A BUFFERED POLYOL-HORMONE MIXTURE FOR USE IN CHRONIC PARENTERAL HORMONE ADMINISTRATION

Abstract: A method of preventing the precipitation of proteins, such as hormone preparations, within drug delivery systems that depend on the fluidity of the infusate for proper function while extending and maintaining the biological activity of the protein during its period of storage in the drug delivery system. A polyol, such as glycerol, is mixed with the protein solution prior to the introduction of the solution into the drug delivery system. The polyol isadded in amount between about 10 and 90 per cent by volume sufficient to prevent precipitation of the protein during long-term storage in the drug delivery device. A physiologically compatible buffer system in concentration between about 1 mMolar and 1000 mMolar sufficient to maintain the pH of the solution within about one unit of the optimum pH of the protein is added to maintain the bioactivity of the protein during its extended period of storage. According to one form of usage, the protein-polyol-buffer solution is injected to the pressurized drug storage reservoir of an implanted infusion pump by injection through the patient's skin. As the solution is discharged from the delivery device by the constant pressure exerted upon the storage chamber, its low rate of flow is controlled by a restricted fluid passage. The solution is conveyed to an infusion site and diluted by the blood stream.

Description: A BUFFERED POLYOL-HORMONE MIXTURE FOR USE IN CHRONIC PARENTERAL HORMONE ADMINISTRATION FIELD OF THE INVENTION BACKGROUND OF THE INVENTION This invention relates to a method of maintaining and extending the bioactivity, while preventing pre¬ cipitation, of proteins, such as hormone prepara¬ tions, within drug delivery systems that depend on the fluidity of the infu.sate for proper function. One sys- tem of this type is the implantable infusion pump illustrated and described in Blackshear et al U. S. Patent No. 3,731,681, the disclosure of which is incor¬ porated herein by reference. In U. S. Patent No. 4,439,181, issued March 27, 1984, of common ownership herewith, it is disclosed that the addition of a pol¬ yol, such as glyσerol, increases the solubility of the protein (i.e., a hormone, such as insulin) in water ' without affecting its biological activity. The polyol solubilizes both native or denatured proteins and inhibits the action of precipitation agents, such as adverse temperatures. The disclosure of U. S. Patent No. 4,439,181 is incorporated herein by reference. . The control of many cellular functions in an organism is via hormones, such as insulin, human growth hormone, glucagon, and the like, secreted in very small amounts by specific glands into the blood stream. These hormones have high affinity for specific sites on or in the membranes of the specific cells. The hormones are typically small proteins with a marginal solubility in blood. The hormone is functionally active in the hydrophobic lipid membrane. A typical hormone deficiency disease is diabetes where the beta cells in the pancreas have been destroyed or are rela¬ tively ineffective, and the medical treatment is the administration of insulin. OMPI W WIIPPOO Recent studies have suggested that management of blood glucose in diabetics can be improved by admin¬ istering insulin by pump on a continuous basis, or in pulses several minutes apart, rather than by intermit- tent injections as is now common practice. One factor limiting the length of time this kind of administration can. be maintained has been precipitation of insulin in the flow passages of these pumps causing flow stoppage. The solution of this major problem has been the sub- ject of intensive research by several different organi¬ zations and groups. A further requirement of drug diluting fluids not necessarily related to nonprecipitability is stable bioavailability. A practical insulin diluting fluid suitable for an implantable drug pump must demonstrate no appreciable loss in bioactivity after one or more months of storage at body temperature in the pump drug reservoir.' Data accumulated since the filing of the applica- tion from which U. S. Patent No. 4,439,181 issued has further confirmed the effectiveness of the addition of a polyol, such as glycerol, in inhibiting the preci¬ pitation of hormones, such as insulin. However, there is evidence of partial loss of activity of the hormone over the extended period of time it remains in the drug delivery device. The lowering of biological activity is believed to be a time- and temperature-dependent propensity of the hormone to form soluble, higher molecular weight hormone polymers or oligomers. An alternative cause of loss of biological acti¬ vity may be due to molecular alteration of the hormone due to pH conditions. For instance, an insulin dilut¬ ing fluid that has a sufficiently alkaline pH may cause the cleavage of cystine sulfhydral linkages resulting in non-reversible loss of native tertiary structure. Although insulin does not generally preci¬ pitate as a consequence of such pH conditions (in fact OMPI solubility is enhanced) , the unfolding of the molecule and subseσuent random intermolecular and intramolecular reformation of the cystiene-σystiene bonds, results in a mixture of species with overall loss of bioactivity. It has now been discovered that formation of polymers may be prevented and biological activity over an extended time period may be maintained by the addition of phosphate buffer at neutral pH, along with sodium bicarbonate. THE PRIOR ART Albisser and colleagues (Albisser, A.M., et al: Diabetes 29:241, 1980) describe the use in their portable peristaltic pump of the addition of 1.5% autologous serum to prevent the precipitation and loss of insulin potency that occurred without serum. However, use of 1.5% serum in animal studies at Uni¬ versity of Minnesota Hospitals failed to prevent clog¬ ging of the capillary tubes of the pump of Patent No. 3,731,681 with insulin, possibly because of major differences in inner diameter between the capillary tubing of that pump and Albisser's delivery σannula. Dorman et al U. S. Patent No. 4,306,553 dis¬ closes that a surfactant, such as sodium lauryl sul- fate, will prevent the precipitation of insulin in the pump's delivery cannula. However, this compound has not yet been proven safe when used intravenously in man. Its effect on long term maintenance of bio¬ logical activity has not been determined. Lougheed et al (Insulin Aggregation in Artifi- cial Delivery Systems, Diabetologia 19:1-9, 1980) demonstrated that although sodium bicarbonate in con¬ centrations of at least 23 mMolar is a solubilizing agent for insulin crystals, including it in regular insulin solutions (either neutral insulin or its thiol derivative) does not prevent precipitates from forming in in vitro tests designed to mimic drug pump conditions. There is no disclosure of the effect of sodium bicarbonate on insulin bioactivity. SUMMARY OF THE INVENTION Broadly stated, this invention is directed to a method of maintaining the fluidity of protein solu- 5 tions for parenteral administration at a low flow rate to a chronically ill patient suffering from a protein-deficiency disease from an implanted pressure actuated drug delivery device without " loss of biologi¬ cal activity during the extended time period the solu- 0 tion is stored in the drug delivery device. A polyol, such as glycerol, is mixed with the protein solution prior to the injection of the solution into the drug storage chamber of the delivery device, for thorough dissolution and uniform distribution through the solu- 5 tion, along with a buffer to extend and maintain bio¬ activity of the drug. The polyol is added in an amount sufficient to prevent precipitation of the protein during long-term storage in the drug delivery device of up to several weeks. The buffer is added in 0 approximately physiologic concentrations. Thereafter, the protein-polyol-buffer solution is injected into the drug storage chamber by injection through the patient's skin. As the solution is discharged from the delivery device by the constant pressure exerted 5 upon the storage chamber, its low rate of flow is controlled by a restricted fluid passage. The solu¬ tion is conveyed to an infusion site by tubular pass¬ age means, -such as a small diameter catheter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT u According to the invention, a polyol solution, such as a solution of glycerol, is admixed with a solution of protein, such as a standard injectable hormone solution, so that the final concentration of polyol in the solution is from about 10 to 90% by ^ volume, and preferably about 40 to 80%, sufficient to prevent precipitation of the protein after charg¬ ing into the drug storage chamber of a pressure -< I__ actuated drug delivery device, such as the infusion pump of U. S. Patent No. 3,731,681. At the same time, to* extend and maintain -the biological activity of the protein during its period of storage in the drug delivery device, a small amount of a physiologically compatible buffer system is add¬ ed to the solution in concentration between about 1 mMolar and 1000 mMolar sufficient to maintain its pH within about 1 unit of optimum pH for the parti- cular protein. The optimum pH for sulfated insulin is 3.5; that for standard neutral insulin is 7.4. The objective is to avoid the isoelectric point of 5.4, which causes precipitation, and alkaline pH in the range of 8.0 and above, which is denaturing. The addition of a buffer capable of maintaining the pH in the desired range was found to reduce both poly¬ merization and loss of bioactivity. Whether this stabilizing effect is related to avoiding mechanisms associated with pH shifts " toward the isoelectric point or alkaline pH ' shifts is uncertain. However, samples with pH shifts in both directions have been prepared and polymerization has been detected in each case. Suitable buffers include the sodium phosphate, sodium bicarbonate, sodium acetate, sodium citrate, and other similar physiologically compatible buffer systems. In anticipation of eventual testing for clearance by the FDA for clinical intravenous use, the sodium phosphate buff r system at a pH of 7.4 (physiologic intravascular pH) in a concentration cur- - rently approved (54 mMolar, physiologic intracellular concentration) , in combination with 12 mM sodium bicarbonate, was selected for testing. The protein-polyol-buffer solution is injected into the drug storage chamber of the drug delivery device of a patient suffering from a protein-defici¬ ency disease. From the storage chamber the solution is discharged through a fluid restrictor at a low OMPI flow rate of from about 0.1 cc to 15 cc per day, de¬ pending upon the needs of the patient, and passed into the blood stream at the desired infusion site. Upon passage into the blood stream, the solution is immediately diluted to below about 0.15% by weight to rapidly return the protein to its normal state where it may function normally with no loss of activity. The invention is illustrated by the following examples: Example 1 Infusion of an insulih/glycerol/bicarbonate mix¬ ture in diabetic human subjects. In nine patients with Type II diabetes, infusion pumps (Infusaid TM Model 100, Infusaid Corporation, Norwood, MA) were implanted subcutaneously in the anterior chest wall, and the delivery cannulas were threaded into the super¬ ior vena cava via the subclavian vein in all cases. Two solutions were prepared. One contained 20 or 40 units per ml Neutral Regular porcine insulin (Lilly) , 0.2 per cent (w/v) phenol, 12 mM sodium bicarbonate and 80 per cent (v/v) glycerol. The other contained no insulin but also contained 0.2 per cent (w/v) phenol, 12 mM sodium bicarbonate and 80 per cent (v/v) glycerol. The two solutions were of identical viscosity. Immediately before use, the two solutions were combined in appropriate amounts to provide the appropriate final infusate insulin concentration. This procedure was found to be necessary because of the major alterations in pump flow rate that occur with minimal alterations in the viscosity of the 80 per cent glycerol solutions. No instances of pump occlusion or significant flow rate reductions have occurred after more than 460 patient-weeks of insulin/glycerol infusion in nine subjects in whom Model 100 pumps were implanted. Pump occlusion occurred in our first patient in whom a lower glycerol concentration was used in a Model 400 ■ * ΕEXT pump, which contains an auxiliary side port. The insulin delivered was clearly biologically active, as evidenced by the excellent glycemic control achieved. However, refill intervals of approximately 10 to 14 days were necessary due to a noticeable loss of bio- activity which was accompanied by changes of infusate pH toward the alkaline range above 8.0. The periods of infusion and pump flow*rates are shown in the table: Patient Weeks of Insulin Flow Rate (ml/day) Infusion Initial Final SJ 24 3.14 2.85 SM 34 3.00 3.00 NP 35 1.99 1.93 JP 35 2.28 2.00 NB 55 2.88 2.86 DN 67 3.42 3.21 DM 67 3.21 3.05 CS 69 3.50 3.50 CJ 74 1.53 1.42 Mean 51 2.77 2.64 Per cent change -5 per cent Total patient/weeks of infus ;ion: 460 Example 2 Effect of incubation of the insulin/glycerol/ biocarbonate mixture at various temperatures on insulin oligomer formation. To assess the effect of glycerol or other additives on the formation of high¬ er apparent molecular weight species of insulin (insulin oligomers) , the insulin/glycerol/bicarbon- ate mixture (40 units of insulin per ml) or insulin in regular insulin diluting fluid was incubated at 4°, 24° and 37° C in sterile glass vials for 0-4 weeks. In similar experiments, the insulin/glycerol/ bicarbonate mixture was incubated in sealed infusion pumps under the same conditions. Following each incu¬ bation a sample from each vial was prepared for elec- trophoresis under non-reducing conditions by the addi- tion of (final concentration) : 1.0 per cent (w/v) sodium dodecyl sulfate (SDS) , 3.3 per cent (w/v) sucrose; and .001 per cent (w/v) pyromin y. The samples were incubated at 37 C for 60 minutes, fol- lowing which 25 μl of sample (containing 0.8 units of insulin) was applied to the lanes of polyacrylamide slab gels prepared according to Laemmli (Nature, 1970; 227: 680-685) except that gels were cast of 20 per cent (w/v) acrylamide/2.67 per cent methylene-bis- acrylamide. Details of gel staining, destaining, densitometric scanning and protein molecular weight determination were as described by Blackshear et al (Biochem. J. , 1982; 204: 817-824). Occasionally, insulin/glycerol/bicarbonate solutions removed from the pumps after a normal flow cycle in the patient studies were subjected to electrophoresis in the same way. Finally, the effect of disulfide-bond reduction on insulin-polymer molecular weight was studied by adding 40 mM (final'concentration) dithiothreitol to the SDS electrophoresis buffer prior to the 37° C incubation. Incubation of the insulin/glycerol/bicarbonate mixture in glass vials at various temper;atu es for 4 weeks resulted in the temperature-dependent forma- tion of larger molecular weight species of insulin. By analysis using non-reducing electrophoresis, normal Neutral Regular porcine insulin (Lilly) contained approximately 2 per cent (by densitometry of stained protein) of a larger molecular weight species (about 7,300); this percentage increased only slightly after incubation at 37° C for one month. In contrast, the percentage of larger molecular weight forms of insulin increased markedly after incu¬ bation of the insulin/glycerol/bicarbonate mixture for one month at 0° C, 24° C or 37° C. In addition, several still larger molecular weight forms appeared after incubation with glycerol at 24° C and 37° C. The formation of larger molecular weight forms of insulin in the presence of glycerol occurred to an identical extent during parallel incubations in glass vials and sealed implantable infusion pumps. 5 The proportion of insulin in the form of higher molecular weight species increased as a function of both time and temperature in the insulin/glycerol/ bicarbonate mixture. At the end of four weeks of incubation in glass vials at 37° C, approximately 33 10 per cent of the insulin was in the form of higher molecular weight species. Insulin removed from pumps after two weeks in patients displayed similar changes, i.e., there were larger proportions of higher molecular weight forms. 15 When insulin previously incubated for four weeks at 37° C was subjected to electrophoresis under reduc¬ ing conditions, the largest form visible had a M slightly larger than native, unreduced insulin; in addition, large amounts of protein migrating near the 20 dye front, presumably free A and B chains, could be detected. Example 3 Effect of buffering with sodium bicarbonate or sodium phosphate on the extent of insulin oligomer 25 formation. After incubation in glass vials at 37 C for four weeks, sodium bicarbonate (12 mM) decreased the amount of insulin-polymer formation in 80 per cent glycerol when compared to insulin in glycerol without bicarbonate. Further addition of 54 mM sodium phos- 3 0 phate decreased the formation of polymers still further. The biological activity of this insulin/glycerol/ bicarbonate/phosphate mixture was tested in a dog previously made diabetic with alloxan according to the standard technique described by applicant and 35 colleagues (Surg. Gynecol. Obstet. , 1982; 155: 860-864). The insulin delivered intravenously in this animal from an implantable pump was either the insulin/ OMPI glycerol/biσarbonate mixture described above, or an identical solution containing in addition (final con¬ centration) 54 mM sodium phosphate, pH 7.0. To deter¬ mine whether the insulin actually delivered from the pump's infusion cannula retains biological activity during a three week flow cycle, the effects of alter¬ nating cycles of phosphate buffered and unbuffered insulin on fasting plasma glucose levels were compar¬ ed at insulin delivery rates of 22 units/day. The phosphate-buffered solutions clearly prevent¬ ed the gradual increase in fasting plasma glucose con¬ centrations that occurred late in a three week flow cycle without phosphate. The addition of bicarbonate and phosphate buffers to the insulin/glycerol mixture - appears to be largely effective in preventing the glycerol-induσed formation of presumably inactive insulin oligomers. * * * * * * * * Although the invention has been described-with particular reference to the use of glycerol, other biocompatible C-4 to C-18 polyols, including sugars, behave similarly to glycerol as protectors of protein structure and function. Exemplary of such other polyols are C-4: erythritol; C-5: arabinose, xylose, ribose, adonital (ribitol) and arabitol; C-6: rhamose, inositol, fructose, galactose, glucose, mannose and sorbose, C-12: maltose and sucrose; and C-18: melezi- tose and raffinose. Where solid polyols are used they are dissolved in the standard aqueous insulin solution, or first prepared as an aqueous solution and admixed with the insulin, to provide a final concen¬ tration of polyol in the solution of about 10 to 90% weight/volume, and preferably about 40 to 80%. Simi¬ larly, although the invention is described with parti¬ cular reference to solubilization of insulin, other infusible proteins are subject to the same precipi¬ tation problems, * including growth hormone, glucagon, es ι ςτ*T! _τ^ i?*2J. ?τ ^^URE -11- and the like . It is apparent that many modifications and varia¬ tions of this invention as hereinbefore set forth may be made without departing from the spirit and scope thereof. The specific embodiments described are given by way of example only and the invention is limited only by the terms of the appended claims. QMPI WIPO

Claims: CLAIMS 1. In the method of maintaining the fluidity of protein solutions for parenteral administration at a low flow rate to a chronically ill patient suffering from a protein deficiency disease from a drug delivery device that depends on the fluidity of the infusate for proper functioning which comprises dissolving in the protein solution an effective amount between about 40 and 90 per cent by volume, sufficient to prevent precipitation of the protein, of a polyol, and charg¬ ing the drug storage chamber of the drug delivery device with said protein-polyol solution, the improve¬ ment which comprises maintaining the biological acti¬ vity of the protein-polyol solution during extended periods of storage within the drug delivery device by adding to the solution prior to injection into the drug storage chamber of the delivery device a buffer system in concentration between about 1 mMolar and 1000 mMolar sufficient to maintain a pH within about one unit of the optimum pH of said protein. 2. A method according to claim 1 wherein said polyol is glycerol and said buffer system is sodium phosphate. 3. A method according to claim 2 wherein said polyol is glycerol and said buffer system is sodium phosphate in combination with sodium bicarbonate. 4. A method according to claim 2 wherein said protein is a hormone. 5. A method according to claim 4 wherein said hormone is insulin. 6. A method according to claim 1 wherein said drug delivery device is an implanted pressure actuated device whose storage chamber is charged by. injection of the protein-polyol-buffer solution through the skin of the patient. 7. In the method of administering a protein solu¬ tion at a low flow rate to a chronically ill patient suffering from a protein-deficiency disease which comprises dissolving in the protein solution an effec¬ tive amount between about 10 and 90 per cent by volume, sufficient to prevent precipitation of the protein, of a polyol, charging the drug storage chamber of a drug delivery device that depends on the fluidity of the infusate for proper functioning with the protein- polyol solution, continuously discharging the solution from the storage chamber through a restricted flow passage into the blood stream of the patient at a rate between about 1 σσ and 15 cc solution per day,, and diluting the solution with the blood stream as it enters the blood stream, the improvement which com¬ prises adding to the protein-polyol solution a buffer system in concentration between about 1 mMolar and 1000 mMolar sufficient to maintain a pH within about one unit of the optimum pH of said protein to maintain the fluidity of the solution without loss of biologi¬ cal activity during storage. 8. A method according to claim 7 wherein said polyol is glycerol and said buffer system is sodium phosphate. 9. A method according to claim 8 wherein said polyol is glycerol and said buffer system is sodium phosphate in combination with sodium bicarbonate. 10. A method according to claim 8 wherein said protein is a hormone. 11. A method according to claim 10 wherein said hormone is insulin. 12. A method according to claim 7 wherein said drug delivery device is an implanted pressure actuat¬ ed device whose storage chamber is charged by injec¬ tion of the protein-polyol-buffer solution through the skin of the patient. 13. In the method of maintaining the fluidity of insulin solutions for parenteral administration at a low flow rate to a chronically ill patient suf¬ fering from diabetes from a drug delivery device that depends on the fluidity of the infusate for proper functioning which comprises dissolving in the insulin solution an effective amount between about 40 to 90 per cent by volume, sufficient to prevent precipita¬ tion of the protein, of a polyol, and charging the drug storage chamber of the drug delivery device with said insulin-polyol solution, the improvement which com¬ prises maintaining the biological activity of the insulin-polyol solution during extended periods of storage within the drug delivery device by adding to the solution prior to injection into the drug storage chamber of the delivery device a sodium phosphate buffer system " in concentration between about 1 mMolar and 1000 mMolar sufficient to maintain a pH within about one unit of the optimum pH of said protein. 14. A method according to Claim 13 ' wherein said polyol is glycerol and said buffer system is sodium phosphate in combination with sodium bicarbonate. 15. A method according to claim 13 wherein said drug delivery device is an implanted pressure actuated device whose storage chamber is charged by injection of the insulin-polyol-buffer solution through the skin of the patient. 16. In the method of administering an insulin solution at a low flow rate to a chronically ill patient suffering from diabetes which comprises dis¬ solving in the insulin solution an effective amount between about 10 and 90 per cent by volume, suffici¬ ent to prevent precipitation of the insulin, of glycerol, charging the drug storage chamber of a drug delivery device that depends on the fluidity of the infusate for proper functioning with the insulin- glyσerol solution, continuously discharging the OMPI \A. WIPO solution from the storage chamber through a restricted flow passage into the blood stream of the patient at a rate between about 1 cc and 15 cc •solution -per day, and diluting the solution with the blood stream as it enters the blood stream, the improvement which com¬ prises adding to the insulin-glycerol solution a com¬ bination sodium phosphate-sodium bicarbonate buffer system in concentration between about 1 mMolar and 1000 mMolar sufficient to maintain a pH within about one unit of the optimum pH of said insulin to maintain the fluidity of the solution without loss of biologi¬ cal activity during storage. 17. A method according to claim 16 wherein said drug delivery device is an implanted pressure actuated device whose storage chamber is charged by injection of the insulin / glycerol-buffer solution through the skin of the patient. SUBSTITUTE SHEET

Inventors: WIGNESS BRUCE D, WIGNESS, BRUCE, D.
Applicants: UNIV MINNESOTA, REGENTS OF THE UNIVERSITY OF MINNESOTA
Application year: 1984
Main classification: A61K37
IPC codes: A61K9, A61K38, A61K47