aripiprazole has poor water solubility and thus is difficult to formulate as an aqueous injectable . in accordance with the present invention , it as been found that the water - solubility of aripiprazole may be sufficiently increased to allow it to be formulated as an aqueous injectable by complexing aripiprazole with a substituted - β - cyclodextrin . in effect , the cyclodextrin inhibits precipitation of the aripiprazole at the site of injection . the aqueous injectable formulation containing the complex of aripiprazole and the substituted - β - cyclodextrin may be administered preferably intramuscularly without causing unacceptable irritation at the muscular site . this is indeed surprising and unexpected since , as indicated above , a host of water - miscible co - solvent systems and water - immiscible co - solvent systems have been found to be unacceptable as carriers for injectable aripiprazole formulations because of the unacceptable irritation profile of such formulations . on the other hand , the aqueous injectable formulation of the invention delivers aripiprazole without causing unacceptable irritation at the site of injection . as will be seen hereinafter , the aripiprazole formulation in the form of an aqueous injectable will include an acid buffer and a base to adjust ph to desired levels . the substituted - β - cyclodextrin suitable for use herein refers to sulfobutyl ether β - cyclodextrin ( sbecd ) and hydroxypropyl - β - cyclodextrin ( hpbcd ), with sbecd being preferred . the term “ undue irritation ” or “ unacceptable irritation ” at the site of injection or at the muscular site refers to moderate to severe irritation which is unacceptable to the patient and thereby impacts unfavorably on patient compliance . the term “ reduced irritation ” at the site of injection or at the muscular site refers to generally minimal to mild irritation which is acceptable to the patient and does not impact unfavorably on patient compliance . the aripiprazole will form a complex with the substituted - β - cyclodextrin which complex may be dissolved in water to form an injectable formulation . however , physical mixtures of aripiprazole and the substituted - β - cyclodextrin are within the scope of the present invention as well . the complex or the physical mixture may also be compressed into a tablet or may be filled into capsules . the aripiprazole formulations of the invention may be formed of dry physical mixtures of aripiprazole and the substituted - β - cyclodextrin or dry inclusion complexes thereof which upon addition of water are reconstituted to form an aqueous injectable formulation . alternatively , the aqueous injectable formulation may be freeze dried and later reconstituted with water . thus , the inclusion complex in accordance with the invention , may be pre - formed , formed in situ or formed in vivo ( in the gastrointestional tract or the buccal cavity ). all of the above are contemplated by the present invention . the aripiprazole formulation of the invention in the form of an aqueous injectable will include an acid buffer to adjust ph of the aqueous injection within the range from about 3 . 5 to about 5 . examples of acid buffers suitable for use herein include acids such as hydrochloric acid , sulfuric acid , phosphoric acid , hydrobromic acid and the like , and organic acids such as oxalic acid , maleic acid , fumaric acid , lactic acid , malic acid , tartaric acid , citric acid , benzoic acid , acetic acid , methanesulfonic acid , toluenesulfonic acid , benzenesulfonic acid , ethanesulfonic acid and the like . acid salts of the above acids may be employed as well . preferred acids are tartaric acid , citric acid , and hydrochloric acid . most preferred is tartaric acid . the injectable formulation of the invention will have a ph within the range from about 3 . 5 to about 5 , preferably from about 4 to about 4 . 6 , and most preferably about 4 . 3 . in formulating the injectable , if necessary , the ph may be adjusted with a base such as an alkali metal hydroxide such as naoh , koh , or lioh , preferably naoh , or an alkaline earth metal hydroxide , such as mg ( oh ) 2 or ca ( oh ) 2 . in preparing the aqueous injectable formulation of the invention , the substituted - β - cyclodextrin will be employed in a weight ratio to the aripiprazole within the range from about 5 : 1 to 400 : 1 , preferably from about 10 : 1 to about 100 : 1 . each type of cyclodextrin employed requires a different ratio to inhibit or prevent precipitation of aripiprazole at the injection site . in preferred embodiments of the aqueous injectable of the invention , the substituted - β - cyclodextrin will be sbecd which will be employed in a weight ratio to aripiprazole within the range from about 5 : 1 to about 400 : 1 , preferably from about 20 : 1 to about 40 : 1 . the cyclodextrin may be present in an amount greater than that needed to complex the aripiprazole since the additional cyclodextrin could aid in dissolution of the aripiprazole . the aripiprazole will be present in the aqueous injectable formulation in an amount within the range from about 0 . 1 to about 2 . 5 % by weight , preferably from about 0 . 2 to about 1 . 5 % by weight based on the total injectable formulation . in preferred embodiments , the aripiprazole will be present in the aqueous injectable formulation to provide from about 1 to about 20 mg / ml of formulation , preferably from about 1 . 5 to about 8 mg / ml of formulation . in more preferred embodiments , the formulations of the invention will provide 2 mg aripiprazole / ml , 5 mg / ml and 7 . 5 mg / ml . fill volumes will preferably be 0 . 5 ml and 2 ml . ( 1 ) aripiprazole — in an amount to provide from about 1 . 5 to about 8 mg / ml of solution . ( 2 ) sbecd — in an amount from about 100 to about 200 mg / ml of solution . ( 3 ) acid buffer ( preferably tartaric acid )— in an amount from about 7 to about 9 mg / ml of solution to adjust ph from about 3 . 5 to about 5 . ( 4 ) base to adjust ph , preferably an alkali metal hydroxide , preferably naoh — in an amount to adjust ph from about 4 to 4 . 6 ( 5 ) water qs to 1 ml . the aripiprazole injectable formulation of the invention may be prepared as follows : tartaric acid or other acid buffer is dissolved in water for injection . the substituted - β - cyclodextrin ( preferably sbecd ) is dissolved in the acid buffer - water solution . aripiprazole is then dissolved in the solution . the ph of the solution is adjusted to within the range from about 3 . 5 to about 5 , preferably about 4 . 3 by adding base , such as sodium hydroxide or other alkali metal hydroxide or alkaline earth metal hydroxide . additional water for injection is added to obtain the desired batch volume . the resulting solution is aseptically filtered , for example , through a 0 . 22 % membrane filter and filled into vials . the vials are stopped and sealed and terminally sterilized . the aqueous injectable formulation of the invention will provide an amount of aripiprazole of at least 2 mg aripiprazole / ml , preferably at least 5 mg aripiprazole / ml , when the amount of aripiprazole provided by the complex is measured at a cyclodextrin concentration of 5 % w / v in water . the aripiprazole formulations of the invention are used to treat schizophrenia in human patients . the preferred dosage employed for the injectable formulations of the invention will be a 2 ml injection containing 7 . 5 mg aripiprazole / ml or a dose of 15 mg given three times daily at two hour intervals . the injectable formulation is preferably administered intramuscularly although subcutaneous and intravenous injections are effective as well . a clear colorless aripiprazole injectable solution ( 2 mg aripiprazole / ml , 4 mg / vial ) essentially free of particulate matter by visual inspection was prepared as follows . a stainless steel batching vessel was charged with an appropriate amount of water for injection usp . with continuous stirring , 78 g tartaric acid granular usp and 1500 g sulfobutyl ether β - cyclodextrin ( sbecd ) was added to the batching vessel and was dissolved in the water . aripiprazole 20 g was added to the batching vessel and stirring was continued until the aripiprazole was dissolved . sodium hydroxide 1n was added to the above solution to adjust the ph thereof to about 4 . 3 . additional water for injection usp was added to the above solution to adjust to the final batch size to 10 l with stirring . the above solution was aseptically filtered through a 0 . 22 μm membrane filter into a sterilized container 4 mg amounts of the above solution were aseptically filled into sterilized vials which were then aseptically stoppered with sterilized stoppers to seal the vials .
an aripiprazole formulation is provided which includes the antipsychotic agent aripiprazole in the form of an inclusion complex in a β - cyclodextrin , preferably , sulfobutyl ether β - cyclodextrin , which in the form of an injectable produces reversible generally minimal to mild irritation at the intramuscular injection site . a method for minimizing or reducing irritation caused by aripiprazole at an intramuscular injection site and a method for treating schizophrenia employing the above formulation are also provided .