Formulation and evaluation of cyclodextrin-based drug delivery system for oral application of zaleplon

Nesanica je jedan od najčešćih poremećaja spavanja koji zahvaća oko 30% odrasle populacije, a značajno je češći kod starije populacije i psihičkih bolesnika. Zahvaljujući svojim farmakološkim svojstvima, zaleplon je hipnotik izbora za kratkotrajno liječenje nesanice. Međutim, slaba topljivost i razgradnja u jetri ograničavaju mu oralnu bioraspoloživost na samo 30%. Stoga je cilj ovog rada pripremom inkluzijskih kompleksa s ciklodekstrinima poboljšati topljivost lijeka u vodi, a uklapanjem u oblik s kontroliranim oslobađanjem razviti novi terapijski sustav koji bi mogao značajno unaprijediti terapijsku učinkovitost ovog lijeka. Spektrofluorimetrijska i solubilizacijska ispitivanja su pokazala da β-ciklodekstrin sa zaleplonom stvara komplekse prikladne stabilnosti, no topljivost nastalog kompleksa je ograničena. Od kemijski modificiranih derivata, nasumično metilirani β-ciklodekstrin se pokazao najprikladnijim, dok je topljivost i stabilnost inkluzijskih kompleksa zaleplona sa sulfobutil-β-ciklodekstrinom i hidroksipropil-β-ciklodekstrinom nešto niža. Nastajanje inkuzijskih kompleksa s navedenim derivatima ciklodekstrina je potvrđeno primjenom 1H NMR spektroskopije, a određena je i njihova struktura. Sustav karakterizira istovremeno prisustvo dva načina vezanja. Prvi, dominantni način uključuje inkluziju fenilnog prstena molekule zaleplona u centralnu šupljinu molekule ciklodekstrina, a drugi inkluziju pirazolo[1,5-a] pirimidinskog prstena molekule lijeka, dok je nastajanje kompleksa višeg reda isključeno. Termodinamička ispitivanja su pokazala da je nastajanje kompleksa zaleplona s β-ciklodekstrinom i njegovim metiliranim i hidroksipropiliranim derivatima entalpijom uvjetovani proces, dok je kompleksiranje lijeka sa sulfobutil- β-ciklodekstrinom entropijom vođen proces. U oba slučaja riječ je o spontanom procesu. Dodatkom hipromeloze je značajno povećan solubilizacijski potencijal metiliranog β-ciklodekstrina uslijed nastajanja ternarnih kompleksa lijek-ciklodekstrin-polimer, dok hidrofilni polimeri nisu utjecali na topljivost i stabilnost kompleksa zaleplona s β-ciklodekstrinom. Binarni i ternarni kompleksi zaleplona s navedenim ciklodekstrinima i hidrofilnim polimerima u čvrstom stanju pripremljeni su tehnikom sušenja raspršivanjem. Diferencijalna pretražna kalorimetrija, difrakcija rentgenskih zraka na prašku te pretražna elektronska mikroskopija su pokazale djelomičnu amorfizaciju lijeka u binarnim i ternarnim kompleksima s β-ciklodekstrinom, dok su kompleksi s metiliranim-β-ciklodekstrinom bili u potpunosti amorfne strukture. Binarni kompleksi s metiliranim-β- ciklodekstrinom te ternarni kompleksi s metiliranim-β-ciklodekstrinom i hipromelozom bili su najučinkovitiji u povećanju topljivosti zaleplona u odnosu na ostale komplekse. Korištenjem manitola kao topljivog punila te ternarnog kompleksa zaleplona s metiliranim β-ciklodekstrinom i hipromelozom pripremljene su tablete koje omogućuju oslobađanje doze lijeka u samo 5 minuta, osiguravajući brz početak djelovanja lijeka. Topljivi kompleksi zaleplona s u vodi topljivim, polimernim derivatom ciklodekstrina su pripremljeni i tehnikom mljevenja u vibracijskim mikromlinovima. Nakon 90 minuta mljevenja pri frekvenciji od 24 Hz dobiven je amorfni produkt koji otapanjem u vodi prelazi u inkluzijski kompleks, što je dokazano 1H-NMR spektroskopijom. Primjenom tehnike sušenja raspršivanjem pripremljene su mikrosfere s pH ovisnim oslobađanjem zaleplona kao novi terapijski sustav za liječenje nesanice koju karakterizira prerano buđenje te nemogućnost naknadnog usnivanja. Matriks koji sadrži 80% Eudragita S100 i 20% glicerolmonostearata pokazao se optimalnim u sprječavanju neželjenog oslobađanja lijeka pri nižim pH-vrijednostima medija, dok je uklapanjem 50% doze lijeka u obliku inkluzijskog kompleksa s metiliranim β-ciklodekstrinom osigurano potpuno oslobađanje lijeka u umjetnom crijevnom mediju, kinetikom nultog reda (k0=155 μg/min).Insomnia is one of the most common sleep disorders affecting about 30% of adult population, while its prevalence is even higher among elderly and psychiatric patients. Pharmacological properties makes zaleplon the drug of choice for the short term treatment of insomnia, but its low aqueous solubility and intensive metabolism in liver are reducing its oral bioavailability to only 30%. Therefore, the aim of this work was to improve aqueous solubility of zaleplon through inclusion complexation and to develop a novel drug delivery system able to enhance its therapeutical efficiency. Spectrofluorimetric and phase solubility studies showed that parent β-cyclodextrin forms stable inclusion complexes with zaleplon, but aqueous solubility of the complexes formed was limited. Among chemically modified β- cyclodextrin derivatives, randomly methylated derivative was the most efficient, while the solubility and stability of zaleplon complexes with sulphobutyl- and hydroxypropyl-β-cyclodextrin was less pronounced. The inclusion complex formation in all cases was confirmed by 1H-NMR spectroscopy. The structure of the complexes formed was characterised by the presence of two different binding modes which existed simultaneously in the solution. The first and the dominant one occurs through inclusion of phenyl moiety of the drug into central cavity of cyclodextrin molecule, while the other involves the inclusion of the pyrazolo[1,5-a]pyrimidine ring of the drug. The formation of higher order complexes was not demonstrated. Thermodynamic studies showed that complexation of zaleplon with β- cyclodextrin and its randomly methylated and hydroxypropylated derivatives was enthalpy driven, while entropy driven complexation was observed in case of sulphobutyl-β-cyclodextrin. In all cases, inclusion complex formation was a spontaneous process. Addition of hypromellose enhanced significantly the solubilising and complexing potential of randomly methylated β-cyclodextrin due to ternary complex formation, while hydrophilic polymers had no effect on solubility and stability of zaleplon complexes with parent β-cyclodextrin. Binary and ternary zaleplon complexes with cyclodextrins and polymers tested were prepared by spray-drying. Differential scanning calorimetry, X-ray powder diffractometry and scanning electron microscopy showed only partial drug amorphization of the drug in binary and ternary complexes with β-cyclodextrin, while all complexes with randomly methylated β-cyclodextrin were completely amorphous. The inclusion complex formation in spray-dried products was confirmed by the solid state NMR. Binary and ternary complexes with randomly methylated β-cyclodextrin and hypromellose were the most efficient in increasing the dissolution rate of zaleplon. The use of mannitol as a soluble filler and ternary inclusion complex with randomly methylated β-cyclodextrin and hypromellose allowed formulation of tablets which released the complete drug dose in 5 minutes, providing fast onset of drug action. Highly soluble zaleplon complexes with soluble, polymeric β-cyclodextrin derivative were also prepared by co-grinding in high energy vibrational micromill. Co-grinding at frequency of 24 Hz resulted in an amorphous product which is readily soluble in water, forming inclusion complexes as demonstrated by 1H-NMR spectroscopy. Spray-drying technique was used to prepare pH-responsive zaleplon microspheres with delayed release properties as a novel drug delivery system for treatment of specific type of insomnia characterised with premature awaking and inability to fall asleep again. Matrix containing 80% of Eudragit S100 and 20% of glycerol monostearate was demonstrated to be optimal, preventing the drug release at high pH-values. The incorporation of 50% of the drug dose in form of binary inclusion complex with randomly methylated β-cyclodextrin ensured complete drug release in simulated intestinal media, with the zero-order release rate (k0=155 μg/min)