Enhancement of naproxen solubility by addition of polymeric precipitation inhibitors to self(micro)emulsifying systems

Pri razvoju novih zdravilnih učinkovin (ZU) se pri večini kandidatov zanje srečamo s problemom slabe vodotopnosti. Z namenom izboljšanja njihove biološke uporabnosti (BU) lahko uporabimo naprednejše dostavne sisteme, kamor uvrščamo tudi samo(mikro)emulgirajoče (S(M)ES-e). Ti so izotropne zmesi lipidov, površinsko aktivnih snovi (PAS), hidrofilnih topil ali koemulgatorjev in ZU, ki ob stiku z vodnim medijem že ob rahlem mešanju (ali pri fizioloških pogojih in situ že pod vplivom peristaltike) hitro in spontano tvorijo (mikro)emulzije tipa olje-v-vodi. Njihova največja prednost je, da je ZU že raztopljena v emulzijskih kapljicah, s čimer obidemo fazo raztapljanja, ki je omejujoč faktor absorpcije. Je pa absorpcija omejena s prebavo lipidov, ki povzroči zmanjšanje solubilizacijske kapacitete – zaradi zmanjšanja topnosti pri tem nastane supernasičena raztopina, do katere privede tudi vgradnja večje količine ZU ali oddifundiranje hidrofilnih pomožnih snovi v vodni medij po disperziji. Supernasičenje teoretično olajša prehod skozi membrano gastrointestinalnega trakta (GIT), a učinkovina v taki raztopini teži k oboritvi že pred samo absorpcijo. Zato lahko S(M)ES-e izboljšamo z dodatkom polimernih zaviralcev obarjanja (angl. Polymeric Precipitation Inhibitors, PPIs), katerih naloga je ohranjanje učinkovine v metastabilnem supernasičenem stanju dovolj dolgo, da poteče absorpcija. Zaviranje obarjanja je lahko termodinamsko, kjer povečamo topnost ZU in zmanjšamo stopnjo supernasičenja, ali kinetično, kjer tvorba vezi poveča aktivacijsko energijo jedrenja in oteži nalaganje molekul ZU v kristalno rešetko. V obeh primerih zavremo obe stopnji obarjanja, tako jedrenje kot tudi rast kristala. Pri eksperimentalnem delu te naloge smo k sistemoma, izdelanima po dveh različnih recepturah in z že vgrajeno modelno učinkovino naproksenom, dodajali dva različna amfifilna polimera: poloksamer 407 in Soluplus®. Želeli smo ugotoviti, če uspešno zavreta obarjanje vgrajene ZU in torej res delujeta kot zaviralca obarjanja, na kakšen način to storita, ali po njunem dodatku v sistem še vedno nastane S(M)ES ter ali njun dodatek kako vpliva na kristalno strukturo naproksena. Na podlagi rezultatov lahko zaključimo, da dodatek obeh PPI-jev h klasičnim S(M)ES-om le-te izboljša, a se je Soluplus® pri tem izkazal kot neprimerljivo učinkovitejši od uporabljenega poloksamera. Z merjenjem velikosti kapljic in polidisperznega indeksa smo dokazali, da tudi ob njunem dodatku sistemi po disperziji tvorijo mikroemulzijo. Infrardeča spektroskopija je pokazala tvorbo vodikovih vezi med obema polimeroma in učinkovino in tako potrdila kinetično, povečevanje topnosti učinkovine v raztopinah z naraščajočo koncentracijo zaviralca pa termodinamsko zaviranje obarjanja. Z diferenčno dinamično kalorimetrijo pa smo še dokazali, da vgradnja v S(M)ES ter tudi dodatek polimera ne povzročita nikakršne kristalne modifikacije naproksena.When developing new drugs, candidates often show poor water solubility, resulting in low bioavailability. One approach to overcome this problem is their incorporation into advanced drug delivery systems, such as self(micro)emulsifying ones (S(M)ESs). Defined as isotropic mixtures of oils, surfactants, hydrophilic solvents or cosurfactants and drug, they rapidly form oil-in-water (micro)emulsion upon gentle agitation (that can be provided physiologically by the peristalsis) followed by dilution in an aqueous media. In those systems drug is already dissolved in emulsion droplets, so the dissolution, a limiting step in absorption, is avoided. But once they enter our body, lipids in S(M)ESs are subjected to digestion, which reduce solubilisation capacity so supersaturated solution is formed. It can also be result of greater amount of drug in the system or migration of hydrophilic excipients towards aqueous phase upon dispersion. Theoretically supersaturation causes enhanced flux across the intestinal wall, but a drug in supersaturated solution has the tendency to return to the equilibrium state (lowest chemical potential) by precipitation. That is why the inclusion of polymeric precipitation inhibitors (PPIs) can lead to improvement of conventional S(M)ESs. PPIs should maintain a metastable supersaturated state of an active pharmaceutical ingredient (API) in the GIT lumen for a time period sufficient for absorption. Inhibition effect may be achieved thermodynamically (by increasing solubility and therefore reducing degree of supersaturation) or kinetically (by forming bonds with drug). With any of those mechanisms both stages of precipitation, nucleation and crystal growth, are slowed down. In experiments performed for this thesis we were adding two amphiphilic polymers, poloxamer 407 and Soluplus®, to two differenty composed S(M)ESs already containing active ingredient naproxen. We wanted to find out if they are successful precipitation inhibitors, what is their mechanism of action, if the systems after their addition still form (micro)emulsions and if they somehow change crystal structure of incorporated drug. After our experimental work we can conclude that inclusion of both PPIs improved conventional S(M)ESs, but Soluplus® turned out to be much more effective than used poloxamer. With measurements of droplet size and polydispersity index we proved that even after the addition of chosen polymer our systems can still be classified as SMESs. We confirmed the formation of hydrogen bonds between inhibitors and naproxen and consequently their kinetic mechanism of action with infrared spectroscopy and after testing the solubility of API in solutions with increasing concentrations of PPIs we also proved their thermodynamic inhibition. Lastly, by using differential scanning calorimetry we showed that not incorporation into S(M)ES alone or even inclusion of PPI cause any crystal modification of naproxen