The Preparation Of Bioadhesive Sustained-release Capsule Of Captopril And Its Evaluation In Vivo And In Vitro

Captopril(Cap) , (l-[(2s)-3-mercapto-2-methyl propionylpropionlyl]-L-proline). a first invented inhibitor of angiotensin-converting enzyme(ACE) in the world and freely soluble in water, has been considered as one of the first line drugs in the treantment of hypertention and congestive heart failure due to its effectiveness and low toxicity. However, the patients, who has taken excessive dose of Cap resulted in the peak-gorge phenomenon arisen from the fact that the oral administration of drug every 6-8 hour produce the maintenance of effective blood concentration for which the elimination half life of the free drug was in the range of 1-3 h, might suffer from dizziness or headache( Therapeutic blood concentration of Cap: 50μg/ml, po 50 mg, C_max: 600μg/ml). Beside that the drug shows a mixed type of absorption from the GIT(being passively absorbed in part and through the peptide-carrier mediated in the other part). The drug also sustain dose dumping and burst phenomenon (being freely water soluble) when formulate as sustained or controlled release formulation. On the other hand, the drug is subjected to instability in the stomach and small intestine and reflects prominent food reactions and its bioavailability decreases in the presence of food. Despite numerous attempts and works to be made to regulate the release process by the preparation of the sustained-release coated tablets, microcapsules and hydrogel plug pulsatile delivery system of Cap with microcrystalline cellulose, ethyl cellulose and polyvinylpyrrolidone, very few have been successful. The clinical supportive data in relation to the efficacies of these developed formulations are not always available, and their claims rely on in vitro data. The main objective of this project is to develop captopril/bioadhesive sustained-release systems in order to improve thetherapeutic efficiency, decrease the side effects of Cap, find a novel experimental and theoretic bases to develop an ideal sustained release system for water-soluble drugs according to principles and methods of modern pharmaceutics and conduct evaluation on it in vivo and in vitro.The captopril/chitosan-gelatin net-polymer microspheres (Cap/CGNPMs) were manufactured by the methods of emulsification and cross-linking with natural and decomposed chitosan and getalin. In vitro evaluation for Cap/CGNPMs were carried out by optical and scanning electron microscopy and UV spectrometry. Fractional factor design was applied to optimize the formulation and preparation procedure of Cap/CGNPMs. The results indicated that Cap/CGNPMs had a spherical shape , smooth surface morphology and integral inside structure and no adhesive phenomena and good mobility. Researches on the release of Cap from the microspheres in vitro demonstrated that Cap/CGNPMs was of the role of retarding release of Cap compared with Cap ordinary tablets (COT). The embedding ratio (ER) , drug loading (DL) , swelling ratio (SR) and release behaviors of CGNPMS were influenced by process conditions of preparation such as experimental material ratio (EMR) , composition of cross linked reagents. Among these factors, chitosan molecular weight (700,000 Da), the experimental material ratio (EMR, 1/4), cross linked reagents (CLR, For+TPP) ,cross linked level (CLL, 1:0.75) and 0.75% microcrystalline cellulose (MCC) added to the microspheres were the optimal scheme to the preparation of Cap/CGNPMs. The size and distribution, embedding ratio and drug loading of Cap/CGNPMs were 220-280 U m, 46.23 ± 4.51% and 9.95 ± 0.77% respectively. The results also demonstrated that the process of emulsification and cross-linking process were simple and stable.The results of stability test revealed that there were no significant change of the shape, the particle size and the DL and drug release behavior of these Cap/CGNPMs stored at temperatures and humidity of 4, 25, 40°C/RH75% for 3 months respectively.To further increase bioavailability of captopril and control dose dumping and burst phenomenon (being freely water soluble) when formulate as sustained or controlled release formulaftion, the captopril/bioadhesive sustained-release capsules( CBSRCs) were prepared by the method of wet granulation on the basis of the results of Cap/CGNPMs. Attempts to retard the gastrointestinal retention time and enhance the bioadhesion for CBSRCs to obtain a specific drug delivery system have been carried out by taking advantage of dual action of bioadhesion and drug sustained release of hydroxypropoxyl methyl cellulose(HPMC ) and drug sustained release of CBSRCs. Factorial design was applied to optimize the formulation and preparation procedure of CBSRCs. The effect of different variables on the release in vitro and the characterization of CBSRCs were investigated according to a factorial design of experiments. The results indicated that the CBSRCs had adhesive characteristics on gastrointestinal mucosa in vitro. The adhesive force of CBSRCs to gastrointestinal mucosa was positively correlated with the content of HPMC, negatively correlated with the content of the fillers such as calcium carbonate and magnesium carbonate. The drug release experiment in vitro confirmed that the CBSRCs had sustained-release behavior compared with COT and the release velocity of Cap was positively correlated with the content of HPMC. The dissolution curve in vitro of Cap from CBSRCs showed that the drug release could be best described by the Higuchi equation and could expressed by following equation: Q = 11.4870 tm - 1.1415, R2 =0.9817 , which suggested that the release profiles of Cap from CBSRCs were coupled with diffusion and bulk erosion model.The pharmacokinetic study were carried out in rabbits with high-performance liquid chromatography (HPLC ) for the improvement of formulation and clinical use of drug. A novel determination process of blood concentration of Cap in rabbits was established with HPLC-uv-vis Detector. Linear calibration curves of Cap was described as following: y =0.0065x-0.0382, R2 = 0.9987. Minimum detectable concentration was 6 ug/ml. Mean recovery was 99.62% for both Cap and internal standard. The variation of recovery between different concentration of Cap andinternal standard were both < 5% (n = 7). Mean relative standard deviation (interday) was 7.13%(n = 7). Mean relative standard deviation (day to day) was 8.37%(n = 7). The results showed that the process o f determination with HPLC was stable and reliable results can be obtained.Ten New Zeland rabbits were given orally CBSRCs and COT following a single dose of 60 mg Cap in an open randomized crossover study. The plasma concentration of Cap was measured by HPLC and the pharmacokinetics parameters were calculated with 3p97 program. The concentration-time curves of CBSRCs and COT fitted to one-compartment open model respectively. The major pharmacokinetics parameters of CBSRCs and COT were showen respectively as following: Tmax(h) 2.9244 ± 0.2561 and 1.1344 ± 0.2196; Cmax(ng/ml) 648.9709 ± 33.6848 and 1094.4740 ± 108.3554; ka (IT1) 0.5369 ± 0.0778 and 1.8869 ± 0.4670; AUC0., [(ug/ml) ?h] 5058.0249 + 335.4599 and 4698.2998 ± 815. 4933; AUC0-co [(ug/ml) ? h] 6429.3882 ± 1337.5759 and 4846.8311 ± 874.5589; MRT (h) 5.0996 ±0.3330 and 3.3145 ±0.3586. The relative bioavailability of the CBSRCs were 110.98 ± 22.96% calculated in light of data of AUCo-t of two formulations. There were significant differences between AUCo-t, AUCo^? Ka, Cmax, Tmax, MRT of CBSRCs and COT(P < 0.01 or 0.05) and the CBSRCs showed no bioequivalence compared with the COT.From the results above mentioned, we drew such conclusion that the Cap/CGNPMs had a characteristics of sustained release of drug and the process of emulsification and cross-linking process were simple and stable. The size and distribution, ER and DL of Cap/CGNPMs prepared according to the optimal scheme were stable and the process of preparation was reliable. The CBSRCs had good adhesive characteristics on gastrointestinal mucosa in vitro. The CBSRCs, prepared by the process of bioadhesion and sustained-release, Has a high bioavailability in rabbits than COT.In short, this bioadhesive sustained-release system provides promising new alternative for the delivery of water-soluble drug to produce prolonged acting time and decrease side effects.