulsion for injectional or oral dosage. For preparing the medicine, one or more pharmaceutically acceptable substances selected from the followings can, of course, be used in response to a selected form of medicine; reserving agent, stabilizer, antioxidant, filer, binder, disintegrator, humectant, lubricant, coloring agent, flavour, taste modifier, emulsifier, isotonizing agent, agent for inhibiting pain and the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a graph showing a relation between a remaining amount of [Leu 13  ]-motilin and pH of its solution, when aqueous solutions of the motilin analogue different in pH value were prepared, and the remaining amount was measured after stored each solution at 60° C. for 30 days; 
     FIG. 2 is a graph showing a relation of a remaining amount of [Leu 13  ]-motilin-Hse, amount of formed [leu 13  ]-motilin-Hselactone and pH of its solution, when aqueous solutions of the motilin analogue different in pH value were prepared, and the the amounts were measured after stored each solution at 60° C. for 30 days; 
     FIG. 3 is a graph similar to FIG. 2, but on a solution wherein tartaric acid was added; 
     FIG. 4 is a graph similar to FIG. 2, but on a solution wherein potassium dihydrogenphosphate was added; 
     FIG. 5 is a graph similar to FIG. 1, but on lyophilized powder which was prepared by freeze-drying the aqueous solution of [Leu 13  ]-motilin; 
     FIG. 6 is a graph similar to FIG. 2, but on lyophilized powder which was prepared by freeze-drying the aqueous solution of [Leu 13  ]-motilin-Hse. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will now be further explained in more detail with reference to Comparative Examples and Examples. 
     Comparative Example 1 
     An aqueous solution containing 20 μg/ml of [Leu 13  ]-motilin-Hse was aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin-Hse in a refined water and adding 0.1N-sodium hydroxide and 0.1N-hydrochloric acid to adjust pH of the solution to 6.0 or 7.0. 
     Each of the solutions different in pH value was aseptically charged in a glass vial to seal the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin-Hse was measured with HPLC method. 
     Results are shown in Table 1 given later. 
     Comparative Example 2 
     An aqueous solution containing 20 μg of [Leu 13  ]-motilin-Hse and 34.8 mg/ml of arginine was aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin-Hse and arginine in a refined water and adding 0.1N-sodium hydroxide and 0.1N-hydrochloric acid to adjust pH of the solution to 6.0 or 7.0. 
     Each of the solutions different in pH value was aseptically charged in a glass vial to seal the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin-Hse was measured with HPLC method. 
     Results are shown in Table 1 given later. 
     Example 1 
     An aqueous solution containing 20 μg of [Leu 13  ]-motilin-Hse and 30 mg/ml of tartaric acid was aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin-Hse and tartaric acid in a refined water and adding 0.1N-sodium hydroxide and 0.1N-hydrochloric acid to adjust pH of the solution to 6.0 or 7.0. 
     Each of the solutions different in pH value was aseptically charged in a glass vial to seal the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin-Hse was measured with HPLC method. 
     Results are shown in following Table 1. 
     
                       TABLE 1______________________________________            Remaining amount (%)*   Additive   pH 6.0    pH 7.0______________________________________Comparative     --           73.5      33.0Example 1Comparative     Arginine     64.7      40.9Example 2Example 1 Tartaric acid                  73.5      71.0______________________________________ In Table 1, *Remaining amount of [Leu.sup.13 ]-motilinHse. 
    
     It is apparent from the results shown in Table 1 that the motilin analogue causes a partial decomposition or modification in aqueous solution with higher pH value, and this phenomenon can not be sufficiently suppressed with coexistence of the amino acid but remarkably suppressed by coexistence of the organic acid. 
     Comparative Example 3 
     Aqueous solutions, each containing 20 μg/ml of [Leu 13  ]-motilin were aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin in a refined water and adding 0.1N-sodium hydroxide and 0.1N-hydrochloric acid to adjust pH of each solution in various values. 
     Each of the solutions different in pH value was aseptically charged in a glass vial to seal the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin was measured with HPLC method to check the relation with the pH value of the solution. 
     Results are shown in following Table 2 and FIG. 1. 
     
                       TABLE 2______________________________________pH value Remaining amount of [Leu.sup.13 ]-motilin (%)______________________________________3.0      22.64.0      62.84.5      64.15.0      62.35.5      60.76.0      37.86.5      25.67.0      13.48.0      9.19.0      8.0______________________________________ 
    
     It is apparent from the results shown in Table 2 that the motilin analogue ([Leu 13  ]-motilin) shows a relatively high stability by setting the pH value in a range of about 4.0-5.5 and this supports the disclosure given in Jap. Pat. No. Hei 3-41032(A) introduced in the preamble part of this specification. 
     Comparative Example 4 
     Aqueous solutions, each containing 20 μg/ml of [Leu 13  ]-motilin-Hse were aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin-Hse in a refined water and adding 0.1 N-sodium hydroxide and 0.1 N-hydrochloric acid to adjust pH of each solution in various values. 
     Each of the solutions different in pH value was aseptically charged in a glass vial to seal the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin-Hse and amount of [Leu 13  ]-motilin-Hse-lactone formed by modification of Hse residue at 23-position of the former were measured with HPLC method to check the relation with the pH value of the solution. 
     Results are shown in following Table 3 and FIG. 2. 
     
                       TABLE 3______________________________________pH value   Remaining amount (%)*                    Formed amount (%)**______________________________________3.0     15.6             30.24.0     64.3             18.74.5     64.3             8.75.0     61.3             5.55.5     62.0             1.96.0     60.8             06.5     46.6             07.0     33.0             08.0     8.1              09.0     7.3              0______________________________________ In Table 3, *Remaining amount of [Leu.sup.13 ]-motilinHse, and **Amount of formed [Leu.sup.13 ]-motilinHse-lactone. 
    
     It is apparent from results shown in Table 3 the motilin analogue ([Leu 13  ]-motilin-Hse) can also be kept in a relatively stable state by setting pH value of the solution in a range of about 4.0-6.0, but modification into [Leu 13  ]-motilin-Hse-lactone will occur in the pH range of 5.5 or more less. 
     Example 2 
     Aqueous solutions, each containing 20 μg/ml of [Leu 13  ]-motilin-Hse and 30 mg/ml of tartaric acid were aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin-Hse and tartaric acid in a refined water and adding 0.1 N-sodium hydroxide and 0.1 N-hydrochloric acid to adjust pH of each solution in various values. 
     Each of the solutions different in pH value was aseptically charged in a glass vial to seal the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin-Hse and amount of [Leu 13  ]-motilin-Hse-lactone formed by modification of Hse residue at 23-position of the former were measured with HPLC method to check the relation with the pH value of the solution. 
     Results are shown in following Table 4 and FIG. 3. 
     
                       TABLE 4______________________________________pH value   Remaining amount (%)*                    Formed amount (%)**______________________________________3.0     15.8             29.74.0     65.3             16.84.5     70.7             6.45.0     73.6             2.75.5     72.8             1.56.0     73.5             06.5     74.1             07.0     71.0             08.0     65.3             09.0     45.9             0______________________________________ In Table 4, *Remaining amount of [Leu.sup.13 ]-motilinHse, and **Amount of formed [Leu.sup.13 ]-motilinHse-lactone 
    
     It is apparent from the results shown in Table 4 that in case of the motilin analogue ([Leu 13  ]-motilin-Hse), a pH range wherein the motilin analogue shows a stability expands to about 4.0-8.0, by adding the organic acid and the formation of [Leu 13  ]-motilin-Hse-lactone can be suppressed by setting pH value of the solution higher than 5.5. 
     Comparative Example 5 
     Aqueous solutions, each containing 20 μg/ml of [Leu 13  ]-motilin-Hse and 27.2 mg/ml of potassium dihydrogenphosphate were aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin-Hse and potassium dihydrogenphosphate in a refined water and adding 0.1 N sodium hydroxide and 0.1 N-hydrochloric acid to adjust pH of each solution in various values. 
     Each of the solutions different in pH value was aseptically charged in a glass vial to seal the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin-Hse and amount of [Leu 13  ]-motilin-Hse-lactone formed by modification of Hse residue at 23-position of the former were measured with HPLC method to check the relation with the pH value of the solution. 
     Results are shown in following Table 5 and FIG. 4. 
     
                       TABLE 5______________________________________pH value   Remaining amount (%)*                    Formed amount (%)**______________________________________3.0     10.1             31.14.0     61.8             17.54.5     63.4             9.35.0     60.9             5.75.5     58.9             2.16.0     55.1             06.5     35.2             07.0     21.7             08.0     5.3              09.0     4.1              0______________________________________ In Table 5, *Remaining amount of [Leu.sup.13 ]-motilinHse, and **Amount of formed [Leu.sup.13 ]-motilinHse-lactone. 
    
     It is apparent from the results shown in Table 5 that the motilin analogue ([Leu 13  ]-motilin-Hse) shows a relatively high stability in lower pH range, when the inorganic acid coexists, but in such lower pH range, the formation rate of [Leu 13  ]-motilin-Hse-lactone increases, so that the existence of the inorganic acid gives bad influence, when the motilin analogue should be stored under conditions with higher pH range. 
     Comparative Example 6 
     Aqueous solutions, each containing 20 μg/ml of [Leu 13  ]-motilin were aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin in a refined water and adding 0.1N-sodium hydroxide and 0.1N-hydrochloric acid to adjust pH of each solution in various values. 
     Each of the solutions different in pH value was aseptically charged in a glass vial to lyophilize the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin was measured with HPLC method to check the relation with the pH value of the solution. 
     Results are shown in following Table 6 and FIG. 5. 
     
                       TABLE 6______________________________________pH value Remaining amount of [Leu.sup.13 ]-motilin (%)______________________________________3.0      25.64.0      62.54.5      70.45.0      66.35.5      65.66.0      52.76.5      44.17.0      35.88.0      17.89.0      15.3______________________________________ 
    
     It is apparent from the results shown in Table 6 that it is preferable to lyophilize the solution prepared by setting its pH value to about 4.0-5.5, and that the lyophilized powder is more stable than the aqueous solution, by comparing the results with those given in Comparative Example 3 (Table 2, FIG. 1). 
     Comparative Example 7 
     Aqueous solutions, each containing 20 μg/ml of [Leu 13  ]-motilin-Hse were aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin-Hse in a refined water and adding 0.1N-sodium hydroxide and 0.1N-hydrochloric acid to adjust pH of each solution in various values. 
     Each of the solutions different in pH value was aseptically charged in a glass vial to lyophilize the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin-Hse and amount of [Leu 13  ]-motilin-Hse-lactone formed by modification of Hse residue at 23-position of the former were measured with HPLC method to check the relation with the pH value of the solution. 
     Results are shown in following Table 7 and FIG. 6. 
     
                       TABLE 7______________________________________pH value   Remaining amount (%)*                    Formed amount (%)**______________________________________3.0     24.4             25.14.0     61.8             16.94.5     67.0             7.35.0     68.5             3.95.5     65.7             1.86.0     49.3             06.5     40.0             07.0     37.6             08.0     20.3             09.0     16.8             0______________________________________ In Table 7, *Remaining amount of [Leu.sup.13 ]-motilinHse, and **Amount of formed [Leu.sup.13 ]-motilinHse-lactone. 
    
     It is apparently seen from the results shown in Table 7 that the motilin analogue ([Leu 13  ]-motilin-Hse) shows a relatively high stability in a pH range of about 4.0-5.5, but [Leu 13  ]-motilin-Hse-lactone will be formed in the pH range of 5.5 or more less, and the amount thereof is somewhat less than that in the liquid state. This means that sufficient stability of [Leu 13  ]-motilin-Hse can not be secured by lyophilization only. 
     Example 3-6 and Comparative Example 8 
     Aqueous solutions, each containing 20 μg/ml of [Leu 13  ]-motilin-Hse and a following additive were aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin-Hse and the additive in a refined water and adding 0.1N-sodium hydroxide and 0.1N-hydrochloric acid to adjust pH of each solution to 6.0 or 7.0. 
     Each of the solutions was aseptically charged in a glass vial to lyophilize the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin-Hse and amount of deamide compound which was formed by modification of asparagine (Asn) residue at 19-position of the motilin analogue ([Leu 13  ]-motilin-Hse) were measured with HPLC method to check the relation with the pH value of the solution. 
     
         ______________________________________   Additive   Concentration (mg/ml)______________________________________Control   --           --Comparative     KH.sub.2 PO.sub.4                  27.2Example 8Example 3 Asp (Na)     31.0Example 4 Tartaric acid                  30.0Example 5 Sodium acetate                  16.4Example 6 Sodium lactate                  22.4______________________________________ 
    
     Results are shown in following Table 8. 
     
                       TABLE 8______________________________________   Remaining amount (%)*                 Formed amount (%)**   pH 6.0  pH 7.0    pH 6.0    pH 7.0______________________________________Control   49.3      37.6      50.2    60.9Comp. Ex. 8     35.2      28.5      63.1    69.8Example3         94.1      93.8      5.8     6.04         93.8      93.2      6.0     6.55         92.1      91.8      7.8     8.26         91.9      91.2      8.0     8.5______________________________________ In Table 8, *Remaining amount of [Leu.sup.13 ]-motilinHse, **Amount of formed deamide compound. 
    
     As apparent from the results shown in Table 8, it has been found that the organic acid and salt thereof effectively suppress the modification in asparagine residue at 19-position in about neutral pH range to stabilize the motilin analogue ([Leu 13  ]-motilin-Hse), and while, coexistence of the inorganic acid unstabilize the motilin analogue. 
     Comparative Example 9-16 
     Aqueous solutions, each containing 20 μg/ml of [Leu 13  ]-motilin-Hse and an additive (following saccharide or amino acid) were aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin-Hse and the additive in a refined water, and adding 0.1N-sodium hydroxide and 0.1N-hydrochloric acid to adjust pH of each solution to 6.0 or 7.0. 
     Each of the solutions was aseptically charged in a glass vial to lyophilize the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin-Hse and amount of deamide compound which was formed by modification of asparagine (Asn) residue at 19-position of the motilin analogue ([Leu 13  ]-motilin-Hse) were measured with HPLC method to check the relation with the pH value of the solution. 
     
         ______________________________________      Additive Concentration (mg/ml)______________________________________Control      --         --Comparative Example 9           Mannitol   36.410           Inositol   36.011           Lactose    68.512           Maltose    68.513           Dextran 70 50.014           Glycine    15.015           Alanine    17.816           Arginine   34.8______________________________________ 
    
     Results are shown in following Table 9. 
     
                       TABLE 9______________________________________   Remaining amount (%)*                 Formed amount (%)**   pH 6.0  pH 7.0    pH 6.0    pH 7.0______________________________________Control   49.3      37.6      50.2    60.9Comp. Example 9        50.3      39.3      48.7    58.910        67.5      65.8      30.8    34.011        64.7      63.9      35.0    35.212        65.3      62.9      34.2    35.713        88.7      88.8      11.0    11.014        62.8      58.1      36.3    40.315        59.7      53.6      38.5    45.216        96.0      95.7      3.8     4.1______________________________________ In Table 9, *Remaining amount of [Leu.sup.13 ]-motilinHse, **Amount of formed deamide compound. 
    
     As apparent from the results shown in Table 9, it has been found that excepting arginine, the amino acid or saccharide per se can not sufficiently suppress the formation of deamide compound. In connection with this, please note that the results shown in Table 9 are on lyophilized powder, and that, in case of existing arginine in the solution, the remaining amount of [Leu 13  ]-motilin-Hse is 64.7% (pH 6.0) or 40.9% (pH 7.0) (see Comparative Example 2, Table 1). 
     Example 7-12 and Comparative Example 17 
     Aqueous solutions, each containing 20 μg/ml of [Leu 13  ]-motilin-Hse and following additive(s) were aseptically prepared by dissolving 1 mg of [Leu 13  ]-motilin-Hse and the additive(s) in a refined water, and adding 0.1N-sodium hydroxide and 0.1N-hydrochloric acid to adjust pH of each solution to 6.0 or 7.0. 
     Each of the solutions was aseptically charged in a glass vial to lyophilize the same. Each vial was stored in a constant temperature bath kept at 60° C. for 30 days and then a remaining amount of [Leu 13  ]-motilin-Hse and amount of deamide compound which was formed by modification of asparagine (Asn) residue at 19-position of the motilin analogue ([Leu 13  ]-motilin-Hse) were measured with HPLC method to check the relation with the pH value of the solution. 
     Control: 
     No additive, 
     Comparative Example 17: 
     KH 2  PO 4  (13.6 mg/ml)+Arg (34.8 mg/ml), 
     Example 7: 
     Asp Na (15.5 mg/ml)+Arg (34.8 mg/ml), 
     Example 8: 
     Asp Na (11.6 mg/ml)+Arg (26.1 mg/ml)+Mannitol (13.7 mg/ml), 
     Example 9: 
     Asp Na (11.6 mg/ml)+Arg (26.1 mg/ml)+Lactose (25.7 mg/ml), 
     Example 10: 
     Tartaric acid (15.0 mg/ml)+Arg (34.8 (mg/l), 
     Example 11: 
     Tartaric acid (11.3 mg/ml)+Arg (26.1 mg/ml)+Mannitol (13.7 mg/ml), and 
     Example 12: 
     Tartaric acid (11.3 mg/ml)+Arg (26.1 mg/ml)+Lactose (25.7 mg/ml). 
     
                       TABLE 10______________________________________   Remaining amount (%)*                 Formed amount (%)**   pH 6.0  pH 7.0    pH 6.0    pH 7.0______________________________________Control   96.0      95.7      3.8     4.1Comp. Ex. 17     89.2      87.8      10.5    12.0Example 7        99.9      98.7      0       1.1 8        100.9     97.9      0       1.8 9        99.5      98.3      0       0.510        100.2     101.3     0       011        99.8      99.7      0       012        102.0     99.8      0       0______________________________________ In Table 10, *Remaining amount of [Leu.sup.13 ]-motilinHse, **Amount of formed deamide compound. 
    
     As apparent from the results shown in Table 10, the stability of [Leu 13  ]-motilin-Hse can be increased, when the amino acid, or amino acid and saccharide coexist(s), in addition to an organic acid or salt thereof.