Abstract:
A clear, stable solution of benzthiazide suitable for medical application has benzthiazide dissolved in an aqueous polyethylene glycol vehicle. The solution has a pH in the range of from about 3 to 6. The solution is prepared by mixing the benzthiazide in polyethylene glycol, stirring until the benzthiazide is dissolved, diluting with water, and adjusting the pH to between about 3 to 6. A benzyl alcohol preservative may be added if desired.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     Benzthiazide (3-[Benzylthio) Methyl]-6-Chloro-2H-1,2,4 -Benzothiadiazine-7-Sulfonamide 1,1-Dioxide) is known to be practically insoluble in water. The sodium or potassium salts of this compound are soluble but these aqueous solutions are not sufficiently stable at a pH suitable for the preparation of injections. At much higher pH these solutions are not suitable for intra-muscular injection because they often are accompanied by considerable necrotic reactions at the site of the injection. Previously, injectable benzthiazide was prepared for immediate use by the methods disclosed by U.S. Pat. Nos. 3,361,816 and 3,426,130 (incorporated by reference herein). Those methods use lyophylised unstable solutions which are reconstituted for immediate use. These methods have the disadvantage of requiring reconstitution, that is, they require additional time and care of the nurse, physician, veterinarian, etc. who administers the injection, or require the time of an assistant. Lyophylised solutions are not stable enough to be previously prepared and stored as solutions at room temperature. Typical shelf life of the prepared lyophylised solutions is two to three days under refrigeration, though in some instances life can be 30 to 90 days with refrigeration. 
     I have prepared stable solutions of benzthiazide which are suitable for parenteral administration of this therapeutically important diuretic, and can also be made suitable for other therapeutic methods of administration, such as syrups for peroral administration. The solutions are stable for up to three years or more at room temperature storage. The solutions eliminate the need for on the spot preparations and the time required thereby. The process for the preparation of a clear, stable aqueous solution of benzthiazide is conducted by dissolving the benzthiazide in an effective amount of a polyalkalene glycol and then diluting the solution with a suitable amount of water. Suitable preservatives, such as benzyl alcohol, may be added with the benzthiazide (or after) if multiple dosage containers are to be prepared and the pH of the solution is adjusted to between about 3 to 6 for injection. 
     Preferred polyalkalene glycols are the polyethylene glycols, particularly those having an average molecular weight of about 300. However, average molecular weights greater or less than 300 may be effectively used. Any polyalkalene glycol which will dissolve benzthiazide in an aqueous solution may be used. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention relates in particular to stable benzthiazide solutions suitable for intra-muscular or intravenous use and for peroral use. The solutions obtained by the application of the invention are extremely stable aqueous solutions. The solutions of the invention remain effective and are stable when stored for up to 2-3 years under normal room temperature conditions. Previous reconstituted lyophilized solutions are not adequate after 30-90 days under refrigerated storage at most. 
     By benzthiazide we mean (3-[Benzylthio) Methyl]-6-Chloro-2H-1,2,4-Benzothiadiazine-7-Sulfonamide 1,1-Dioxide) having the structural formula ##STR1## 
     In the solution of the invention typically there will be from about 1 to 5% benzthiazide and from about 45 to 85% polyalkalene glycol. From about 1 to 5% preservative will be used if multiple dosage units are prepared. The balance will be primarily water. 
     The solutions according to the invention are obtained by dissolving benzthiazide in an effective amount of a suitable polyalkalene glycol such as polyethylene glycol, or a mixture of polyalkalene glycol and water. The preservative is added, if required for multiple dose parenteral preparations, and the pH of the solution is adjusted to a value suitable for injection, e.g., between about 3 and 6 for injection with an effective organic or mineral acid. Suitable preservatives are, for example, benzyl alcohol, sodium formaldehyde sulfoxylate, and phenol. Suitable acids are, for example, hydrochloric acid, sulfuric acid, lactic acid and citric acid. 
     The following examples are illustrative of the practice of the invention. They are not to be deemed limitative in any respect and other expedients known to those skilled in the art may be employed. 
     EXAMPLE I 
     Ten grams of benzthiazide (3-[Benzylthio) Methyl]-6-Chloro-2H-1,2,4-Benzothiadiazine-7-Sulfonamide 1,1-Dioxide) (Pfizer, Inc. Fovane) are added with constant agitation to 450 grams of propylene glycol (average molecular weight 300,  Carbowax E300, Dow Chemical Company) and 10 grams of benzyl alcohol. The mixture is stirred constantly for five hours to obtain a clear solution. When all the benzthiazide is dissolved, 500 ml. of distilled water are added, the pH is adjusted to 5 with 2N. hydrochloric acid and the solution adjusted to 1 liter with distilled water for injection. This solution is rendered sterile by filtration and subsequently distributed into suitable injection bottles or ampoules. 
     EXAMPLE II 
     Twenty grams of benzyl alcohol and 20 grams of benzthiazide are added with constant agitation to 500 grams of polyethylene glycol. When all the benzthiazide is dissolved, 400 ml. of distilled water are added, the pH is adjusted to 4.5 with 85% lactic acid and the solution adjusted to 1 liter with distilled water for injection. This solution is rendered sterile by filtration and subsequently distributed into suitable injection bottles or ampoules. 
     EXAMPLE III 
     Thirty grams of benzthiazide and 30 grams of benzyl alcohol are added with constant agitation to 600 grams of propylene glycol. When all the benzthiazide is dissolved, 300 ml. of distilled water are added, the pH is adjusted to 4.5 with 5N. citric acid and the solution adjusted to 1 liter with distilled water for injection. This solution is rendered sterile by filtration and subsequently distributed into suitable injection bottles or ampoules for single dose use. 
     EXAMPLE IV 
     Forty grams of benzthiazide are added with constant agitation to 750 grams of propylene glycol. When all the benzthiazide is dissolved, 40 grams of benzyl alcohol and 150 ml. of distilled water are added and the pH is adjusted to 5.5 with 85% lactic acid and adjusted to 1 liter with distilled water for injection. This solution is rendered sterile by filtration and subsequently distributed into suitable injection bottles or ampoules. 
     EXAMPLE V 
     Fifty grams of benzyl alcohol and 50 grams of benzthiazide are added with constant agitation to 850 grams of propylene glycol. When all the benzthiazide is dissolved, 30 ml. of distilled water are added and the pH is adjusted to 5.5 with 2N. hydrochloric acid and adjusted to 1 liter with distilled water for injection. This solution is rendered sterile by filtration and subsequently distributed into suitable injection bottles or ampoules. 
     EXAMPLE VI 
     Ten grams of benzyl alcohol and 25 grams of benzthiazide are added with constant agitation to 650 grams of propylene glycol. When all the benzthiazide is dissolved, 250 ml. of distilled water are added and the pH is adjusted to 4.5 with 2N hydrochloric acid and adjusted to 1 liter with distilled water for injection. This solution is rendered sterile by filtration and subsequently distributed into suitable injection bottles or ampoules. 
     The solution of Example VI has been in room temperature storage test for over one year with no decline in potency and has been in an accelerated storage test for over 3000 hours. The accelerated storage test was conducted at 50° C. and is equivalent to three years normal storage. The results of the storage tests are given below. 
     
                       TABLE I______________________________________ROOM TEMPERATURE STORAGE     BENZTHIAZIDE    PERCENTAGE       ASSAY           OFMONTHS    mg./ml.         INITIAL ASSAY______________________________________0         28.8            100%3         28.9            100.3%6         29.3            101.7%9         29.2            101.3%12        29.1            101.0%______________________________________ 
    
     
                       TABLE II______________________________________ACCELERATED STORAGE     BENZTHIAZIDE    PERCENTAGE       ASSAY           OFHOURS     mg./ml.         INITIAL ASSAY______________________________________0         28.8            100% 500 hours     28.9            100.3%1000 hours     28.9            100%2000 hours     28.9            100.3%3000 hours     28.7             99.7%______________________________________ 
    
     The preceding specific embodiments are illustrative of the many experiments which have been conducted within the concepts of the invention. It is to be understood, however, that other expedients, known to those skilled in the art, can be employed or other specific conditions can be used, without departing from the spirit of the invention. 
     The stable, injectable solutions of benzthiazide disclosed herein are useful as diuretics, particularly for dogs and other small animals, as well as for other uses for which injectable benzethiazide is desired. Dosages for dogs of about 1 to 2 milligrams of benzythiazide per kilogram of body weight would normally be employed where an injectable diuretic was required, for example, where there was severe edema requiring an emergency use of a diuretic to reduce retained fluids. 
     The description herein is given by way of illustration and not for purposes of limitation. The scope of the invention is to be determined by the attached claims.