Study On The Formulation Development Of Self-microemulsifying Drug Delivery System Of Nimodipine And Its In Vitro And In Vivo Evaluation

Objective: Nimodipine is one of dihydropyridines frequently used in clinic. Because of the poor water-solubility and obvious first pass effect, its bioavailability is only 4.8%～8.8%. Self-microemulsifying drug delivery system (SMEDDS) is a new preparation which could improve bioavailability and reduce adverse effect. SMEDDS could increase the dissolution of drug greatly and send the drug into blood by lymph circulation avoiding first pass effect. Based on the theory of SEDDS, we optimized the formulation of self-microemulsifying drug delivery system (SMEDDS) of nimodipine in order to improve the bioavailability and provide scientific basis for preparing SMEDDS of nimodipine.Methods: (1) The solubility of nimodipine in each adjuvant was tested firstly. Then the interaction between all the adjuvants and nimodipine was determined by differential scanning calorimetry (DSC). The designed and prepared 21 formulations of SEDDS were evaluated in vitro to optimize formulation according to the observation, emulsifying efficiency, particle diameter distribution, UV absorbance, dissolution and transmission electron microscope. In view of all the factors mentioned above, the optimized formulation was obtained. (2) After separated the whole intestine of rats, the intestine was affluxed with ice-cold physiological saline from the incision of intestine in order to clean the enteric cavity, and then affluxed with Krebs-Ringer solution saturated by mixed gas (95%O2,5%CO2)for one or two times. The intestine which was tied in one end was everted by a glass stick and filled with 2mL Krebs-Ringer solution from the other end that was tied later. The everted intestinal sac was put into a dissolution cup within 200mL Krebs-Ringer solution saturated by mixed gas (95%O2,5%CO2) and stired with the rotation rate of 50 r?min-1. SMEDDS contained 10, 20 or 40mg nimodipine and conventional tablet contained 20mg nimodipine were added at 0min respectively. After incubated for 30min, 60min, 90min, 120min or 240min, they were taken out, flushed with Krebs-Ringer solution for two or three times and weighed. 5mL physiological saline solution was added for every gram of intestine. Then the everted intestinal sac was homogenized by a homogenizer. The concentration of nimodipine in the homogenate was analyzed by HPLC. The superior, middle and inferior intestinal segments of approximately 10 cm in length were prepared just like the whole intestine we did before. The everted intestinal sac and SMEDDS contained 20mg nimodipine was added to the medium of 200mL Krebs-Ringer solution and incubated for 120min. By analyzing the concentration of nimodipine in the homogenate of intestine and the concentration of protein in the homogenate of intestine, we compared the absorption of nimodipine of SMEDDS and the conventional tablets in the whole intestine. In this way, the difference of absorption of nimodipine in the optimized formulation between different parts of intestine was studied. (3) The suspension of nimodipine conventional tablets and SMEDDS were orally administrated to two groups of rats with the dose of 12.5mg/kg respectively. The blood samples were drawn from the orbital vein of rats at 0,15,30,60,90,120,180,240,480,and 720min. As for the group of administrating by vein, the dose was 1.25mg/kg. The blood samples were also drawn from the orbital vein of rats at 0,5,10,20,40,60,120,180 , 240 , 480 and 720min. After dealing with all the samples, the concentration of nimodipine in the samples was analyzed by HPLC to get the concentration-time data. Then the main kinetic parameters were calculated by the DAS 2.1.1 software.Results:(1) The ratios(%) of nimodipine, ethyl oleate, Cremophor EL, and GMC in the optimized formulation were 3.5%, 40%, 40% and 16.5% respectively. The optimized formulation was able to emulsify rapidly under gentle agitation within 1min in the 0.1mol ?L-1 HCl. And the average droplet size was 58.6nm. The dissolution of the optimized formulation in the medium of 0.1mol ?L-1 HCl was 84.3% after 1 min. The optimized formulation could keep stable after three monthes in the lab environment protected from light. (2) The detecting method of nimodipine in the homogenate of rat intestine by HPLC was set up. The chromatographic column was C18 analytical column(250 x 4.6 mm, 5μm, phenomenex). The column temperature was maintained at 25℃. The mobile phase consisted of 70% acetonitrile and 30% water. The flow rate was 1mL? min-1 with detection wavelength at 350nm. Injection volume was 20μL. The regression equation of standard curve was: Y=5.9968X+0.0415,r=0.9995. The linear range was 0.02~1.0mg?L-1. By analyzing the concentration of nimodipine in the homogenate of intestine and the concentration of protein in the homogenate of intestine, we found that the concentration of homogenate of intestine was much higher in the three groups of SMEDDS than that of in the group of conventional tablets. And the three groups of SMEDDS were dose-dependent. The concentration kept balance until 60min. Nimodipine of SMEDDS could be absorbed in the entire intestine, however, the absorption decreased progressly from superior to inferior. When incubated in SMEDDS contained 20mg nimodipine, the content of nimodipine in every 100μg protein were 0.0281±0.0036μg , 0.0240±0.0031μg ,0.0218±0.0026μg for superior, middle and inferior intestine. (3) The detecting method of nimodipine in the plasma of rats by HPLC was set up. The chromatographic column was C18 analytical column(250 x 4.6 mm, 5μm, phenomenex). The column temperature was maintained at 25℃. The mobile phase consisted of 70% acetonitrile and 30% water. The flow rate was 1mL? min-1 with detection wavelength at 350nm. Injection volume was 20μL. The regression equation of standard curve was: Y=2.2872X+0.1645,r=0.9991,The linear range was 0.02~1.0mg?L-1. Main pharmacokinetics parameters of conventional tablets group and SMEDDS group were as following: Cmax were 0.101±0.018 mg?L-1 and 0.147±0.085 mg?L-1; AUC were 9.674±1.674mg·min·L-1 and 19.620±7.275mg·min·L-1; MRT were 71.784±2.739 min and 199.636±62.382 min, Tmax was almost the same. The absolute bioavailability of SMEDDS was 9.84%. Comparing with the conventional tablets, relative bioavailability of SMEDDS was 202.8%.Conclusion: (1) The optimized formulation is SMEDDS of nimodipine. (2)Both the results of everted intestinal sac in vitro and pharmacokinetics study in vivo of rats showed that the optimized formulation of SMEDDS could enhance the absorption of nimodipine which indicated that the optimized formulation of SMEDDS might have a promising future.