Studies On Probucol Self-Microemulsifying Drug Delivery System

Self-microemulsifying drug delivery system (SMEDDS) is a new-fashioned drug delivery system. It has many advantages such as absorbed rapidly, well stability, accuracy dosage, convenient administration, simple prepared, suitable for mass production. It is mainly used as vehicle for indissolvable drugs, to improve their dissolution and oral bioavailability. It has great prospect and application value.Probucol (PB) could be selected as the first drug for lipid-lowering, and it was used to cholesterol-lowering, anti-atherosclerosis, prevent restenosis after percutaneous transluminal coronary angioplas (PTCA), anti-oxygen and regression of xanthomas. Due to strong liposolubility, it could hardly dissolve in gastrointestinal fluids, which leads to the low oral bioavailability which is lower than 10% and large individual difference. Now, there is only probucol tablet on the market, which would influence the therapeutic efficacy and clinical application.Probucol self-microemulsifying drug delivery system (PB-SMEDDS) would be prepared, to improve its oral bioavailability and meet the requirement for clinical use.Part 1 Preformulation studyHPLC method of PB was developed for assay. The regression equation is A=3.0331×10⁴C+7.4002×10³(r=0.9999), which is linear over the range of 0.505～20.200μg·mL^-1. Its recovery, precision, stability all met the requirement of technology. Shake flask test was used to determine O/W apparent partition coefficients of PB in n-octanol/ 0.1mol·L-1HCl, n-octanol/ PBS (pH6.8) and n-octanol/water, the logarithm of which were 3.48, 3.64 and 3.42, respectively. The results indicated that PB was suitable for SMEDDS for its high liposolubility.Part 2 Prescription design and optimization of PB-SMEDDSThe balance solubility of PB in different excipients was assayed, selected the higher ones. According to the results, IPM was chose as the oil, Cremophor EL as the emulsifier, Labrasol as the co-emulsifier. Pseudo-ternary phase diagrams, oil (IPM)-mix emulsifier (Cremophor EL/Labrasol)-Water, were constructed by water-dropping method, to identify the efficient self-emulsification region, which was IPM (20%～40%) and mix-emulsifier (Km=3:1, 50%～80%). The prescription of PB-SMEDDS was optimized by multi-target orthogonal experiment, composed of IPM-Cremophor EL-Labrasol (30:52.5:17.5) and probucol 15%. Its particle size was (39.77±0.67) nm, PDI was (0.092±0.003) and particle size distribution was (14.44±0.13) nm, which all met the requirement of SMEDDS.Part 3 Pharmaceutics assessment for PB-SMEDDSThe pharmaceutics assessments for PB-SMEDDS were made. The self-emulsifying time of PB-SMEDDS was (52.33±0.47) s, which met the requirement of SMEDDS. Zeta potential of PB-SMEDDS and SMEDDS were both closed to 0, indicated that their stability mechanism maybe the steric hindrance of the interfacial film. HPLC method of PB-SMEDDS was developed for assay. The regression equation is A=2.9633×10⁴C+5.2608×10³(r=0.9999), which is linear over the range of 0.125～30.000μg·mL^-1. Its recovery, precision, stability all met the requirement of technology. With PB as the reference agent, direct dissolution test was used to evaluate the dissolution of drug from PB-SMEDDS. The results showed that the cumulated dissolution of PB-SMEDDS was up to 98.45% at 45min, which was 6.7 folds increase compared to PB. The release curves of PB-SMEDDS and PB fitted Hixson-Crowell equation most, indicated that the surface area was the main influence factor. Results of the stability experiments indicated that PB-SMEDDS could be kept stable under the low temperature tests (4℃), the ambient temperature tests (25℃) and the accelerated condition tests, indicated that it could be preservation in ambient temperature.Part 4 In situ intestinal absorption kinetics of PB-SMEDDS in ratHPLC method of PB-SMEDDS in circulation intestinal fluid was developed for assay. The regression equation is A=2.7106×104C+9.0976×103(r=0.9999), which is linear over the range of 0.502～30.120μg·mL^-1. Its recovery, precision, stability all met the requirement of technology. Used PB suspension as the reference agent, the absorption of PB-SMEDDS was researched in duodenum, jejunum, ileum, colon, using in situ intestinal absorption in rats, and the influences of this test were investigated. It was stable for PB-SMEDDS in circulation intestinal fluid, and it was almost no physical adsorption on the intestines'wall. There was no absorption saturation of PB-SMEDDS over the range of 50～150μg·mL^-1. Water absorption was almost the same at unit time in intestines. The results identified that PB-SMEDDS and PB suspension could be absorbed in the whole intestinal segments. The jejunum and ileum were the main absorption segments by passive diffusion with First-order kinetics. Compared to PB suspension, the absorption rate constants and average absorption percentage of PB-SMEDDS in the all intestinal segments were higher significantly (P<0.05). It can be seen SMEDDS could significantly increase the absorption in rats'intestine.Part 5 Investigation on bioavailability of PB-SMEDDS in ratHPLC method of PB in rats'plasma was developed for assay. The regression equation is A=7.23×10⁴C+1.6588×10⁴(r=0.9996), which is linear over the range of 0.1255～20.0800μg·mL^-1. It was accurate, reliable, specific and reproducible, met the requirement of technology. Used PB suspension as the reference agent, the study of pharmacokinetics on PB-SMEDDS in rats was carried out, and the obtained data were processed with 3P87. Plasma concentration-time profiles of PB-SMEDDS and PB suspension were both conformed to a two-compartment model (the coefficient weight is 1/C2). The tmax of PB-SMEDDS and PB suspension were 8.58h and 12.57h, respectively; Cmax were 6.72μg·mL^-1 and 0.34μg·mL^-1, respectively; AUC0-96h were 253.98μg·h·mL^-1 and 13.31μg·h·mL^-1, respectively. Compared with PB suspension, tmax of PB-SMEDDS in rat was shorted 3.99h, Cmax was increased 19.78 times, and AUC0-96h was increased 19.08 times. It was illustrated that PB-SMEDDS onset earlier, and it could improve the oral bioavailability of PB significantly.This study proved that PB was suitable for SMEDDS for its high liposolubility. Our group had prepared probucol self-microemulsifying drug delivery system (PB-SMEDDS) adopted self-microemulsifying technique. Pharmaceutics and biopharmaceutics assessments of PB-SMEDDS were made by 4 HPLC methods developed for assay. Its characters, such as self-emulsifying time, particle size and so on, all met the requirement of SMEDDS. The results presumed that its stability mechanism maybe the steric hindrance of the interfacial film. Its dissolution in vitro was 6.7 folds increase compared to PB. The absorption rate constants and average absorption percentage of PB-SMEDDS in the all intestinal segments were significantly higher than PB suspension, and the main absorption segments were jejunum and ileum by passive diffusion with First-order kinetics. Compared with PB suspension, tmax of PB-SMEDDS in rat was shorted 3.99h, Cmax was increased 19.78 times, and AUC0-96h was increased 19.08 times.The study was confirmed that PB-SMEDDS onset earlier, and it could improve oral bioavailability of PB significantly, which met the requirement for clinical use. The design, experiments and assessment in vivo and in vitro of PB-SMEDDS had never been reported.