in describing embodiments of the present invention , specific terminology is employed for the sake of clarity . however , the invention is not intended to be limited to the specific terminology so selected . it is to be understood that each specific element includes all technical equivalents , which operate in a similar manner to accomplish a similar purpose . the above - described embodiments of the invention may be modified or varied , and elements added or omitted , without departing from the invention , as appreciated by those skilled , in the art in light of the above teachings . each reference cited herein is incorporated by reference as if each were individually incorporated by reference . the inventive solution has , as the active pharmaceutical agent , an antihistamine , evenly dissolved in a semi - solid aqueous vehicle . a preferred antihistamine is cetirizine . cetirizine , a piperazine derivative and carboxylated metabolite of hydroxyzine , is a potent histamine h 1 - receptor antagonist with antiallergic properties . cetirizine is used herein to describe not only the free compound of cetirizine , but also any pharmaceutically acceptable salt thereof . preferred are the acid addition salts , in particular , cetirizine dihydrochloride . the term cetirizine also includes racemic mixtures and the enantiomers of cetirizine . the solution provides a method of treating allergic conditions , such as allergic rhinitis and chronic uticaria in mammals . the methods include administering to a subject suffering from an allergic condition a storage stable pharmaceutical composition according to the invention . in one embodiment , the subject is a human . in another embodiment the allergic condition is allergic rhinitis or chronic idiopathic utircaria . the storage stable pharmaceutical composition can be administered to a patient in a dosage range of , for example , 0 . 5 mg to about 15 mg per day , preferably about 1 mg to about 12 mg per day , and more preferably 5 to 10 mg per day . the inventive solution comprises an aqueous and solution - stabilizing vehicle that is pharmaceutically acceptable . by a stabilizing solution , it is meant that not more than about 0 . 2 %, preferably not more than about 0 . 1 %, of the cetirizine is degraded into known or unknown impurities under varying temperature and humidity conditions . impurities are the unwanted chemicals that develop during formulation or upon aging of the formulated active pharmaceutical ingredient . an impurity can be any component present in the intermediate or active ingredient that is not the desired entity . an impurity may be a characterized or unknown chemical entity . the presence of these impurities , even in small amounts , may have an effect on the safety and efficacy of the pharmaceutical product . organic impurities may arise during the manufacturing process and / or storage of the drug substance . they may be identified or unidentified , volatile or non - volatile , and include starting materials , by - products of the synthesis procedure or degradation products . although the end products are washed with solvents , there is always the chance of having residual unreacted starting materials . impurities can also be formed by degradation of the end product during manufacturing of bulk drugs . in general , a pharmaceutical formulation may contain all of the above - mentioned types of organic impurities at levels varying from negligible to significant . there are several known impurities of cetirizine that are monitored during production of pharmaceutical formulations . 4 - chloro benzhydryl piperazine is a starting material in the manufacture of cetirizine active pharmaceutical ingredient . this compound is not a degradation product , and its impurity level in the formulation would depend on the amount that is in starting amount of cetirizine . cetamide ( 2 -[ 4 -( 4 - chloro - benzhydryl ]- 1 - piperazinyl )] ethoxy ) acetamide is an intermediate in the process of preparing the active pharmaceutical ingredient . thus , cetamide is a byproduct of the production steps and its impurity level in the formulation would also depend on the amount that is in the originally used cetirizine . glycerin - cetirizine esters are formed between the cetirizine carboxylic group and the hydroxyl groups of polyhydric alcohols over time . these esters are degradation products and have been previously described for the manufactured cetirizine oral solutions , and in u . s . pat . no . 6 , 171 , 618 . a hplc method was developed and validated for the determination of cetirizine dihydrochloride as well as its related impurities in the commercial oral solution and the inventive formulation . test samples of the cetirizine solutions were monitored for active and impurities . the testing was done at room temperature and at accelerated conditions of 30 ° c . and 40 ° c . cetirizine and its impurities were measured by hplc employing either agilent ( hewlett - packard ) 1100 hplc and / or waters alliance hplc system 2695 . chromatograms from the hplc show the peaks of detectable chemicals in the solution . the method was validated with respect to linearity and range , method accuracy , method precision , method specificity , limit of quantitation and method robustness . the validation method proved the hplc measurements to be accurate , precise , specific and robust . the measurement of impurities was made by measuring the relative retention time which is a ration of the retention time of the analyte to the retention time of the active , cetirizine . the guidelines for the international conference on harmonization ( ich ), require that , for a maximum daily dosage of 10 mg / day for children , any impurity greater than 0 . 5 % in a solution be qualified , any impurity in an amount of greater than 0 . 2 % be identified and any impurity greater than 0 . 1 % be reported . in general , liquid dosage forms are much more susceptible to both degradation and microbiological contamination . in this regard , water content , ph of the solution / suspension and the mutual interactions of ingredients are critical factors . the limit of detection is the minimum concentration (% w / w ) at which the analyte can reliably be detected . the limit of quantitation is the minimum concentration (% w / w ) at which the analyte can reliably be quantified . limits of detection and quantitation were determined by comparing measured signals from samples with known low concentrations of analyte to measured signals from blank samples . the storage stabilizing vehicle of the present invention comprises a thickener component and a carrier component , and may include organoleptic components . carbomers ( merck index 12 th ed ., no . 1878 ) can be used as thickeners in semi - solid pharmaceutical formulations ( see mehta et al ., u . s . pat . no . 6 , 071 , 523 ). carbomer 934p ( carbopol ® 974p ) is a suitable thickener or gelling agent . suitable concentrations from about 0 . 2 to about 1 . 0 %, and more specifically from about 0 . 40 to about 0 . 45 %, w / w . its rheology supports a high yield value ( handbook of pharmaceutical excipients third ed ., a . h . kibbe ( ed . ), pharmaceutical press , london , uk , 2000 , pg . 442 , 79 , 53 (“ handbook of pharm . excipients ”). carbomers are slightly acidic and must be neutralized e . g . with sodium hydroxide ( as needed to neutralize the carbomer up to about 0 . 08 % in particular formulations ) with a preferred ph range being about 6 . 2 to about 7 . 3 , providing the maximum viscosity plateau . the vehicle carrier component comprises propylene glycol up to about 20 %, or from about 3 to about 10 %. glycerin up to about 50 % may be present . additionally , sorbitol , up to 10 %, may be added as a vehicle and stabilizer . purified water comprises the bulk of the carrier component comprising from about 29 % to about 64 % of the formulation . the vehicle of the present invention has been described in u . s . publication no . 2005 - 0175642 a1 , herein incorporated by reference , as a stabilizing composition for a suspension of the piperidine antihistamine , loratadine . the solutions of the present invention may also contain edetate disodium ( edta ). edta is a chelating agent that forms a stable water - soluble complex with alkaline earth and heavy metal ions . it is useful as an antioxidant synergist , sequestering metal ions that might otherwise catalyze autoxidation reactions edta may also have synergistic effects as an antimicrobial when used in combination with other preservatives ( handbook of pharmaceutical excipients 4 th ed .). microbiological growth resulting from the growth of bacteria , fungi , and yeast in a humid and warm environment may result in oral liquid products that are unusable for human consumption . microbial contamination may occur during the shelf life and subsequent consumer - use of a multiple - dose product due to inappropriate use of certain preservatives in the preparations , or because of the semi - permeable nature of primary containers . the solution has antimicrobial activity . propylparaben ( up to about 0 . 04 %) and butylparaben ( 0 . 018 % to about 0 . 18 %) are suitable . other antimicrobial excipients may also be used . water activity is a measure of the free or unbound water in a product . water activity is a critical factor that determines shelf life . most bacteria will not grow at water activities below 0 . 80 , and most molds cease to grow at water activities below 0 . 70 . by measuring water activity , it is possible to predict which microorganisms will and will not be potential sources of spoilage . water activity determines the lower limit of available water for microbial growth . in addition to influencing microbial spoilage , water activity can have a major impact their color , taste , and aroma . water activity was measured using an awquick unit ( rotronic instrument corporation , huntington , n . y .). initially , the water activity was found to be too high and so sorbitol was introduced to decrease the water level . water activity measurements are shown in table v . the organoleptic ingredients improve the taste and appearance and do not negatively affect the solution , stability . the organoleptic agents in the following examples include coloring and flavoring agents , sweeteners and masking agents . the pharmaceutical formulation of the present invention may also contain additional active pharmaceutical ingredients , such as for example , decongestants , analgesics , antitussives and expectorants . any specific drug within these therapeutic classes is suitable for inclusion in the present invention . illustrative examples include analgesics such as aspirin , acetaminophen , naproxen , ketoprofen and ibuprofen ; decongestants such as pseudoepehedrine or phenylpropanolamine ; antitussives such as codeine , hydrocodone , or dextromethorphan ; and expectorants such as guaifenesin , including salts thereof . the storage stable solution was formulated to contain the following ingredients : as a comparative example , a cetirizine hydrochloride syrup ( 5 mg / 5 ml ) was prepared . the composition of the syrup is as follows : three exhibit batches of cetirizine spill resistant solution were manufactured with the formulation as given in example 1 . cetirizine solution sample 1 , sample 2 , and sample 3 were placed in amber bottles , and placed in an inverted position for a three - month time period for regulatory stability testing . the environmental conditions for the exhibit batches were either room temperature with average relative humidity ( rh ) ( 25 ± 2 ° c . ; 60 ± 5 % rh ), or high temperature with high relative humidity ( 40 ± 2 ° c . ; 75 ± 5 % rh ). total unidentified degradation products of the cetirizine stabilized solution were never above 0 . 1 %. in contrast , after three months of stability testing with the cetirizine syrup as prepared in example 2 , glycerin - cetirizine ester was the main degradation product . the total impurities seen in the cetirizine syrup formulations were ten times more than the total impurities seen in the stabilized solution . additionally , 0 . 6 % of the total impurities measured in the syrup were identified as glycerin - cetirizine ester . surprisingly , there was no detection of any glycerin - cetirizine ester in the stabilized solution . table iii total impurities cetirizine oral formulations ( hplc % total active ) temperature and relative humidity conditions 25 ± 2 ° c . ; 40 ± 2 ° c . ; sample 60 ± 5 % rh 75 ± 5 % rh cetirizine solution 0 . 07 % 0 . 06 % sample 1 cetirizine solution 0 . 09 % 0 . 08 % sample 2 cetirizine solution 0 . 09 % 0 . 07 % sample 3 cetirizine syrup 0 . 2 % 0 . 7 % ( 0 . 6 % identified as glycerin - cetirizine ester ) the impurities of the spill resistant stabilized cetirizine , as described in example 1 , was compared to a sample of the commercially available cetirizine syrup . both samples were placed in amber bottles , and placed in an inverted position for a three - month time period for regulatory stability testing . the environmental conditions for the exhibit batches were either room temperature with average relative humidity ( rh ) ( 25 ± 2 ° c . ; 60 ± 5 % rh ), or high temperature with high relative humidity ( 40 ± 2 ° c . ; 75 ± 5 % rh ). total unidentified degradation products of the cetirizine stabilized solution were never above 0 . 2 % for both room temperature and accelerated conditions . in contrast , after six months of stability testing with the commercial syrup impurity levels of 0 . 29 % at room temperature and 3 . 51 % at high temperature were recorded . 1 results shown are the average values from analysis of three lots . most bacteria will not grow at water activities below 0 . 91 , and most molds cease to grow at water activities below 0 . 80 . water activity was measured using an awquick unit ( rotronic instrument corporation , huntington , n . y .). water activity measurements are shown in table vii .
the present invention provides for a storage stable pharmaceutical liquid solution for oral administration having a pharmaceutically effective amount of an antihistamine and having a purity equal to or greater than about 99 % by weight - based hplc assay , residual solvents of less than about 0 . 5 %, and a total impurity of less than about 0 . 2 %. the storage stable solution preferably contains cetirizine . the present invention further provides a process of preparing the storage stable pharmaceutical liquid solution as well as a method of treating a mammal with a therapeutically effective amount of cetirizine in the stable pharmaceutical liquid solution .