in the following detailed description of the preferred embodiments , reference is made to the accompanying drawings , which form a part thereof , and within which are shown by way of illustration specific embodiments by which the invention may be practiced . it is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention . the present invention is directed to a method of treating of neuropsychiatric diseases using lithium salicylate . lithium salicylate was recently unexplored and research has shown that this lithium salt exhibits profoundly different pharmacokinetics compared to the more common fda approved salt , lithium carbonate , in rats . remarkably , lithium salicylate produced elevated plasma and brain levels of lithium beyond 48 hours post - dose without the sharp peak that contributes to the toxicity problems of current lithium therapeutics . male sprague dawley rats weighing 200 - 250 grams were dosed via oral gavage with 4 meq . kg − 1 elemental lithium as lithium salicylate dissolved in deionized water ( n = 3 per time point per lithium salt ). blood and brain were collected and lithium was measured using atomic absorption spectroscopy ( aas ). plasma and brain lithium measurements are plotted as mean ± sem in fig1 a and 1b , respectively . lithium salicylate produced elevated lithium plasma levels through the first 48 hours and was eliminated slowly . interestingly , the lithium salicylate formulation produced elevated brain levels only at 24 and 48 hours post - dose . table 1 shows some pertinent pharmacokinetic parameters in the experiment . however , these estimates should be used as preliminary indicators since only four carefully selected time points were utilized to limit the use of animals as much as possible . due to the utilization of the same experimental protocol and time points for the pharmacokinetics study as previously used by smith et al . for lithium carbonate ,[ 7 ] the determination of the relative bioavailability ( f rel ) of lithium salicylate compared to lithium carbonate ( table 1 ) was possible . the relative bioavailability of lithium salicylate was lower than lithium carbonate . the plasma and brain f rel of lithium salicylate was 0 . 35 and 0 . 54 , respectively . there is a large disparity in regards to comparative studies of the pharmacokinetics of lithium salts in the peer - reviewed literature . until now , only lithium chloride , carbonate , and orotate have been subjected to these types of studies [ 16 ]. the present study represents the first in vivo pharmacokinetic assessment of lithium salicylate . because lithium salicylate is considered pharmaceutically acceptable and amenable for cocrystallization using crystal engineering techniques [ 7 ], such pharmacokinetic data will be critical in advancing lithium therapeutics . interestingly , lithium salicylate exhibited an unexpected pharmacokinetic profile that is unlike any other lithium salt reported in the literature to date . the known toxicity issues of fda approved lithium salts could be exacerbated by their pharmacokinetics given its narrow therapeutic window . as previously reported , lithium carbonate peaks rapidly and is eliminated within 48 hours [ 7 ]. comparatively , the lithium salt in the present study underperformed lithium carbonate from bioavailability standpoints . however , given that oral bioavailability is not a problem with lithium therapeutics [ 17 , 18 ] it is not anticipated that this discrepancy will disqualify either of these salts for development as drugs . in fact , the plateau plasma levels observed in this study of lithium salicylate could improve the safety of lithium therapy and , consequently , improve patient compliance . this is supported by previous investigators who suggested that an ideal lithium preparation would attenuate high blood level peaks and exhibit gradually declining blood concentrations [ 19 ]. encouragingly , this is precisely the pharmacokinetic profile that was produced by lithium salicylate in the study ( see fig1 a and 1b ). previous attempts at formulating proprietary controlled release lithium therapeutics have been somewhat successful at prolonging lithium plasma levels [ 20 ]. nonetheless , the lithium salicylate formulation still produced the initial plasma spike attributable to toxicity problems observed in lithium therapy . it was also discovered that lithium salicylate produced comparatively lower plasma lithium exposure than other lithium salts ( e . g . lithium lactate ), but lithium salicylate produced better brain exposure . thus , biodistribution also appears to be affected by the choice of anion . indeed , these pharmacokinetic differences were unexpected since lithium salicylate was administered fully dissolved in an aqueous solution , eliminating the possibility of solubility - mediated effects . this would lead one to predict that the lithium pharmacokinetics would be similar for lithium salicylate and other lithium salts ( e . g . lithium lactate ). since that was not the case , it is hypothesized that the observed “ plateau effect ” and modulated brain biodistribution of lithium as lithium salicylate is likely due to absorption , distribution , metabolism , and / or elimination ( adme ) effects from the salicylate anion . the precise mechanism for this is unclear . however , this could be due to the chemical modification of the physiological transporter ( s ) of lithium ions in vivo . for example , sodium ion transporters have similar permeability for both sodium and lithium ions [ 21 ]. it is feasible that salicylate chemically modifies the sodium ion transporter , changing its permeability . because lithium is so effective at treating neuropsychiatric diseases such as bipolar disorder and suicidality [ 1 , 22 , 23 ] it is still used despite known toxicity issues that require frequent blood monitoring by a clinician . finding a new molecule that is a true “ lithium mimetic ” is probably a lost cause and recognize that crystal engineering approaches like cocrystallization could solve the toxicity issues . the preliminary data presented here demonstrates that some currently available but understudied lithium salts ( e . g . lithium salicylate ) may also solve the toxicity issues of conventional lithium salts ( e . g . lithium carbonate and lithium citrate ). however , developing new lithium salts as drugs would require significant investment from a pharmaceutical company without composition of matter patent protection . cocrystals are patentable [ 24 ], which improves the likelihood of realizing a good return on the investment required to develop them as a new drug . moreover , cocrystals of lithium salts might also offer improved efficacy since the coformers can be rationally selected to be synergistic as discussed in recent crystal engineering efforts [ 13 , 14 ]. reagents and materials . lithium salicylate (≧ 98 % purity ) was purchased from sigma - aldrich corporation ( st . louis , mo ., usa ) and used as such without further purification . the chemical structure of lithium salicylate is shown in fig2 . lithium salicylate was characterized using powder x - ray diffraction . this data is included as esi . pharmacokinetics studies . previously described methodologies were used for the pharmacokinetics studies [ 7 ]. male sprague dawley rats weighing 200 - 250 grams were purchased from harlan ( harlan sprague dawley inc ., indianapolis , ind .). the animals were housed at the moffitt cancer center vivarium ( tampa , fla .) with a 12 - hour light - dark cycle . the rats were allowed to acclimate for a period of one week before any experiments are carried out . all experiments were conducted in accordance with usf iacuc approved protocols . they were allowed free access to food and water throughout the experiment . the rats were dosed via oral gavage with 4 meq . kg − 1 elemental lithium as lithium salicylate dissolved in deionized water . animals in each treatment group were euthanized at 2 , 24 , 48 , and 72 hours ( n = 3 per time point per lithium salt ) and blood was collected by cardiac puncture and carefully perfused with a pressure controlled pump to maintain microvasculature integrity before removing brain tissue . blood was centrifuged at 1600 × g at room temperature for 10 minutes and plasma was separated . a 500 ml aliquot was diluted 10 fold in a 5 % tca and 10 % isopropyl alcohol ( ipa ) solution , vortexed and allowed to sit for 10 minutes in order to precipitate proteins . these aliquots were centrifuged at 3000 × g for 30 minutes and the supernatant was transferred to clean tubes prior to measuring lithium content using atomic absorption spectroscopy ( aas ). brains were rinsed with pbs , weighed , and an equal volume of concentrated hno3 was added . the brains were heated in this nitric acid solution for 1 hour , allowed to cool to room temperature , then centrifuged at 3000 × g for 1 hour . the supernatant was removed and diluted 10 fold in 10 % ipa prior to measuring lithium content using aas ( shimadzu aa - 6200 ). peak height measurements were carried out referring to values obtained for standards of known concentrations . lithium measurements were plotted using graphpad prism software ( graphpad software , inc .) as mean ± sem in fig1 . two tailed t - tests were used to assess the statistical significance at each time point for the pharmacokinetic curves . the criterion for rejection of the null hypothesis was p & lt ; 0 . 05 . phoenix winnonlin ® version 6 . 3 ( pharsight corporation , mountain view , calif .) was used to conduct a non - compartmental analysis of the pharmacokinetic data and generate the pharmacokinetic parameters in table 1 as mean ± sem . the reported parameters include c max , t max , area under curve ( auc ), and relative bioavailability ( f rel ). 1 . k . thies - flechtner , b . muller - oerlinghausen , w . seibert , a . walther and w . greil , pharmacopsychiatry , 1996 , 29 , 103 - 107 . 2 . f . k . goodwin , b . fireman , g . e . simon , e . m . hunkeler , j . lee and d . revicki , jama , j . am . med . assoc ., 2003 , 290 , 1467 - 1473 . 3 . a . cipriani , k . hawton , s . stockton and j . r . geddes , bmj [ br . med . j . ], 2013 , 346 , f3646 . 4 . t . fukumoto , s . morinobu , y . okamoto , a . kagaya and s . yamawaki , psychopharmacology , 2001 , 158 , 100 - 106 . 5 . t . leyhe , g . w . eschweiler , e . stransky , t . gasser , p . annas , h . basun and c . laske , j . alzheimer &# 39 ; s dis ., 2009 , 16 , 649 - 656 . 6 . c . j . yuskaitis and r . s . jope , cell . signalling , 2009 , 21 , 264 - 273 . 7 . a . j . smith , s . h . kim , n . k . duggirala , j . jin , l . wojtas , j . ehrhart , b . giunta , j . tan , m . j . zaworotko and r . d . shytle , mol . pharm ., 2013 , 10 , 4728 - 4738 . 8 . p . s . klein and d . a . melton , proc . natl . acad . sci . u . s . a ., 1996 , 93 , 8455 - 8459 . 9 . j . h . allison and m . a . stewart , nature new biol ., 1971 , 233 , 267 - 268 . 10 . s . j . pollack , j . r . atack , m . r . knowles , g . mcallister , c . i . ragan , r . baker , s . r . fletcher , l . l . iversen and h . b . broughton , proc . natl . acad . sci . u . s . a ., 1994 , 91 , 5766 - 5770 . 11 . n . singh , a . c . halliday , j . m . thomas , o . v . kuznetsova , r . baldwin , e . c . woon , p . k . aley , i . antoniadou , t . sharp , s . r . vasudevan and g . c . churchill , nat . commun ., 2013 , 4 , 1332 . 12 . t . d . gould and h . k . manji , neuropsychopharmacology , 2005 , 30 , 1223 - 1237 . 13 . d . braga , f . grepioni , l . maini , d . capucci , s . nanna , j . wouters , l . aerts and l . quere , chem . commun ., 2012 , 48 , 8219 - 8221 . 14 . j . wouters , f . grepioni , d . braga , r . m . kaminski , s . rome , l . aerts and l . quere , crystengcomm , 2013 , 15 , 8898 - 8902 . 15 . u . s . food and drug administration , guidance for industry : regulatory classification of pharmaceutical co - crystals , center for drug evaluation and research , silver spring , u . s ., april 2013 . 17 . u . groth , w . prellwitz and e . jahnchen , clin . pharmacol . ther ., 1974 , 16 , 490 - 498 . 18 . e . m . trautner , r . morris , c . h . noack and s . gershon , med . j . aust ., 1955 , 42 , 280 - 291 . 19 . s . lippmann and r . evans , hospital and community psychiatry , 1983 , 34 , 113 - 114 . 20 . j . emami , n . tavakoli and a . movahedian , j . pharm . pharm . sci ., 2004 , 7 , 338 - 344 . 22 . r . j . baldessarini , l . tondo and j . hennen , ann . n . y . acad . sci ., 2001 , 932 , 24 - 38 ; discussion 39 - 43 . 23 . f . k . goodwin , b . fireman , g . e . simon , e . m . hunkeler , j . lee and d . revicki , jama , j . am . med . assoc ., 2003 , 290 , 1467 - 1473 . 24 . o . almarsson , m . l . peterson and m . zaworotko , pharm . pat . anal ., 2012 , 1 , 313 - 327 . 25 . adam j . smith , seol - hee kim , jun tan , kevin b . sneed , paul r . sanberg , cesar v . borlongan , and r . douglas shytle , rsc adv ., 2014 , 4 , 12362 . the advantages set forth above , and those made apparent from the foregoing description , are efficiently attained . since certain changes may be made in the above construction without departing from the scope of the invention , it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense . it is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described , and all statements of the scope of the invention that , as a matter of language , might be said to fall therebetween .
despite its narrow therapeutic window , lithium is regarded as the gold standard comparator and benchmark treatment for mania . attempts to find new drugs with similar therapeutic activities have yielded new chemical entities . however , these new drugs have yet to match the many bioactivities attributable to lithium &# 39 ; s efficacy for the treatment of neuropsychiatric diseases . consequently , an intense effort for re - engineering lithium therapeutics using crystal engineering is underway . the evaluation of pharmacokinetics of previously unexplored lithium salts with organic anions has found that these lithium salts exhibit profoundly different pharmacokinetics compared to the more common fda approved salt , lithium carbonate , in rats . remarkably , lithium salicylate produced elevated blood and brain levels of lithium beyond 48 hours post - dose without the sharp peak that contributes to the toxicity problems of current lithium therapeutics .