doktorska disertacija
Tanja Rozman Peterka (Author), Uroš Urleb (Mentor)

Abstract

Slaba vodotopnost številnih novih učinkovin predstavlja visoko tveganje za neustrezno absopcijo po peroralni aplikaciji ter posledično nizko in variabilno biološko uporabnost. Z namenom izboljšanja biološke uporabnosti so raziskovalci razvili številne pristope za izboljšanje topnosti in hitrosti raztapljanja takšnih učinkovin. V doktorskem delu smo proučili kako amorfizacija, priprava trdnih disperzij in nanonizacija ter dejavniki okolja vplivajo na stabilnost učinkovine in farmacevtske oblike takrolimusa ter ovrednotili vpliv pomožnih snovi na stabilnost takrolimusa. Takrolimus je učinkovit imunosupresiv s kompleksno makrolidno strukturo. V vodi je praktično netopen (1 – 2 μg/mL). V svoji strukturi vsebuje 23-členski makrolidni lakton in izkazuje konformacijsko heterogenost v raztopinah ter je podvržen številnim kemijskim transformacijam. Za vrednotenje kemijske stabilnosti takrolimusa smo uporabili hitro in občutljivo UPLC metodo, ki omogoča učinkovito ločbo vseh ključnih znanih nečistot takrolimusa in njegovih ravnotežnih spojin. Dokazali smo, da je uporabljena metoda primerna za testiranje stabilnosti takrolimusa, saj poleg znanih nečistot dobro loči tudi številne neznane razkrojne produkte takrolimusa. V študiji prisilne razgradnje smo ugotovili, da je takrolimus v raztopini nestabilen v bazičnem, pri povišani temperaturi, svetlobi in ob prisotnosti radikalskega iniciatorja ter Fe3+ ionov. V raztopini je stabilen v blago kislih (pH 3 -5) do nevtralnih pogojih. Študije stresnega testiranja v trdnem in rezultati pospešene ter dolgoročne stabilnosti učinkovine so potrdili, da je amorfna oblika takrolimusa bistveno manj stabilna kot kristalni takrolimus monohidrat. Amorfna učinkovina je občutljiva na svetlobo, povišano temperaturo, vlago in oksidacijo pod vplivom kisika. Kristalni takrolimus monohidrat je stabilen na pogojih pospešene in dolgoročne stabilnosti, ni občutljiv na povišano temperaturo in vlago ter oksidacijo pod vplivom zračnega kisika. Kristalni takrolimus je občutljiv na svetlobo. S testiranjem kompatibilnosti in proučevanjem heterogenih farmacevstkih sistemov z amorfnimi trdnimi disperzijami smo ugotovili, da je amorfni takrolimus bolj podvržen interakcijam s pomožnimi snovmi kot kristalni takrolimus. Pod vplivom dejavnikov okolja in prisotnosti pomožnih snovi je takrolimus v amorfni obliki podvržen termično inducirani premestitvi, premestitvi ob prisotnosti Mg2+ ionov, reakcijam epimerizacije, dehidracije ter drugim kemijskim pretvorbam, ki so posledica radikalsko katalizirane avtoksidacije. Še posebej se je stabilnost amorfnega takrolimusa poslabšala ob prisotnosti magnezijevega stearata in stearinske kisline, medtem ko z hidroksipropilmetilcelulozo, natrijevim karmelozatom in laktozo nismo zaznali inkompatibilnosti. V prisotnosti magnezijevega stearata smo zaznali povečanje enega glavnega razkrojnega produkta, ki smo ga izolirali, določili njegovo strukturo in predlagali mehanizem nastanka. Ugotovili smo, da je v prisotnosti nekaterih di- in trivalentnih kovinskih kationov (Mg2+, Ca2+ in Fe3+) in bazičnega pH takrolimus podvržen reakciji premestitve v alfa-hidroksi kislino, ki poteče po principu benzilne premestitve. Ugotovili smo, da lahko na stabilnost amorfnega takrolimusa v heterogenih sistemih vplivamo z izbiro primernih pomožnih snovi, ustreznim pH mikrookolja ter zagotavljanjem suhih pogojev med izdelavo in shranjevanjem končne farmacevtske oblike. Z uporabljenimi pristopi izdelave amorfne učinkovine in pripravo amorfnih trdnih disperzij smo tudi uspešno povečali hitrost raztapljanja takrolimusa. Pri proučevanju stabilnosti farmacevstkega sistema z nanodelci oz. nanokristali takrolimusa smo ugotovili, da se je med mletjem ohranila kristalna oblika takrolimus monohidrata. Posledično so bili vzorci z nanosuspenzijo takrolimusa kemijsko bolj stabilni kot amorfna učinkovina in vzorci z amorfnimi trdnimi disperzijami. Z mletjem takrolimusa na krogličnem mlinu smo dosegli zmanjšanje velikost delcev na submikronski nivo in s tem povečali hitrost raztapljanja sicer slabo topnega takrolimusa.

Keywords

zdravilne učinkovine;slabo topne zdravilne učinkovine;hitrost raztapljanja;biološka uporabnost;trdne disperzije;imunosupresivi;takrolimus;farmacevtske oblike;pomožne snovi;amorfne oblike;kristalne oblike;nečistote;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UL FFA - Faculty of Pharmacy
Publisher: [T. Rozman Peterka]
UDC: 615.33.014.4(043.3)
COBISS: 300441344 Link will open in a new window
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Other data

Secondary language: English
Secondary title: Stability evaluation of poorly water-soluble macrolide drug in heterogeneous pharmaceutical systems
Secondary abstract: Poor water-solubility of many drug candidates represents high risk with regard to inadequate absorption and consequently poor and variable oral bioavailability of such drugs. A number of approaches have been developed to overcome poor oral bioavailability by enhancing solubility and dissolution rate of poorly soluble drugs. The aim of present work was to evaluate the influence of different solubility improvement technologies on stability of tacrolimus drug substance and its formulations. The effects of amorphization, solid dispersion preparation and nanosizing was studied. In addition, an influence of various environmental factors and effects of excipients on the stability behavior of tacrolimus was studied. Tacrolimus is a potent immunosuppressive drug. It is practically insoluble in water (1 – 2 μg/mL). Due to its complex structure based on 23-memberd macrolide lactone, tacrolimus exhibits different kinds of conformational heterogeneity in the solution and is subjected to various chemical transformations. In the present work, an advanced UPLC method for simultaneous separation of tacrolimus known impurities and its equilibrium compounds was applied for stability evaluation of tacrolimus. Stability indicating power of the method was confirmed by the appropriate separation of unknown tacrolimus degradation products formed in the forced degradation studies. Forced degradation study in solution proved tacrolimus instability under basic conditions, thermal stress, light and photolytic conditions and in the presence of radical initiator or metal ions. Tacrolimus was stable under neutral and acid conditions (pH 3-5). Solid-state degradation studies in addition to accelerated and long-term stability study confirmed that the amorphous form of tacrolimus is significantly less stable than crystalline tacrolimus monohydrate. Degradation studies conducted on amorphous drug substance revealed its sensitivity to light, elevated temperature, humidity and oxygen induced oxidation. Crystalline tacrolimus monohydrate was stable under conditions of accelerated and long-term stability, no degradation was observed at elevated temperature, high humidity or due to oxygen present in the air atmosphere. Crystalline tacrolimus was found to be sensitive to light. Solid-state excipient compatibility testing and stability evaluation of heterogeneous pharmaceutical systems containing amorphous solid dispersions revealed that amorphous tacrolimus is more susceptible to interactions with excipients than tacrolimus in crystalline form. Under the influence of environmental factors and in the presence of excipients, amorphous tacrolimus was subjected to thermal rearrangement, rearrangement due to presence of multivalent metal ions, epimerization, dehydration and other chemical transformations based on free radical catalyzed autoxidation. Significant degradation of amorphous tacrolimus was observed in the presence of magnesium stearate and stearic acid. On the other hand, hydroxypropyl methylcellulose, croscarmellose sodium and lactose were found to be compatible with amorphous tacrolimus. In the presence of magnesium stearate tacrolimus was decomposed toward a single degradation product. The impurity was isolated and its structure was elucidated. The impurity was found to be alpha-hydoxy acid, formed from the parent molecule through benzylic acid type rearrangement reaction in the presence of multivalent metallic ions under basic conditions. We have demonstrated that the stability of amorphous tacrolimus in heterogeneous systems can be improved by selection of suitable excipients, appropriate pH of the microenvironment and by applying dry storage conditions. Amorphous tacrolimus drug substance and formulations prepared as amorphous solid dispersions have also demonstrated an increased dissolution rate of tacrolimus. Stability evaluation of pharmaceutical system containing tacrolimus nanoparticles (nanocrystals) demonstrated enhanced chemical stability in comparison to amorphous tacrolimus and amorphous solid dispersions. During the milling process the crystalline form of tacrolimus monohydrate was retained. By wet ball milling approach a substantial reduction in particle size was achieved and consequently an increased dissolution rate of tacrolimus was observed.
Secondary keywords: Makrolidi;Disertacije;Topnost;Stabilnost;
Type (COBISS): Dissertation
Thesis comment: Univ. v Ljubljani, Fak. za farmacijo
Pages: VIII, 100 str.
ID: 15595307