Phytantriol and glyceryl monooleate cubic liquid crystalline phases as sustained‐release oral drug delivery systems for poorly water soluble drugs I. Phase behaviour in physiologically‐relevant media

Objectives The potential utility of liquid crystalline lipid‐based formulations in oral drug delivery is expected to depend critically on their structure formation and stability in gastrointestinal fluids. The phase behaviour of lipid‐based liquid crystals formed by phytantriol and glyceryl monooleate, known to form a bicontinuous cubic phase in excess water, was therefore assessed in physiologically‐relevant simulated gastrointestinal media. Methods Fixed composition phase studies, crossed polarised light microscopy (CPLM) and small angle X‐ray scattering (SAXS) were used to determine the phase structures formed in phosphate‐buffered saline, simulated gastric and intestinal fluids in the presence of model poorly water soluble drugs cinnarizine, diazepam and vitamin E acetate. Key findings The phase behaviour of phytantriol in phosphate‐buffered saline was very similar to that in water. Increasing concentrations of bile components (bile salts and phospholipids) caused an increase in the lattice parameter of the cubic phase structure for both lipids. Incorporation of cinnarizine and diazepam did not influence the phase behaviour of the phytantriol‐ or glyceryl monooleate‐based systems at physiological temperatures; however, an inverse hexagonal phase formed on incorporation of vitamin E acetate. Conclusions Phytantriol and glyceryl monooleate have the potential to form stable cubic phase liquid crystalline delivery systems in the gastrointestinal tract. In‐vivo studies to assess their sustained‐release behaviour are warranted.     

脂质立方液晶纳米粒作为药物载体的研究进展

由两亲性脂质分散在水性环境中自发形成各种几何形态构成的药物输送载体正成为制剂载药系统研究的热点之一。脂质立方液晶纳米粒是一定浓度的两亲性脂质分散在水溶液中自组装成含双连续水区和脂质区的闭合脂质双层“蜂窝状(海绵状)”结构,该独特的内部双水道结构和巨大膜表面积使其能够包封各种不同极性和剂量的药物,具有多样化的药物包裹性。作为药物载体,脂质立方液晶纳米粒还具有载药量大、保护多肽蛋白类药物和制备工艺简单等优点;可口服、局部黏膜和注射等多种途径给药,在多种剂型中有广泛的应用。本文对脂质立方液晶纳米给药系统的研究进行归纳和总结,并展望了脂质立方液晶纳米粒新型药物载体的应用前景。     

Assessment of the in‐vivo drug release from pellets film‐coated with a dispersion of high amylose starch and ethylcellulose for potential colon delivery

Objectives The aim of this study was to test the ability of a colon targeting system comprising pellets film‐coated with a dispersion of high amylose starch (Hylon VII) and ethylcellulose (Surelease) (1 : 2 w/w) to deliver a model drug (5‐aminosalicylic acid; 5‐ASA) in vivo into the colon of rabbits. An uncoated pellet formulation was used as a control. Methods Six New Zealand female rabbits, approximately 2 kg, were randomly divided into two groups. Pellet formulations containing 50 mg/kg of 5‐ASA were filled into hard gelatin capsules size 4, and were administered orally using a cannula. The rabbits were fasted for 12 h before, and throughout, the study but had free access to water. Blood samples were collected, through a catheter inserted into the marginal vein of the ear, at pre‐determined times and the plasma analysed by a validated HPLC method with fluorescence detection. Results Analysis of the 5‐ASA plasma levels following administration of the uncoated pellets showed a C_max of 2.38 ± 0.49 μg/ml at 2 h post administration confirming that this system released the drug at an unspecific site, most likely in the rabbits' stomach and proximal small intestine. On the other hand, the coated formulation showed a delayed drug absorption (C_max 0.22 ± 0.19 μg/ml and t_max of 8 h), suggesting that the coating is able to prevent drug release in the stomach and small intestine, but allowing drug release in the colon. The coated pellets were retrieved from the rabbits' faeces after the 24‐h study. They had a drug content of < 40%, suggesting that the film‐coating had been digested by the bacterial amylases of the colon and the drug was released specifically in the colon of the rabbits. Conclusions Results from this study showed that the proposed drug delivery system has the potential to deliver drugs specifically into the colon.