Studies On Liposomes Entrapping Cinnarizine Cyclodextrin Inclusion Complex

The concept of entrapping cyclodextrin-drug complexes into liposomes has been proposed by Me Cormack and Gregoriadis in 1994. This new concept combines the advantages of both CDs and liposomes into a single system by entrapping drug-cyclodextrin complex into liposomes and thus circumvents the problems associated with each system. CDs could accommodate water insoluble drugs to its hydrophobic inner cavity and thus form water soluble complex. However, on contact with the biological milieu（e.g., after intravenous injection）, cyclodextrin inclusion complexes can have their drug moiety displaced by other molecules with greater affinity for the cavity and be haemolytic or be removed rapidly from the blood circulation through the kidneys into the urine with ensuing toxicity. Although cyclodextrin can solve many problems in pharmaceutical preparation, the in vivo fate of cyclodextrin complex is far from satisfied. Liposomes entrap hydrophilic drugs in the aqueous phase and hydrophobic drugs in the lipid bilayers and transport drugs to their destination. Liposomes can be used to control the drug clearance rate in vivo and alter the tissue distribution. However, there are still many problems associated with liposome preparation, such as limited drug to lipid ratio, interference of some lipophilic drugs with bilayers, and these limits the range and amount of valuable drugs that can be associated with liposomes. Actually, only that the hydrophilic or lipophilic property of the drugs is extremely strong（logP＞4.5 or logP＜-0.3）can they be easily entrapped into liposomes. The drugs whose logP is between 1.70 and 4 tend to rapid leakage when entrapped into the liposomes. For drugs of this kind, we can attempt to prepare liposomes after entrap drugs to cyclodextins. The aim of present study was to combine the cyclodextrin and liposome into a single delivery system possessing the both advantages of the two and to increase drug loading capacity and change the in vivo pharmacokinetics of the cinnarizine complex.In our present study, cinnarizine was used as the hydrophobic drug model. The apparent partition coefficients and equilibrium solubility of cinnarizine in octanol/PBS with different pH were determined separately, and the degradation dynamics of cinnarizine at different pH was also investigated. Results show that the solubility was much higher and apparent partition coefficient was lower in acidic environment. The solubilizing effect of hydroxypropyl-β-cyclodextrin（HPCD）on cinnarizine was studied and the phase solubility diagram was depicted, suggesting a possibly of 1:2 interactions of cinnarizine and HPCD.The soybean phospholipids were used as materials to prepare liposomes. Thin-film dispersion method, ethanol injection method, and active loading method（pH gradient method）was attempted respectively to prepare cinnarizine liposomes. Results show that the entrapment efficiency was rather low, only approximately 10％. Then, cinnarizine HPCD complex was prepared by neutralization method and entrapped into liposomes. Entrapment efficiency was selected as index and the best formulation was obtained through orthogonal design. The optimal entrapment efficiency can reach 70％approximately. The method for entrapment efficiency determination was investigated including sephadex G-50 filtration chromatography, dialysis, ultracentrifugation at low temperature and minicolumn centrifugation method, and minicolumn centrifugation was selected eventually.In order to develop a preparation bearing long term storage, freeze-drying liposome were prepared and the protecting effect of different cryoprotectants and their combination on the appearance and reconstruction of freeze-drying liposome were evaluated. Results show that freeze-dried liposomes with good appearance and reconstruction can be attainted by using the combination of maltose-trehalose as cryoprotectants. The character of liposomes such as entrapment efficiency and particle size before and after freeze-drying didn’t change significantly.The qualities of the liposomes were evaluated, including the size distribution, particle morphology, zeta potential and in vitro release profile. Results exhibit that the particle size distribution was between 77-195 nm, the mean particle size was 128 nm, the liposomes were irregular spheres and the zeta potential was 25.5 mV. The release rate of the liposomes was slower than cyclodextrin complex in human plasma. Long term store stability of the liposomes before and after lyophilization was examined and compared with each other, including drug contents, the change of pH, the appearance, entrapment efficiency and particle size. Results show that the stability was obviously increased after lyophilization.The in vivo studies were carried out on wistar rats after intravenous administration of cinnarizine solution, cinnarizine cyclodextrin complex, liposomes entrapping cinnarizine-HPCD complex and F68 modified liposomes entrapping cyclodextrin complex. The blood samples were extracted and analyzed by HPLC using fluorescence detector. The pharmacokinetic parameters were calculated by statistical moment theory and analyzed by student’s t-test. Results show that the cyclodextrin liposomes display certain sustained release behavior and the in vivo fate of cyclodextrin complex was altered by entrapping into liposomes. The AUC and t_1／2 were all raised by encapsulating cyclodextrin into liposomes. Addition of long circulating material F68 didn’t change the pharmacokinetics of liposomes probably due to the low quantity applied.By entrapping cinnarizine cyclodextrin complex into liposomes, a novel drug delivery system was developed. The drug loading capacity was increased and the drug release profile was modified. The AUC was raised and t_1/2 was prolonged compared with drug solution and cyclodextrin complex after intravenous administration of drug to rats and the pharmacokinetics of cyclodextrin complex was modified. Combine the two drug delivery system into a single one may solve many problems associated with each system in pharmaceutical preparation. The present study developed a new kind of liposomes encapsulating cyclodextrin inclusion complex by using cinnarizine as model drug, and provide a reference for the research of liposomes entrapping cyclodextrin complex.