Biol. Pharm. Bull. 30(10) 1918—1922 (2007)

shen) listed in the Chinese Pharmacopoeia (CP) is widely used traditional Chinese medicine to treat coronary heart disease, cerebrovascular disease, hepatocirrhosis and against bacteria. The chemical constituents of Salvia miltiorrhiza have been studied extensively and well documented. More than 30 diterpenoid quinone pigments, particularly known as tanshinones have been isolated and identified from Danshen. Tanshinone I, tanshinone IIA, and cryptotanshinone are the main abietane-type diterpense contained in Danshen. The pharmacological tests revealed that tanshinones can dilate coronary arteries, increase coronary flow and protect the myocardium against ischaemia. Some of them have also been used to treat neurasthenic insomnia. In addition, tanshinones have attracted particular attention because they exhibit significant antibacterial, antioxidant, and antitumor activities. And among them, the most abundant and structurally representative bioactive component in the fraction is tanshinone IIA (TS IIA) (Fig. 1). Then TS IIA is selected as the marker component for the quality control of Danshen and Fufang Danshen tablet in the Chinese Pharmacopoeia (2005). However, TS IIA’s bioavailability is very low, which results in difficulties in its gastrointestinal formulation. Cyclodextrins are cyclic oligosaccharides, containing at least 6 d-( )-glucopyranose units attached by a-1,4-linkage. b-Cyclodextrin appears to be the best natural cyclodextrin due to its cavity size, efficient drug complexation, availability in pure form, and relatively low cost. Natural cyclodextrins can be modified to improve the low aqueous solubility. One of the pharmaceutically important cyclodextrin derivatives is 2-hydroxypropyl-b-cyclodextrin (HP-b-CD), which has greater solubilizing capacity and improved safety feature than the parent compound. More and more studies also applied HP-b-CD to improve the solubility, dissolution rate and the oral bioavailability of drugs. The present study is to find the absorptive rate-limiting step of TS IIA via investigating its absorption behavior and to gain a reasonable explanation for the cause leading to low oral bioavailability. Thereafter, we prepared complexation of TS IIA with HP-b-CD by coevaporation and characterized them by differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). The absorption properties of TS IIA from its inclusion complex in rats were investigated. We hope that this research could establish a base for investigating the absorption of the complexation of TS IIA with HP-bCD in vivo and finding an optimum pharmaceutical carrier for developing the oral preparation of TS IIA.