IMPROVEMENTS IN OR RELATING TO DOBUTAMINE SALTS

Abstract: Certain hydroxyalkanoic or alkandioic acid salts of dobuta­ mine having desirable water solubility are useful in preparing in­ travenous solutions for treatment of cardiogenic shock.

Description: IMPROVEMENTS IN OR RELATING TO DOBUTAMINE SALTS Dobutamine, N-[3-(4-hydroxyphenyl)-1-methyl- propyl]-2-(3,4-dihydroxyphenyl)ethylamine is marketed as the hydrochloride salt. Its use as an ionotrope for treating cardiac insufficiency is disclosed in United States Patent No. 3,987,200. This U.S. patent discloses mineral salts of dobutamine, including the hydrochloride. Unfortunately, such salts of dobutamine are substantially insoluble in water. In accordance with the invention, it has now been discovered that salts of dobutamine formed with an acid of formula I: (OH)#####C2-11 alkyl##COOH)1-2 I are water-soluble and that pharmaceutical formulations containing such salts have improved stability characteristics. Examples of such acids include lactic acid, gluconic acid, lactobionic acid, glucoheptonic acid, glyceric acid, glycollic acid, tartaric acid, malic acid, mevalonic acid, dihydroxybutyric acid, dihydroxyisobutyric acid, dihydroxyvaleric acid, dihydroxy isovaleric acid, erythronic acid, threonic acid, bis(hydroxymethyl)malonic acid, 2, 3-dihydroxy glutaric acid, dihydroxyadipic acid, bis(hydroxymethyl) acetic acid and the like. Salts of dobutamine formed with optical isomers of the above acids are included within the scope of this invention. Dobutamine is a racemate of the following structure: EMI2.1 The a-carbon (marked with an asterisk) is asymmetric, yielding two stereoisomers, the (+) and the (-), which, in a 1:1 mixture, form the racemate. This invention includes soluble salts formed with acids of formula I of (+)-N-[3-(4-hydroxyphenyl)-l-methylpropyl]-2-(3,4- dihydroxyphenyl)ethylamine and of the corresponding (-) stereoisomer as well as of the racemate. It will be understood that the term dobutamine as used herein includes both the racemate and the stereoisomers. The soluble dobutamine salts of this invention can be prepared by direct neutralization of the amine base or by a metathetic reaction (double decomposition) involving an acid addition salt of dobutamine. The neutralization procedure is preferred. According to one aspect of the invention there is provided a process for preparing a soluble salt of dobutamine and an acid of formula: ( H)1-8(C2¯11 alkylitCOOH)1 I which comprises: (a) neutralizing dopamine as the free base with the acid of formula (I), or (b) the metathetic reaction of an acid addition salt of dobutamine with a salt of the acid of formula (I). In the neutralization procedure, dobutamine free base can be prepared by suspending dobutamine hydrochloride in oxygen-free water, adding an antioxidant (peroxide scavenger) followed by the addition of a dilute aqueous solution of a base (an inorganic base such as an alkali metal hydroxide, carbonate, bicarbonate etc. or a water-soluble organic base such as tris (hydroxymethyl)methylamine). Dobutamine base is waterinsoluble and separates as a white crystalline mass from the alkaline medium. The crystals are separated, as by filtration, and dried. The dried crystals are then added to oxygen free water containing an antioxidant. The desired acid (for salt formation) is added in slight excess as an aqueous solution, and the desired salt is formed. The salt solution can be stored for filing into vials where the solution is lyophilized or the salt solution can first be lyophilized and the lyophilized salt stored. All the above operations are carried out in an oxygen-free (insofar as practicable) atmosphere. A typical example of such a reaction sequence follows. Example 1 Preparation of Dobutamine Salts Seventeen grams of dobutamine hydrochloride were suspended in 500 ml of deaerated water [deaerated by alternatively applying a vacuum (10-100 Torr.) followed by a period of sparging with N2]. 150 mg of sodium sulfite were added as a peroxide scavenger. The suspension was stirred under a constant positive N2 pressure. 50 ml of 1N aqueous sodium hydroxide diluted to 120 ml with deaerated water were added in dropwise fashion over a 2.5 hr. period. After the addition was complete, the neutralization mixture was stirred for an additional 2 hours, during which time a white crystalline solid comprising dobutamine free base separated. The supernate was decanted, and the crystalline residue washed thoroughly with 600 ml of deaerated water. The supernate was again decanted. The solid precipitate was then filtered under N2. The filter cake was washed twice with 100 ml portions of water and was then dried at 450C under vacuum for 3 hours. 14.5 g of dobutamine free base were thus obtained. A repeat preparation was carried out on a 3x scale except that sodium bisulfite (0.5 g) was used in place of sodium sulfite; yield of dried crystalline dobutamine free base = 43.0 g (96%). 8.3 Millimoles of dobutamine free base and 8.7 millimoles of each of the following acids: glycolic, (+)-tartaric, gluconic, lactobionic and glucoheptonic, were mixed under an N2 atmosphere with an amount of 0.035 g aqueous sodium Disulfite dissolved in water for injection such that the final volume was 25 ml; i.e., 100 mg/ml of dobutamine base. If required, the saltforming mixture was warmed to expedite solution of dobutamine base. The solid salt can be obtained from the solution, if desired, by evaporation of the solvent. The solubilities of each of the dobutamine salts thus prepared was in excess of 100 mg/ml. By contrast, a saturated solution of dobutamine hydrochloride provides about 25 mg/ml of dobutamine. In a repeat with (-)-tartaric acid, 58.6 g of dobutamine hydrochloride in deaerated water were neutralized with dilute aqueous sodium hydroxide in the presence of a peroxide scavenger under N2; pH = 11.09. The precipitate of dobutamine base was washed with the aerated water and dried. The filter cake was dissolved in 2 1 of deaerated water followed by 26.1 g of (-)-tartaric acid and 0.8 g of sodium bisulfite; pH = 3.65. The solution was filtered and then stored at room temperature, always under an N2 atmosphere. Such stored concentrate solutions are stable for 12 months or more at SOC. A preferred method of preparing dobutamine free base involves the use of tris(hydroxymethyl)methylamine in place of aqueous sodium hydroxide. A typical preparation using this procedure is carried out as follows: 500 ml of deoxygenated water for injection (WFI) are placed in a 2 1 3-neck round-bottom flask equipped with N2 inlet, dropping funnel, stirring means and a probe leading to a pH meter. A nitrogen sweep is maintained throughout the operation. 50 mg of NaHSO3 are added and the mixture stirred till solu tion occurs. 80.16 g of dobutamine hydrochloride are added via a y-tube adapter, and any salt remaining in the addition tube is washed in with an additional 500 ml of deoxygenated water (WFI). The resulting slurry is stirred for 15-20 minutes. 250 ml of 1M aqueous tris (hydroxymethyl)methylamine [30.3 g in 250 ml of deoxygenated water (WFI)] are added in dropwise fashion over a 1-2 hr. period at such a rate that the pH of the solution does not rise above pH=8.5. After the addition is completed, the neutralization mixture is chilled to a temperature in the range 0-10 C. The chilled solution is then vacuum filtered under N2. The filter cake comprising dobutamine free base is washed with 1200 ml of deoxygenated water (WFI) (in three 400 ml portions). Next, a solution is prepared in a 2 1 beaker by dissolving 35.56 g of (+)-tartaric.acid and 1.3 g of NaHSO3 in 1 1 of deoxygenated water (WFI) The filter cake is added with stirring to this solution under N2. After the dobutamine free base has all dissolved, the solution is assayed for dobutamine by W and the volume of solution now containing the (+)-tartrate salt is adjusted by adding deoxygenated water (WFI) such that the final dobutamine concentration is 50 mg./ml. Specific rotation of the (+)-tartrate salt 25 [a] = +8.80. D Five milliliter aliquots are then transferred under N2 to a series of vials. The vials under N2 can be sealed as such or lyophilized and then sealed. Alternatively, dobutamine free base (the filter cake) can be stored as such and converted to the tartrate salt (or other salt) at a later time in a different area. In the above preparations, argon can be used in place of nitrogen. In addition, other antioxidants may be used in place of sodium sulfite or sodium bisulfite such as other alkali metal sulfites or bisulfites, thioglycerol, thioerithritol etc. Although (+)-tartaric and (-)tartaric acids were employed above, (i)-tartaric and mesotartaric acids are also fully operative and form dobutamine salts of high solubility. Furthermore, with any of the acids named, stereoisomers thereof can also be used rather than a racemate. Dobutamine content of all solutions is monitored with Uv. A typical injectable (i.v.) formulation using dobutamine tartrate has the following composition: 250 mg (base equivalent) dobutamine tartrate 4 mg sodium bisulfite water g.s. to 5 ml. Such solutions are placed in 5 ml glass ampoules and the ampoule sealed while maintaining an oxygen-free atmosphere. Glass vials with rubber stoppers can be used as well. The ampoules can be opened as needed to provide an i.v. injectable solution for treatment of cardiogenic shock. Alternatively, the solutions can be lyophilized and reconstituted with WFI prior to use. Formulations containing dobutamine salts prepared as above have superior stability characteristics. Accordingly, in one aspect of the invention there is provided a pharmaceutical formulation containing an aqueous solution of a dobutamine salt of an acid of formula I (preferably the (+)-tartrate) and an antioxidant (preferably sodium bisulphite).

Claims: CLAIMS 1. A salt of N-[3-(4-hydroxyphenyl)-l-methyl- propyl]-2-(3,4-dihydroxyphenyl)ethylamine with an acid of the formula I: (OH#1-8#C2-11 alkyl##COOH)1-2 2. Dobutamine tartrate. 3. Dobutamine (+)-tartrate. 4. Solid, crystalline, filterable dobutamine free base. 5. A pharmaceutical formulation comprising an aqueous solution of a dobutamine salt according to any one of claim 1 to 3, associated with an antioxidant. 6. A pharmaceutical formulation comprising an aqueous solution of dobutamine (+)-tartrate and sodium bisulphite. 7. A process for preparing a salt of dobutamine and an acid of formula: (OH#####C2-11 alkyl##COOH)1-2 I which comprises: (a) neutralizing dobutamine as the free base with the acid of formula (I), or (b) the metathetic reaction of an acid addition salt of dobutamine with a salt of the acid of formula (I). CLAIMS 1. A process for preparing a salt of dobutamine and an acid of formula: (OH#####C2-11 alkyl##COOH)1-2 I which comprises: (a) neutralizing dobutamine as the free base with the acid of formula (I), or (b) the metathetic reaction of an acid addition salt of dobutamine with a salt of the acid of formula (I). 2. A process according to claim 1, wherein the acid of formula (I) is tartaric acid. 3. A process according to claim 2, wherein the acid of formula (I) is (+)-tartaric acid.

Inventors: MASSEY, EDDIE HERMAN
Applicants: ELI LILLY AND COMPANY
Application year: 1985
Main classification: C07C215
IPC codes: A61K31, C07C51, C07C67, C07C59, C07C1, A61P9, C07C215, C07C213, A61K47