Analysis of mycophenolic acid from saliva samples after its purification with the method of solidliquid extraction

Abstract

Pharmacological effect of a drug depends on its free fraction in plasma. By certain drugs, like immunosupresive mycophenolic acid, concentrations below therapeutic lead to rejection of the transplanted organ while concentrations above therapeutic lead to toxic effects, primarily on kidney and liver. For this reason constant monitoring of mycophenolic acid in plasma is necessary. Concerning frequency of sampling, availability and non-invasive way of sampling, saliva presents one of the best biological materials for analysis. On the other hand, numerous interfering endogen substances, impurities and high viscosity of saliva make this biological material difficult for purification. Mycophenolic acid has to be purified and concentrated from saliva to be consequently determined applying appropriate analytical method. In this paper solid phase extraction method for purification of saliva has been presented. The efficacy of solid phase extraction has been influenced by many different experimental parameters, so these parameters has to be strongly controlled, and protocol of extraction procedure has been proposed. In this way conditioning of polymeric sorbent has been done with methanol and purified water, samples have been applied together with 0.1 % formic acid, washing has been done with purified water and elution of mycophenolic acid has been performed with acetonitrile and 0.2% formic acid.

Farmakološki efekti leka direktno zavise od koncentracije leka u plazmi, odnosno njegove slobodne frakcije. Kod određenih lekova, kao što je imunosupresiv mikofenolna kiselina, smanjenje koncentracije dovodi do izostanka terapijskog efekta, dok povećanje koncentracije može dovesti do toksičnih efekata. Ozbiljni neželjeni efekti mogu dovesti do fatalnih ishoda, bilo da se radi o odbacivanju transplantiranog organa ili ozbiljnom oštećenju bubrega i jetre. Iz tog razloga potrebno je sprovoditi stalno praćenje nivoa mikofenolne kiseline u krvi. Imajući u vidu učestalost uzorkovanja, dostupnost i neinvazivan način sakupljanja, saliva ima prednost nad plazmom zbog čega se u skorije vreme sve više koristi kao uzorak. Međutim, zbog brojnih interferirajućih endogenih supstanci, nečistoća i viskoznosti, salivu je neophodno prethodno obraditi za kvalitativno i kvantitativno praćenje mikofenolne kiseline UPLC metodom. U ovom radu je opisana upotreba čvrsto-tečne ekstrakcije kao metode izbora za pripremu uzoraka salive. Pošto na efikasnost ekstrakcije utiču različiti eksperimentalni uslovi koje je potrebno strogo kontrolisati, predložen je protokol koji podrazumeva: kondicioniranje polimernog kertridža za čvrsto-tečnu ekstrakciju metanolom i vodom, nanošenje uzorka zajedno sa 0,1 % mravljom kiselinom, ispiranje kertridža vodom i eluiranje mikofenolne kiseline smešom acetonitrila i 0,2% mravlje kiseline.