DESIGNING OF MULTIPARTICULATE ORAL DELIVERY OF COLON SPECIFIC ANTIARTHRITIC DRUGS: SCREENING OF FORMULATION VARIABLES AND INVITRO-INVIVO INVESTIGATIONS
Author: Bankim Chandra Nandy
Supervised by Dr. Bhaskar Mazumder, Assistant Professor, Department of Pharmaceutical Sciences, Dibrugarh University, Dibrugarh, Assam, India
The colon is a site where both local and systemic delivery of drugs can take place. Colon-specific systems could also be used in diseases that have diurnal rhythms.
The aimed of this work reported here was to design, develop and optimize multiple-unit colon-specific formulations for oral administration, using enteric polymers as the relevant excipients. It was aimed to prepare a formulation that allows drug absorption after a lag time of about 4-5 hours. The idea was that the enteric polymers would prevent drug release and absorption in the upper gastrointestinal tract.
Indomethacin and celecoxib were used as model drugs. The present research work was divided into two parts i.e. Experiment I and II; to fulfill the above objectives. These experiments were mainly emphasized to develop an effective and potential delayed release system to satisfy the desired target. This colon specific delivery of celecoxib (Experiment I) and indomethacin (Experiment I) may use for both local (in prophylaxis of colorectal adreno-carcinoma) and systemic (in chrono-therapeutic treatment of arthritis) therapy. The formulations simultaneously benefits the delivery of drug in its intact form to the target site, leading to reduce dose related side effects, improve the oral bioavailability by increasing the residence time in colon and reduce the total dose.
Both the experiments were designed according to a three levels face centered central composite design. Microspheres were formulated with the combination of ethyl cellulose (EC) and eudragit RS100/S100; by using a novel quasi emulsion solvent diffusion technique. The aim of the present work was to elucidate the effect of formulation variables e.g., amount of eudragit polymer (X1), surfactant concentration (X2) and agitation speed (X3) on in-vitro release profiles (Y1-Y3), drug entrapment efficiency (Y4) and particle size (Y5) of multi-particulates system of indomethacin and celecoxib. Developed formulations were characterized and evaluated on the basis of drug polymer interaction study by means of FTIR and DSC study, drug content, particle size, shape, surface characteristics by SEM analysis, XRD analysis and swelling behavior of microspheres. In vitro dissolution & drug release kinetics studies were also carried out. For in vitro release study different solvent systems such as 0.1 N hydrochloric acid (pH 1.2), phosphate buffers pH 6.8 with surfactant and phosphate buffers pH 7.4 with surfactant were used for better simulation and prediction of in vivo release behavior. On the basis of various parameters of dependent and independent variables of the formulations; it was further optimized by Response surface methodology through Design Expert software (Version 18.104.22.168 Trial, Stat-Ease Inc, Minneapolis, Minnesota). Optimized delayed released system was further subjected to evaluate the stability, pharmacokinetic & x-ray studies.
Indomethacin is a widely used non-steroidal anti-inflammatory drug (NSAID) and extensively prescribes for treatment of arthritis. Delayed action (at the morning or night) is needed for arthritic patients.
In presence of 0.1 N HCl solutions, cumulative drug released for first two hours from RIF & SIF formulations was varied between 6.00 ±1.04 to 15.05 ±1.44 % & 1.20±0.28 to 3.00±0.94 % respectively, but cumulative drug released at 5 hrs in phosphate buffer (pH 6.8) dissolution medium was 36.20 ±1.28 to 54.35 ±2.24 % & 21.85 ±1.22 to 33.20 ±2.40 % in that order and cumulative released of drug after 9 hrs ranged from 72.70 ±2.14 to 96.60 ±2.86% & 81.80 ±2.44 to 96.80 ±2.44 % correspondingly. In case of RIF13 microspheres the highest correlation coefficient was obtained in Higuchi model (0.98) than zero and first order. For SIF13 microspheres the highest correlation coefficient was obtained in zero order model (0.96) than Higuchi and first order model. For both these selected formulations the ‘n’ value from Peppas model was indicating that formulation follows Fickian diffusion controlled release.
For the delivery of maximum amount of indomethacin in intact form to the colon, this approach suggested that the combination of EC and eudragit S100 microspheres may be useful in a better way compared to formulations prepared with EC and Eudragit RS100.
On the basis of optimization parameters, RIF13 and SIF13 were selected as a best multi-particulates system and which may fulfill the desired target. In case of RIF13 & SIF13 microspheres, the cumulative amount of drug released at 120 min in 0.1N hydrochloric acid were 10.20 ±1.46% and 1.50±0.26%; while indomethacin released from RIF13 the microspheres in simulated intestinal fluids i.e. phosphate buffer (pH 6.8) with 0.5 % SLS solutions was found 47.70 ±2.24 % of the loaded amount, but the drug released for SIF13 microspheres was 25.45 ±1.28 and the cumulative released of drug in simulated to colonic fluids (i.e. phosphate buffer solutions pH 7.4) at 9 hrs were 85.20 ±2.18% (RIF13) and 86.70 ±1.28% (SIF13). Time required to release 50% of initial amount of drug (t50%) from RIF13 & SIF13 formulations was approximately 305 min & 355 min. These two best selected formulations were further treated to carry out the stability study.
The stability studies of best formulations were carried out and there was no significant change in the drug contents and dissolution rate.
On the basis of above cited data of both RIF13 and SIF13 formulations, SIF13 was selected as a best suited formulation to fulfill the desired target. The in vitro released characteristics of drug from the SIF13 microspheres was further subjected for correlating with the in vivo data and for site specificity release; x-ray study was considered. In case of sustained release marketed product of indomethacin (Indocap-SR 75 mg caps.) the maximum plasma concentration; Cmax and the time to reach this maximum concentration; Tmax obtained from the individual plasma concentration time data were 1926.46 ± 255.46 ng mL-1 and 3.26 ± 1.12 h, respectively, while they were 2056.25 ± 1024.61 ng mL-1 and 6.24 ± 1.25 h, respectively, for the optimized formulation (SIF13). Statistical significant differences (p < 0.05) of AUC were found, and the relative bioavailability of SIF13 was 113%. The higher Tmax of SIF13 indicated that drug absorption took place after a lag time and a linear correlation (R2 = 0.9799, p<0.01) represent point-to-point relationship between in vitro release and in vivo absorption.
Finally the gastric resident time of optimized formulations were evaluated by conducting in-vivo X-ray studies in healthy rabbits. From in vivo X-ray studies, it was clearly observed that the microspheres showed a gastric residence of nearby 2 hrs.
This present study holds promise to improve patient compliance especially for arthritic patients. Following bedtime administration, microspheres are expected to maintain low drug plasma concentration overnight when the arthritic pain are reported to be the minimum and release the optimal concentrations in the morning between 6-9 hrs; when pain is found to be the maximum.
Celecoxib is an anti-inflammatory drug and especially used in arthritis. Celecoxib exhibits poor water solubility, with 6-11 hours biological half life. Conventional dosage form is administered twice daily to fulfill the therapeutic level of the patient. only 40% of administered drug is bioavailable through oral route and bioavailability may be greater if it is targeted to the colon. Celecoxib was selected as a model drug because it has good indication for colonic delivery. Being a very weakly acidic (pKa 11.1) & BCS class II drug, the bioavailability of celecoxib can be increased by targeting the drug into the colon and thus the solubility may be increased in presence of colonic environments.
Microspheres (RCF) prepared with EC & eudragit RS100, the range of particle size of d (0.5) and d (0.9) was 71.30±0.63 to 653.66±2.02 µm and 330.57 ±1.85 to 877.55 ±2.78 µm respectively. Particle size of d (0.5) and d (0.9) of microspheres (SCF) prepared with EC & Eudragit S100 was varied between 76.85±1.24 to 596.62±4.06 µm and 348.59 ±1.14 to 848.13 ±3.02 µm respectively.
On the basis of optimization parameters, RCF2, RCF14 and SCF7 were selected as a best multi-particulate system and which may fulfill the desired target. In case of RCF2, RCF14 and SCF7 microspheres the maximum cumulative amount of drug released at 120 min in 0.1N hydrochloric acid were 11.75 ±1.24%, 13.75 ±1.28% and 0.45 ±0.04% respectively; while celecoxib released from RCF2, RCF14 the microspheres in simulated intestinal fluids i.e. phosphate buffer (pH 6.8) with 0.5 % SLS solutions were found 41.55±2.15% and 44.10 ±1.06% of the loaded amount, but the drug released for SCF7 microspheres was 23.80±2.46%. The % cumulative released of drug in simulated to colonic fluids (i.e. phosphate buffer solutions pH 7.4) at 9 hrs was 81.10 ±2.60 (RCF2), 85.95±2.24 (RCF14) and 79.90 ±2.25 (SCF7). % entrapment efficiency of RCF2, RCF14 and SCF7 were 74.13 ± 1.04, 95.34 ±1.15 and 69.29 ±2.84 respectively and particle size [d (0.5)] was 106.35±1.98, 578.30±1.64 and 76.85±1.24 µm correspondingly. SCF7 microspheres showed the highest correlation coefficient in first order model (0.96) than zero and Higuchi order. Time require to release 50% of initial amount of drug (t50%) from RCF2, RCF14 and SCF7 formulations were approximately 316, 310 & 357 min. On the basis of above cited data of RCF2, RCF14 and SCF7 formulations, RCF2 & SCF7 were selected as a best suited formulation to fulfill the desired target and it was further treated to carry out the stability study, but out of these two formulations SCF7 was only chosen for further conducting the pharmacokinetics & x-ray study. The stability studies of best formulations were carried out and there was no significant change in the drug contents and dissolution rate.
From the individual plasma concentration time data for the conventional marketed product of celecoxib showed the maximum plasma concentration; Cmax and the time to reach this maximum concentration; Tmax at 868.26 ± 212.23 ng mL-1 and 2.802 ± 1.47 hrs., respectively, while they were 1060.44 ± 324.62 ng mL-1 and 6.67 ± 2.43 h, respectively, for the optimized formulation (SCF7). Statistical significant differences (p < 0.05) were found, and the relative bioavailability was 130%. Generally, significant differences were found in the pharmacokinetic parameters related to the rate and extent of celecoxib absorption from the optimized and marketed products. The higher Tmax indicated that drug absorption took place after a lag time of drug.
The gastric resident time of optimized formulation (SCF7) was evaluated by conducting in-vivo X-ray studies in healthy rabbits. From in vivo X-ray studies, it was clearly observed that the microspheres showed a gastric residence of nearby 2 hrs. As the swelling continued, the glassy core diminished, the swelling layer eroded from the outer surface and a size reduction was seen after 6 hrs when microspheres were reached into the site of colon.
Multi-particulates systems are expected to achieve maximum amount of drug release in early morning and which can provide adequate protection of rheumatoid arthritic patients by a bed time administration of these delivery system. This colon specific delivery of celecoxib may use for both local (in prophylaxis of colorectal adreno-carcinoma) and systemic (in chrono-therapeutic treatment of arthritis) therapy. However, the in vivo pharmacokinetics data and x-ray studies carried out in animal model of both the drugs from the microspheres are to be further subjected to clinical studies to prove the bioavailability of model drug in human beings.