AU4278393A

AU4278393A - Lyophilized somatotropin formulations

Info

Publication number: AU4278393A
Application number: AU42783/93A
Authority: AU
Inventors: Henry E. Auer; Matthew H Hulbert; Carl W. Richey Jr.; James E. Seely
Original assignee: Mallinckrodt Veterinary Inc
Current assignee: Mallinckrodt Veterinary Inc
Priority date: 1992-04-07
Filing date: 1993-04-05
Publication date: 1993-11-08
Also published as: WO1993019773A1; CA2133737A1; JPH08502021A; CN1078910A; EP0639984A1; CN1089249C

Description

1yoph1.1zed somatotropin formulations

BACKGROUND OF THE INVENTION

The^" present invention relates to novel solutions of somatotropins which remain clear for an extended period of time and which remain clear when subjected to mechanical agitation, and to kits for making the solutions.

Somatotropins, also known as growth hormones, are polypeptide hormones secreted by the pituitary glands of many animal species. These hormones are valuable for a number of therapeutic uses, and compositions comprising somatotropin can be administered in the treatment of pituitary deficiency in humans and gastrointestinal bleeding or to promote the healing of bone fractures and accelerate the healing of contusions and other wounds. Somatotropins also are useful in promoting meat and milk production in animals when administered through various drug-releasing devices or by injection. (See E.J. Tur an, "Some Effects of Pituitary Anterior Growth Factor" Thesis: Purdue

University, April, 1953; L.J. Machlin, J. Ani . Sci. 35: 794-800 (1972); T.R. Kasser et al., J. Anim. Sci. 53: 420-426; L.J. Machlin, J. Dairy Sci. 56: 575-580 (1973)). It frequently is desirable to work with and administer proteins such as somatotropins in the form of a solution. However, dissolved proteins, such as somatotropin, can be adsorbed at hydrophobic interfaces, thus causing secondary reactions. For example, "denaturing", i.e. a change in the shape of the adsorbed somatotropin molecules can occur. In addition, aggregation of adsorbed somatotropin molecules can take place to give soluble or insoluble polymeric forms. This aggregation will manifest itself, for example, as turbidity of the solution or as biological inactivation of the somatotropin protein on stirring or shaking of the aqueous solutions (See A.F. Henson et al., J. Colloid Interface Sci. 32: 162 (1970)).

When the somatotropin precipitates from solution, the precipitated protein becomes unavailable for administration. Thus, a somatotropin solution is needed which will not become turbid upon stirring or shaking and which will remain clear over extended periods of storage.

Summary of the Invention

In accordance with the present invention, there are disclosed somatotropin solutions which remain clear for extended periods and which do not become cloudy or precipitate when subjected to mechanical agitation. The somatotropin solutions contain a lyophilized somatotropin composition containing about 1 part somatotropin per 2 to 8 parts arginine HCl on a weight basis, the pH of the composition prior to lyophilization within the range of about 7.2 to about 8.5, which is dissolved in a diluent. If the pH of the somatotropin composition prior to lyophilization was less than 7.8, the diluent comprises EDTA, a nonionic surfactant and a buffer. If the pH of the somatotropin composition prior to lyophilization was 7.8 or greater, the diluent comprises EDTA and a nonionic surfactant and optionally, further can comprise a suitable buffer or nonbuffering agent if desired. If a non-buffering agent is added, desirably a buffer is not also added to the diluent, although both agents can be used.

This invention further provides kits for making the solutions. The kits include a vial containing the lyophilized somatotropin composition containing about 1 part somatotropin per 2 to 8 parts arginine HCl on a weight basis. The kits also include a vial containing a biocompatible diluent comprising EDTA and a nonionic surfactant. In addition, as described above-, depending upon the pH of the somatotropin composition prior to lyophilization, the diluent also can comprise a buffer or non-buffering agent. If the pH of the somatotropin composition prior to lyophilization was less than 7.8, the vial containing the diluent further comprises a buffer. At a pH of 7.8 or greater the vial optionally can contain a buffer or nonbuffering agent. The diluent can be added to the lyophilized somatotropin composition and the resultant mixture then shaken to dissolve the somatotropin.

Detailed Description of the Invention

This invention is directed to somatotropin solutions which remain clear for extended periods and which do not become cloudy or precipitate when subjected to mechanical agitation such as shaking or vortex-mixing. A somatotropin solution which remains "clear" is a solution in which the somatotropin does not precipitate after it is dissolved in the diluent. These somatotropin solutions will remain clear after several days of storage, typically at least about 5 days. The somatotropin solutions maintain clarity for at least about 5 days when stored, typically, for example, at about 25°C. At slightly higher storage temperatures, the somatotropin solutions maintain clarity, but possibly for a shorter period of time. A solution which remains clear will have an apparent absorbance measurement at 360 n (O.D. 360) of less than 0.10. The somatotropin solutions contain a lyophilized somatotropin composition, the pH of which prior to lyophilization was at least about 7.2, generally within the range of from about 7.2 to about 8.5. If the pH of the somatotropin composition prior to lyophilization was ^"less than 7.8, the diluent comprises EDTA, a nonionic surfactant and a suitable buffer to stabilize the final somatotropin solution. If the pH of the somatotropin composition prior to lyophilization was 7.8 or higher, the diluent comprises EDTA and an nonionic surfactant and, optionally, a buffer or nonbuffering agent. If a non-buffering agent is added to the diluent, desirably a buffer is not also added to the diluent, although both agents can be used. Neither the buffer nor nonbuffering agent need be used if the pH of the_. somatotropin composition prior to lyophilization was at least 7.8, but either can be provided to adjust or maintain the isotonicity of the resultant somatotropin solution such that it is less hypertonic. This is desirable if the somatotropin solution will be injected into animals. The choice of a suitable additive can be made based on a number of factors, including, for example, cost, presence on the FDA GRAS list, autoclavability, chemical stability, lack of interaction with the somatotropin and bioco patibility.

The lyophilized somatotropin composition is prepared by dissolving arginine HCl with somatotropin, adjusting the pH of the solution to at least 7.2, preferably from 7.2 to 8.5, and removing any undissolved material by filtration or centrifugation. The somatotropin and arginine HCl solution then is lyophilized using standard procedures known in the art. The solution to be lyophilized generally contains about 1 part somatotropin per 2 to 8 parts arginine HCl on a weight basis and preferably comprises about 1 part somatotropin per 3 parts arginine HCl. Thus, the solution preferably contains 10 to 150 mg/ml somatotropin and 30 to 450 mg/ml arginine HCl and has a final pH of at least 7.2. Most preferably, the solution to be lyophilized contains 30 mg/ml somatotropin and 90 mg/ml arginine HCl and has a final pH of from 7.8 to 8.5. The somatotropin which may be employed in the lyophilized somatotropin composition of this invention can be any somatotropin, including natural or recombinant bovine, porcine, human, avian, ovine, or equine somatotropin. Preferably, the somatotropin employed is porcine somatotropin. As used herein, the term somatotropin is intended to include the full length natural or recombinant somatotropin as well as derivatives thereof that have growth-promoting capabilities. Derivatives include biologically active fragments or analogs >of the polypeptide hormone, such as delta 7 porcine somatotropin, which has an amino acid sequence corresponding to that of porcine somatotropin, less the first seven amino acids of the mature, full length hormone (described in European Patent Application Publication No. 0 104 920 to Biogen N.V. ) . The term "biologically active" as used herein means a polypeptide that, following its administration to a living being, has a demonstrable effect on a biological process of that living being.

The somatotropins employed in the compositions of this invention can be metal-associated somatotropins. Metal-associated somatotropin is produced by the addition of salts of transition metals to an aqueous solution containing the somatotropin. The salts of the transition metals form insoluble complexes with the somatotropin, thus precipitating the somatotropin out of the solution. The metal-associated somatotropins comprise the somatotropin molecules and metal ions such as Zn⁺², Cu⁺², Co⁺², Mn⁺², Fe⁺² or Fe⁺³. These metal- associated somatotropins contain ligand bonds between the metal ion and the nitrogen atoms of some of the amino acid residues in the somatotropin molecule. The metal-associated somatotropins are used as starting materials for making the lyophilized somatotropin compositions. The metals likely are not associated with the somatotropin once the metal-associated somatotropin is lyophilized, although they are present in the lyophilized somatotropin composition. The presence of the transition metal in the product has been shown to have no significant adverse effect on the bioactivity of the somatotropin when the product is administered to a living being.

The somatotropin solutions of this invention are made by dissolving the lyophilized somatotropin composition with a diluent such that the pH of the final solution is at least about 7.2, typically from about 7.2 to about 8.5, and preferably from about 7.2 to about 8.2. If the pH of the solution is greater than about 8.5, ^"degradation of the protein can occur. Typically, about 0.5 to about 40 mg lyophilized somatotropin composition are provided per ml of diluent. Preferably, the final concentration of the somatotropin solution is about 10 to 30 mg lyophilized somatotropin composition per ml of diluent and most preferably about 20 mg lyophilized somatotropin composition per ml of diluent. The weight of the lyophilized somatotropin composition will be the total of the weight of the arginine HCl and the weight of the somatotropin contained in the lyophilized somatotropin composition.

If the pH of the somatotropin composition to be used in making the somatotropin solution was less than 7.8 prior to lyophilization, the diluent comprises EDTA, a nonionic surfactant and a buffer. Alternatively, if the somatotropin composition had a pH of at least 7.8 prior to lyophilization, the diluent comprises EDTA and a nonionic surfactant and optionally also comprises a buffer or nonbuffering agent. If the diluent comprises a buffer, the pH of the final somatotropin solution will be the same as the pH of the diluent. However, if the diluent is not buffered, the pH of the lyophilized somatotropin composition dissolved in the diluent will determine the pH of the final somatotropin solution.

Desirably, when the pH of the final somatotropin solution is between about 7.2 and about 7.6, the concentration of EDTA provided in the diluent is at least 1.5 mM, and is preferably from about 1.5 mM to about 10 mM. When the final somatotropin solution pH is greater than 7.6, the concentration of EDTA used in the diluent desirably is at least 1.0 mM, and is preferably from about 1.0 mM to about 10 mM. Surfactants which are suitable for use in the diluent include polyoxyethylene-23 lauryl ether (Brij 35), Tween 80, polyoxyethylene-20 cetyl ether (Brij 58), and other polyoxyethylene nonionic surfactants having similar hydrophilic/hydrophobic balance (HLB). Such nonionic surfactants have been noted in the prior art as stabilizing and preserving activity in purified enzymes. (See T. Kitani et al., Eur. J. Biochem. 119: 177-181 (1981); M. Pritchard et al., Biochem. Biophvs. Res. Commun. 100: 1597-1603 (1981); Seely et al.. Biochemistry, Vol. 21, No. 14, 3394-3399 (1982)). Generally, the surfactant is present in a concentration ranging from about 0.08% to 2.0%. If the surfactant utilized is Brij 35, the concentration of the Brij 35 is at least 0.08%, and preferably is from about 0.1% to about 0.2%. If the surfactant is Tween 80 or Brij 58, the concentration preferably is from about 0.1% to about 1.0%.

If the pH of the somatotropin prior to lyophilization was at least 7.2 but less than 7.8, a buffer is provided in the diluent to increase the stability of the somatotropin solution. The buffer can be Tris HCl, phosphate, or some other neutral, host- compatible pH buffer. Generally, the buffer is present in a concentration ranging from about 0.2 M to about

0.5 M. If Tris HCl is utilized as the buffer, the Tris HCl generally has a concentration of at least 0.2 M, and is preferably from about 0.2 M to about 0.3 M.

If the pH of the somatotropin composition prior to lyophilization was at least about 7.8, either a buffer as described above or a non-buffering agent can be added to the diluent, if desired, to adjust or maintain the isotonicity of the resultant somatotropin solution. The non-buffering agent also is host-compatible. Such agents include sucrose, trehalose, or NaCl. The non- buffering agent, if present, generally is provided at a concentration from about 0.05 M to about 0.5 M. When sucrose or trehalose is utilized as the non-buffering agent, preferred concentrations are within the range of from about 0.1 to about 0.3 M. When NaCl is utilized as the non-buffering agent a concentration of from 0.05 M to 0.15 M generally is preferred.

The somatotropin compositions of this invention can be made using kits containing a vial of the lyophilized somatotropin composition as discussed above and a vial containing the diluent discussed above. The diluent can be added to the lyophilized somatotropin composition and the resultant product shaken to dissolve the somatotropin.

The somatotropin solutions of this invention can be used for further processing or can be administered directly to animals. The solution generally can be stored for at least about 5 days at ambient temperatures, typically about 25°C, without becoming cloudy. The solutions also can be stored at slightly higher temperatures, although the solutions may maintain their clarity a shorter period of time. These solutions also can be subjected to mechanical agitation, such as shaking or mixing, without precipitation of the somatotropin from the solution. The somatotropin in these solutions maintains its biological activity and can be administered to animals in accordance with conventional techniques to promote growth.

The invention is further illustrated by the following examples, which are not intended to be limiting. Examples

In the following examples, solution clarity was determined by visual inspection and/or by measuring the apparent absorbance at 360 nm (O.D. 360); a wavelength where somatotropins have no intrinsic absorbance. The somatotropin solution was placed in the sample cuvette and the O.D. 360 determined using a Shimadzu UVU160 spectrophotometer. A diluent solution which did not contain somatotropin was used in the reference cuvette. Quartz cuvettes were used in all studies. In the examples described, "clear" solutions are those which have an O.D. 360 of less than 0.10.

Example 1 Thirty-three grams of Zn-associated porcine somatotropin (pST), made in accordance with the procedures disclosed in published European Patent Application No. 83300803.9, and 90 grams of arginine HCl were dissolved in one liter of sterile water. The pH was adjusted to 7.8 by the addition of aqueous HCl or NaOH and insolubles were removed by filtration through a polyvinylidene difluoride membrane. The clarified solution then was lyophilized. The resulting formulation (termed the "lyophilized porcine somatotropin (pST) composition") contained approximately 30 g pST per 90 g arginine HCl, due to the loss of about 10% of the original 33 g of pST as insoluble during the filtration step.

Example 2 Solid arginine HCl (1.92 g) was added to a non-Zn complexed pST solution containing 0.639 g pST in 21.6 ml of a pH 9.8, 0.46 mM sodium carbonate buffer. The arginine was dissolved by stirring and the pH of the solution was adjusted to 7.8 by the dropwise addition of 1 M NaOH. The resulting solution contained approximately 30 mg/ml pST and 90 mg/1 arginine. 5 Aliquots (7.2 ml) of this solution were pipetted into three 50-ml vials, frozen at -80°C, and lyophilized.

This lyophilized pST composition readily dissolved in 200 mM Tris HCl, 2 mM EDTA, 0.15% Brij 35 (pH 7.8) at 20 mg/ml (dissolution time < 3 minutes). The 0 resulting solution was clear by visual inspection.

Example 3

The following solutions were prepared:

1. 0.2 M Tris HCl, 2 mM EDTA, 0.15% Brij 35, pH 7.8 C O II II II II II it pH 7.4

3. 2 mM EDTA, 0.15% Brij 35, pH 7.8

Zinc-associated pST (Zn-pST), non-metal complexed pST (non-Zn pST) and the lyophilized pST composition 0 (made as described in Example 1) were dissolved by shaking for 2 minutes in each of the above solutions 5 mg/ml pST (or 20 mg/ml of the lyophilized pST composition). After the 2 minute shaking, solution clarity was determined by visual observation arid by 5 measuring turbidity at 360nm. As shown in Table 1, - only the lyophilized pST composition gave a clear solution after dissolution under these conditions. The results are shown in Table 1. Table 1

PST SOLUTION OD360

Zn-pST #1 0.522 #2 0.504 #3 0.381 non-Zn pST #1 0.242

#2 0.347 #3 0.186 lyophilized pST composition #1 0.019

#2 0.019 #3 0.019

Example 4

The following diluent solutions were made up:

2 mM

EDTA pH 7.8 containing

Forty mg aliquots of lyophilized pST composition (made as described in Example 1) were weighed out into seven 13 X 100 test tubes and dissolved in 2 ml of each of the above diluents. The solutions then were subjected to mechanical agitation by vortexing on a Vortex-Genie mixer for 30 seconds at a setting of 4.5. Solution clarity was determined by visual inspection by O.D. 360. The results are shown on Table 2. Table 2

Effect of various diluents on mechanical stability of reconstituted pST

Diluent Solution No.

.1 2 3 4 5 6 7 * si. cloudy = slightly cloudy; v. cloudy = very cloudy As shown in Table 2, the somatotropin solutions containing a Brij 35 concentration of at least 0.08% resulted in a clear solution after vortexing the lyophilized pST composition in the diluent under these conditions. The somatotropin solutions containing a

Brij 35 concentration of less than 0.08% did not remain clear following mechanical agitation by vortex mixing.

Example 5 Forty mg aliquots of lyophilized pST composition were weighed into 2 dram glass vials and dissolved in the diluent containing 200 mM Tris HCl, 0.10% Brij 35 at the following EDTA concentrations and final pH:

These samples were then placed in a 25°C constant temperature chamber and checked for visual clarity at various time points. Results are shown in Table 3.

Table 3

Effect of various diluents on solution stability of reconstituted pST

si. cloudy = slightly cloudy v. cloudy = very cloudy

As demonstrated in Table 3, somatotropin solutions, with a pH from 7.2 to 7.6, containing an

EDTA concentration of at least 1.5 mM resulted in a clear solution for at least 10 days after dissolution of the lyophilized pST composition in the diluent under these conditions. Further, somatotropin solutions with a pH of 7.6 or greater, containing an EDTA concentration of at least 1.0 mM, resulted in a clear solution for at least 5 days after dissolution of the lyophilized pST in the diluent under these conditions.

Example 6 Forty mg aliquots of lyophilized pST composition were weighed into 16 two-dram glass vials. Two ml of the following diluents were added: 1. 300 mM Tris HCl, 0.15% Brij 35, 1.5 mM EDTA, pH 7.4

2. 200 mM Tris HCl,

3. 100 mM Tris HCl,

4. 50 mM Tris HCl,

5. 25 mM Tris HCl,

6. 200 mM Tris HCl, 2.0 mM EDTA, pH 7

7. 1.5 mM EDTA,

8. 1.0 mM EDTA,

9. 10% sucrose, 0.15% Brij 35 mM EDTA

10. 5% sucrose,

11. 1% sucrose,

12. 0.2 M NaCl, 0.15% Brij 35 2 mM EDTA

13. 0.1 M NaCl,

14. 0.0 M NaCl,

The final pH of the samples after reconstitution with diluents 9-14 was ~7.8-7.9 (or approximately equal to the final adjusted pH of the pST/Arg solution just prior to lyophilization) . These samples were incubated in a 25°C constant temperature chamber for six days after which turbidity (O.D. 360 nm) readings were taken. Results are shown in Table 4.

Table 4

Effect of various diluents on solution stability of reconstituted pST

As demonstrated by solutions 1-5 in Table 4, a Tris HCl concentration of at least 200 mM must be employed in a diluent containing 0.15% Brij 35 and 1.5 mM EDTA at a pH of 7.4 in order for the somatotropin solution to remain clear for six days. Solutions 6-8 in Table 4 illustrated that an EDTA concentration of at least 1.5 mM was necessary, in addition to a Brij 35 concentration of 0.15% and a Tris HCl concentration of 200 mM at a pH of 7.2, in order for the somatotropin solution to remain clear for six days. As demonstrated by solutions 9-14, the somatotropin solution remained clear after six days when the diluent comprised 0.15% Brij 35, 2 mM EDTA and either 1%, 5%, or 10% sucrose or 0.2 M, 0.1 M or 0.0 M NaCl and the final pH of the samples were approximately 7.8-7.9.

Claims

We claim

1. A somatotropin solution which remains clear for extended periods and when subjected to mechanical agitation comprising a lyophilized somatotropin composition comprising about 1 part somatotropin per 2 to 8 parts arginine HCl on a weight basis, the pH of which was about 7.2 to about 8.5 prior to lyophilization, which is dissolved in a diluent comprising EDTA, a nonionic surfactant, and, if the pH of the somatotropin composition prior to lyophilization was between 7.2 and 7.8, a buffer.

2. The somatotropin solution of claim 1, wherein the pH of the somatotropin composition prior to lyophilization was at least 7.8 and the diluent further comprises a host compatible non-buffering agent.

3. The somatotropin solution of claim 1, wherein the pH of the somatotropin composition prior to lyophilization was at least 7.8 and the diluent further comprises a host-compatible buffer.

4. The somatotropin solution of claim 1, 2, or 3 wherein the somatotropin is natural or recombinant bovine, porcine, human, avian, ovine, or equine somatotropin or a bioactive fragment or analog thereof.

5. The somatotropin solution of claim 4 wherein the somatotropin is pST.

6. The somatotropin of claim 5 wherein the pST is delta 7 pST.

7. The somatotropin of claim 4 wherein the somatotropin is a metal associated somatotropin.

8. The somatotropin solution of claim 1, 2, or 3 wherein the nonionic surfactant is polyoxyethylene-23 lauryl ether (Brij 35), Tween 80, or polyoxyethylene- 20 cetyl ether (Brij 58) present in a concentration of from 0.08% to 2.0%.

9. The somatotropin solution of claim 8 wherein the nonionic surfactant is Brij 35 having a concentration of at least 0.08%.

10. The somatotropin solution of claim 9 wherein the nonionic surfactant is Brij 35 having a concentration of from about 0.1% to about 0.2%.

11. The somatotropin solution of claim 8 wherein the nonionic surfactant is Tween 80 or Brij 58 having a concentration of from about 0.08% to about 1.0%.

12. The somatotropin solution of claim 1 or 2 wherein the buffer is a neutral pH buffer present in a concentration of from 0.2 to 0.5 M.

13. The somatotropin solution of claim 12, wherein the buffer is Tris HCl or phosphate buffer.

14. The somatotropin solution of claim 13 wherein the buffer is Tris HCl having a concentration of from about 0.2 M to about 0.3 M.

15. The somatotropin solution of claim 3 wherein the concentration of the non-buffering component is from about 0.1 M to about 0.5 M.

16. The somatotropin solution of claim 15 wherein the non-buffering component is sucrose, trehalose, or NaCl.

17. The somatotropin solution of claim 1, 2, or 3 wherein the EDTA is present at a concentration of at least 1.5 mM if the pH of the somatotropin solution is less than 7.6, and is present in the diluent at a concentration of at least 1.0 mM if the pH of the somatotropin solution is at least 7.6.

18. A kit for making a somatotropin solution which remains clear when subjected to mechanical agitation and which does not become cloudy for extended periods, comprising a vial containing a lyophilized somatotropin composition which comprises about 1 part somatotropin per 2 to 8 parts arginine HCl on a weight basis, wherein the pH of said somatotropin composition prior to lyophilization was within the range of about 7.2 to about 8.5; and a vial containing a diluent comprising EDTA, a nonionic surfactant, and, if the pH of the somatotropin composition prior to lyophilization was between 7.2 and 7.8, a buffer.

19. A kit in accordance with claim 18, wherein the pH of the somatotropin composition prior to lyophilization was at least 7.8 and the diluent further comprises a biocompatible non-buffering agent.

20. A kit in accordance with claim 18, wherein the pH of the somatotropin composition prior to lyophilization was at least 7.8 and the diluent further comprises a host-compatible buffer.

21. A kit in accordance with claim 18, 19, or 20 wherein from about 0.5 mg to about 40 mg lyophilized somatotropin composition is provided per ml of diluent.

22. A kit in accordance with claim 18, 19, or 20 wherein the somatotropin is natural or recombinant bovine, porcine, human, avian, ovine, or equine somatotropin or a bioactive fragment or analog thereof.

23. A kit in accordance with claim 18, 19, or 20 wherein the surfactant is polyoxyethylene-23 lauryl ether (Brij 35), Tween 80, or polyoxyethylene-20 cetyl ether present in a concentration from 0.08% to 2.0%.

24. A kit in accordance with claim 18 or 20 wherein the buffer is Tris HCl, phosphate, and is present in a concentration of from 0.2 M to 0.5 M.

25. A kit in accordance with claim 19 wherein the non-buffering component is sucrose, trehalose or NaCl having a concentration of from about 0.1 M to about 0.5 M.

26. A process for making a somatotropin solution which remains clear when subjected to mechanical agitation and which remains clear for extended period which comprises the steps of: (1) preparing a lyophilized somatotropin composition by dissolving arginine HCl with somatotropin in an amount such that there is 1 part somatotropin per 2 to 8 parts arginine HCl, adjusting the pH to within the range of about 7.2 to about 8.5, removing any undissolved material by filtration or centrifugation, and lyophilizing the resultant solution; and

(2) dissolving the resulting lyophilized somatotropin composition in a diluent comprising EDTA and a nonionic surfactant, wherein, if the pH of the somatotropin composition prior to lyophilization was between about 7.2 and about 7.8, the diluent further comprises a buffer.

27. A process in accordance with claim 26, wherein the pH of the somatotropin composition prior to lyophilization was at least 7.8 and the diluent further comprises a biocompatible non-buffering agent having a concentration within the range of about 0.1 M to about 0.5 M.

28. A process in accordance with claim 26, wherein pH of the somatotropin composition prior to lyophilization was at least 7.8 and the diluent further comprises a neutral, host-compatible buffer present in a concentration within the range of about 0.2 M to about 0.5 M.

29. A process in accordance with claim 26 or 28, wherein the buffer is Tris HCl or phosphate buffer.

30. A process in accordance with claim 27, wherein the non-buffering component is sucrose, trehalose or NaCl.

31. A process in accordance with claim 26, 27, or 28 wherein the somatotropin is natural or recombinant bovine, porcine, human, avian, ovine, or equine somatotropin or a bioactive fragment or analog thereof.

32. A process in accordance with claim 26, 27, or 28 wherein the nonionic surfactant is polyoxyethylene-23 lauryl ether (Brij 35), Tween 80, or polyoxyethylene-20 cetyl ether present in a concentration from 0.08% to 2.0%.

33. A method for promoting growth which comprises administering a growth-promoting amount of a somatotropin solution which comprises a lyophilized somatotropin composition comprising about 1 part somatotropin per 2 to 8 parts arginine HCl on a weight basis, wherein the pH of the somatotropin composition prior to lyophilization was about 7.2 to about 8.5, dissolved in a diluent comprising EDTA, a nonionic surfactant, and, if the pH of the somatotropin composition prior to lyophilization was less than about 7.8, a buffer.

34. A method for promoting growth which comprises administering a growth-promoting amount of a somatotropin solution which comprises a lyophilized somatotropin composition comprising about 1 part somatotropin per 2 to 8 parts arginine HCl on a weight basis, wherein the pH of the somatotropin composition prior to lyophilization was about 7.2 to about 8.5, dissolved in a diluent comprising EDTA, a nonionic surfactant, and, if the pH of the somatotropin prior to lyophilization was at least 7.8, optionally further comprising a buffer or non-buffering agent.