Studies on controlled release of indomethacin from PVA hydrogel

The polyvinyl alcohol (PVA) hydrogel containing 1-methyl-2-pyrrolidinone (MP) and sorbitol was preapred by the freeze and thaw method. The release rate of indomethacin from PVA hydrogel was used as a criterion for deciding the optimum formula of hydrogel using the computer optimization technique. The hydrogel of optimum formula was composed of PVA (10 w/v%), MP (0 w/v%), and sorbitol (40 w/v%) and the release rate of indomethacin was 1.981 μg/ml·min^1/2.     

Design of a polyvinyl alcohol hydrogen containing phospholipid as controlled-release vehicle for rectal administration of (+/-)-propranolol HCl

Polyvinyl alcohol hydrogels which contained phospholipid, egg yolk lecithin or hydrogenated soya lecithin were designed as a transrectal delivery system for propranolol hydrochloride. The hydrogel preparations containing phospholipid were prepared by a low-temperature crystallization method. The release profile of propranolol from hydrogel preparations containing phospholipid complied with Fickian diffusion (Higuchi model). The release of propranolol from the hydrogel preparation decreased with higher contents of phospholipid (approximately 2% w/w). In rats plasma concentrations of propranolol after rectal administration of hydrogel preparations containing phospholipid (1 and 2% w/w) were prolonged compared with those of rats receiving preparations without phospholipid.     

Novel chronotherapeutic rectal aminophylline delivery system for therapy of asthma

The aim of this study was to develop a new chronotherapeutic pharmaceutical preparation as a sustained-release suppository for prevention and therapeutic use against bronchial asthma in the early morning. Sustained-release hollow-type (SR-HT) suppositories using sodium alginate (Alg-Na), sodium polyacrylate (PANa) or polyacrylate-PANa co-polymer (PA-PANa) as gelling polymers (gel agent) were prepared and pharmaceutical characteristics of these suppositories were investigated. Type A SR-HT suppositories comprised a suppository shell prepared with oleaginous base and containing aminophylline only or aminophylline with Alg-Na or PANa in the cavity (hollow space). Type B SR-HT suppositories comprised a suppository shell prepared with oleaginous base and gel agent (30%), with aminophylline in the hollow space. In drug-release studies, the acrylate polymer-containing suppositories showed linearity of delayed release rate, providing significantly decreased the highest concentration of theophylline in plasma (C_max) and delayed the time required to reach C_max (t_max) and the mean residence time (MRT) after rectal administrated in rabbits. In particular, suppositories containing PA-PANa maintained significantly higher theophylline concentrations than control suppositories at 12 h after rectal administration. Furthermore, histopathological examination indicated that these suppositories using acrylate polymers did not result in rectal lesions. The SR-HT suppository, particularly using PA-PANa as a gel agent, may thus be useful against nocturnal symptoms of asthma. In this study, we confirmed new formulation of sustained-release suppository for chronotherapy of theophylline using oily base material in combination with polymer such as PA-PANa. The hollow-type suppository containing oleaginous base and hydrophilic polymer in the shell could be useful device for rectal administration of various drugs with prolongation of plasma concentration.     

Irinotecan-encapsulated double-reverse thermosensitive nanocarrier system for rectal administration

Intravenously administered for the treatment of rectum cancer, irinotecan produces severe side effects due to very high plasma concentrations. A novel irinotecan-encapsulated double reverse thermosensitive nanocarrier system (DRTN) for rectal administration was developed as an alternative. The DRTN was fabricated by dispersing the thermosensitive irinotecan-encapsulated solid lipid nanoparticles (SLN) in the thermosensitive poloxamer solution. Its gel properties, pharmacokinetics, morphology, anticancer activity and immunohistopathology were assessed after its rectal administration to rats and tumor-bearing mice. In the DRTN, the solid form of the SLN and the liquid form of the poloxamer solution persisted at 25?°C; the former melted to liquid, and the latter altered to gel at 36.5?°C. The DRTN was easily administered to the anus, gelling rapidly and strongly after rectal administration. Compared to the conventional hydrogel and intravenously administered solution, it retarded dissolution and initial plasma concentration. The DRTN gave sustained release and nearly constant plasma concentrations of irinotecan at 1–3?h in rats, resulting in improved anticancer activity. It induced no damage to the rat rectum and no body weight loss in tumor-bearing mice. Thus, this irinotecan-encapsulated DRTN associated with a reduced burst effect, lack of toxicity and excellent antitumor efficacy would be strongly recommended as a rectal pharmaceutical product alternative to commercial intravenous injection in the treatment of rectum and colon cancer.     

Bioavailability of indomethacin after intramuscular injection and rectal administration of solution and suppositories

The pharmacokinetics of indomethacin was studied after intravenous and intramuscular injection of 50 mg and administration of rectal solution and suppositories of 100 mg to 8 volunteers. Peak plasma concentrations of indomethacin occurred 20 min. after administration of the rectal solution (3.7 micrograms X ml-1), 40 min. after intramuscular injection (2.7 micrograms X ml-1), and 60 min. after suppositories (3.7 micrograms X ml-1). The bioavailability after the two rectal forms was found to be almost the same, about 80%. After intramuscular injection the bioavailability was calculated to be complete. These results suggest that indomethacin administered as a rectal solution or as intramuscular injection may be an alternative to intravenous administration when an early plasma peak of the drug is required.     

Pharmacokinetic Analysis of an Oral Sustained-Release Diltiazem Preparation Using Multifraction Absorption Models

Application of multifraction absorption models to pharmacokinetic analysis of an oral sustained-release diltiazem preparation (HER-SR) was investigated. The plasma diltiazem concentrations after oral administration of the HER-SR preparation were analyzed using both the two-fraction absorption model and the two-step discontinuous absorption model. The two-fraction absorption model was suitable for the pharmacokinetic analysis of the HER-SR preparation, whereas the two-step discontinuous absorption model is often unsuitable for the analysis of sustained-release preparations which disintegrate into fractions with different release characteristics in the gastrointestinal tract. The two-step discontinuous absorption model is usually not applicable to plasma concentration data when the first peak is sharp. MFA-MULTI(V) was shown to be useful for the prediction of the bioavailability in each fraction of HER-SR. It was further demonstrated that a two-fraction absorption model is useful for the comparison of in vitro and in vivo release profiles or evaluating the influence of food on the absorption behavior of HER-SR. In addition, the application of a two-fraction absorption model to population pharmacokinetics of HER-SR was investigated.     

Poly(D,L-lactide-co-glycolide) encapsulated poly(vinyl alcohol) hydrogel as a drug delivery system

Purpose. The efficiency of encapsulation of water-soluble drugs in biodegradable polymer is often low and occasionally these microcapsules are associated with high burst effect. The primary objective of this study is to develop a novel microencapsulation technique with high efficiency of encapsulation and low burst effect. Method. Pentamidine was used as a model drug in this study. Pentamidine/polyvinyl alcohol (PVA) hydrogel was prepared by freeze-thaw technique. Pentamidine loaded hydrogel was later microencapsulated in poly(lactide-co-glycolide) (PLGA) using solvent evaporation technique. The microcapsules were evaluated for the efficiency of encapsulation, particle size, surface morphology, thermal characteristic, and drug release. Results. Scanning Electron Microscope (SEM) studies revealed that the microcapsules were porous. The microcapsules were uniform in size and shape with the median size of the microcapsules ranging between 27 and 94 m. The samples containing 10% PLGA showed nearly three times increase in drug loading (18-53%) by increasing the hydrogel content from 0-6%. The overall drug release from the microencapsulated hydrogel, containing 3% and 6% PVA, respectively, was significantly lower than the control batches. Conclusions. The use of a crosslinked hydrogel such as PVA can significantly increase the drug loading of highly water-soluble drugs. In addition, incorporation of the PVA hydrogel significantly reduced the burst effect and overall dissolution of pentamidine.     

Effect of sodium carboxymethylcellulose and fucidic acid on the gel characterization of polyvinylalcohol-based wound dressing

The purpose of this study was to investigate the effect of sodium carboxymethylcellulose (Na-CMC) and fucidic acid on the gel characterization for the development of sodium fucidate-loaded wound dressing. The cross-linked hydrogel films were prepared with polyvinyl alcohol (PVA) and sodium carboxymethylcellulose (Na-CMC) using the freeze-thawing method. Their gel properties such as gel fraction, swelling, water vapor transmission test, morphology, tensile strength and thermal property were investigated. In vitro protein adsorption test and release were performed. Na-CMC decreased the gel fraction and tensile strength of the hydrogels, but increased the swelling ability, water vapor transmission rate, elasticity and porosity of hydrogels. Thus, the wound dressing developed with PVA and Na-CMC was more swellable, flexible and elastic than that with only PVA because of its cross-linking interaction with PVA. However, the drug had a negative effect on the gel properties of hydrogels but there were no significant differences. In particular, the hydrogel composed of 2.5% PVA, 1.125% Na-CMC and 0.2% drug might give an adequate level of moisture and build up the exudates on the wound area. Thus, this sodium fucidate-loaded hydrogel could be a potential candidate for wound dressing with excellent forming.     

Rectal bioavailability of lidocaine from a suppository and a slow release preparation in man

In a previous investigation it was shown that the systemic availability of lidocaine in humans following rectal administration of an aqueous solution was about twofold higher than after oral administration. Most likely this was due to a partial avoidance of hepatic ‘first-pass’ metabolism. In the present study the systemic availability of two different rectal dosage forms of lidocaine was examined. Six healthy volunteers received in a balanced cross-over design a rectal capsule with slow release granules and a suppository, both containing 300 mg lidocaine as lidocaine. HCl. Plasma concentrations were measured for 8 h after drug administration by capillary gas chromatography. The mean rectal systemic availability of the two preparations was not significantly different: 49% (suppository) and 54% (capsule), when compared to the results obtained in a previous investigation after intraveneous administration. Early defaecation occasionally caused a loss of still unabsorbed drug. Mean bioavailability of the rectal aqueous solution was 70%. As expected, the absorption from the suppository was more rapid than from the capsule: the mean peak times were 122 min and 195 min respectively (p < 0.05). The mean maximum plasma concentrations were comparable: 0.70Μg/ml (suppository) and 0.69Μg/ml (capsule) respectively. These results confirm the previous findings that rectal administration of lidocaine results in a higher systemic availability than oral administration, but they are at the same time rather variable with the dosage forms studied.     

Calcein Release from Polymeric Vesicles in Blood Plasma and PVA Hydrogel

Purpose  The main goal of this study was to show the long-term stability of vesicles from poly(2-methyl oxazoline-block-polydimethylsiloxane-block poly(2-methyl oxazoline) (PMOXA-PDMS-PMOXA) in PBS, blood plasma and the feasibility to use these vesicles for drug release from PVA hydrogels. Methods  The vesicle formation properties and loading efficiency was evaluated using fluorescent dyes. The stability of the vesicles was evaluated in buffer at pH 7 at room temperature and in 50% blood plasma at 37°C. The calcein loaded vesicles were dispersed in a UV crosslinked PVA hydrogel. The stability of the vesicles in the hydrogel was observed over one week, before the vesicles were ruptured with Triton X-100. Results  The vesicles are very stable in buffer, blood plasma, and the PVA hydrogel. In plasma 50% of the calcein is released in 48 h in the presence of sodium azide. The vesicles can be evenly dispersed in PVA and are stable. The release can be triggered and the calcein diffuses afterwards quickly throughout the gel. Conclusion  Polymeric vesicles can be used as diffusion barrier in hydrogels for the controlled release of water soluble drugs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of Peptide Loading and Surfactant Concentration on the Characteristics of Physically Crosslinked Hydrogel

The purpose of this study was to investigate the effect of varying drug load and concentration of a surfactant (sodium lauryl sulfate [SLS]) on the release characteristics of a model peptide (bovine serum albumin [BSA]), and study the net effects of the swelling properties of the hydrogel matrix [poly(vinyl alcohol) (PVA)]. The PVA hydrogel was prepared by a freeze-thaw process in the absence of a chemical crosslinking agent. The effect of protein loading on drug release was examined at three levels (0.65, 1.3, and 2%), whereas the effect of SLS was studied at four levels (0, 0.07, 0.13, and 0.26%). The baseline time for reaching equilibrium swelling was 48 hr for the hydrogel containing 0.65% BSA, and the equilibrium swelling time decreased significantly as the protein load was increased to 2%. The net effect of increased BSA concentrations resulted in faster BSA dissolution from the hydrogel matrix. The equilibrium-swelling ratio decreased from 21 to 10% when SLS was added to the PVA solution, which resulted in a reduction in the extent of equilibrium swelling; however, the time to reach equilibrium swelling was increased. The investigation provided a mechanistic basis toward the development of a hydrogel formulation by altering the concentration of two fundamental components, i.e., drug and surfactant, within the delivery system.     

Effect of peptide loading and surfactant concentration on the characteristics of physically crosslinked hydrogel

The purpose of this study was to investigate the effect of varying drug load and concentration of a surfactant (sodium lauryl sulfate [SLS]) on the release characteristics of a model peptide (bovine serum albumin [BSA]), and study the net effects of the swelling properties of the hydrogel matrix [poly(vinyl alcohol) (PVA)]. The PVA hydrogel was prepared by a freeze-thaw process in the absence of a chemical crosslinking agent. The effect of protein loading on drug release was examined at three levels (0.65, 1.3, and 2%), whereas the effect of SLS was studied at four levels (0, 0.07, 0.13, and 0.26%). The baseline time for reaching equilibrium swelling was 48 hr for the hydrogel containing 0.65% BSA, and the equilibrium swelling time decreased significantly as the protein load was increased to 2%. The net effect of increased BSA concentrations resulted in faster BSA dissolution from the hydrogel matrix. The equilibrium-swelling ratio decreased from 21 to 10% when SLS was added to the PVA solution, which resulted in a reduction in the extent of equilibrium swelling; however, the time to reach equilibrium swelling was increased. The investigation provided a mechanistic basis toward the development of a hydrogel formulation by altering the concentration of two fundamental components, i.e., drug and surfactant, within the delivery system.     

Jejunal Absorption,Pharmacological Activity,and Pharmacokinetic Evaluation of Indomethacin-Loaded Poly(d,l-Lactide) and Poly(Isobutyl-Cyanoacrylate) Nanocapsules in Rats

The jejunal absorption of indomethacin nanocapsules was studied using an in vivo infusion technique. Jejunal absorption of indomethacin from the nanocapsules was slightly delayed as compared to a commercial indomethacin solution. The plasma and jejunal mucosa indomethacin concentrations were similar in both cases. However, the nanocapsules protected the rat jejunum from the ulcerating effect of indomethacin, probably by avoiding direct contact of the free drug with the surface of the mucosa. The pharmacokinetic profile of indomethacin nanocapsule formulations was compared to a solution of free drug following oral administration of 5 mg/kg in rats; no difference in the mean concentration–time profiles of the drug was observed. Blood levels of thromboxane showed a sustained biological activity, over a period of 24 hr, of indomethacin-loaded nanocapsules, relative to the drug in solution, following oral administration.     

青藤碱固体脂质纳米粒凝胶骨架缓释片的制备及处方优化

目的：制备青藤碱固体脂质纳米粒凝胶骨架缓释片,考察凝胶骨架缓释片处方因素对青藤碱固体脂质纳米粒体外释药行为的影响。方法：采用乳化蒸发-低温固化法制备青藤碱固体脂质纳米粒。以羟丙基纤维素（HPMC）为骨架材料制备青藤碱固体脂质纳米粒凝胶骨架缓释片,单因素考察吸附剂种类、骨架材料比例、PEG种类和骨架材料用量对缓释片体外释药的影响,正交试验进一步优化处方,并对释药模型进行拟合。结果：骨架材料比例和PEG种类是影响青藤碱固体脂质纳米凝胶骨架缓释片体外释药行为的主要影响因素,优化后的处方体外释放行为符合一级释药模型,释药方程为ln（1-M_t/M_∞）=-0.187 2 t+0.071 2（r=0.991 1）,累积释放度在12 h内可达90.15%。结论：优化后的青藤碱固体脂质纳米粒凝胶骨架缓释片制备工艺简单,重复性良好,在12 h内具有良好的体外缓释特征。     

Influence of Indomethacin Amphoteric Gel on Gastric Ulcerogenicity and Absorption of Indomethacin in Rats

Indomethacin is a potent and efficacious antiinflammatory agent. However, a limiting side effect is its ability to cause gastric ulceration. This study was designed to investigate the effects of an amphoteric gel on the gastric ulcerogenicity and pharmacokinetics of indomethacin. Oral administration (5 mg/kg) in a suspension and a gel formulation were compared to an intravenous (iv) formulation of indomethacin in rats. The iv formulation administered to rats produced large severe ulcers in some rats but not in others. In contrast, the oral suspension produced small ulcers in all rats. The difference in toxicities is attributed to a centrally mediated action as a result of high plasma levels of indomethacin following iv administration, compared to locally mediated action with the suspension, resulting from local high concentrations of indomethacin on the apical epithelial surface because of the presence of indomethacin crystals. Oral administration of the gel formulation did not result in any gastric ulceration and improved the bioavailability of indomethacin to 115.5%, compared with 68.2% for the suspension. The reduced gastrointestinal toxicity of indomethacin in the gel was attributed to the gel's ability to dissolve indomethacin, preventing the localized high concentration observed with the suspension and possibly providing a gastric protectant phospholipid. The gel formulation doubled the oral bioavailability and the t _max of indomethacin compared to the suspension but did not affect the half-life. The results indicate that the local irritant effect of indomethacin, in rats, can be reduced by appropriate formulation design and suggest that the ulcerogenicity index for indomethacin can be improved by the use of an amphoteric gel formulation.     

Pharmacokinetic interactions between indomethacin and paracetamol in the rat

The influence of concurrent administration of paracetamol with indomethacin on the plasma concentrations of these drugs was studied in rats. Orally administered paracetamol reduced the plasma levels of indomethacin during the first 2 hours after oral administration. Later, 16 and 24 hours after administration of indomethacin, the plasma levels exceeded the control values due to the concurrent oral administration of paracetamol. These data suggest that paracetamol delayed the absorption of indomethacin. In contrast the plasma concentrations of paracetamol were not influenced substantially by indomethacin. When paracetamol was co-administered subcutaneously with oral indomethacin, the plasma levels of the latter drug were not influenced. It is concluded that the protective effect of paracetamol against the gastric injuring side effect of indomethacin, which also occurs with subcutaneous administration of paracetamol, cannot be solely due to lowered plasma concentrations of indomethacin.     

Kinetics of indomethacin absorption,elimination, and enterohepatic circulation in man

There are no discernible quantitative differences in the biotransformation and the excretion of indomethacin following oral, rectal, and intravenous administration of indomethacin-¹⁴ C. Approximately 50% (range 24–115% for n=6) of an intravenous dose undergoes enterohepatic circulation. Thus the bioavailability of indomethacin to the systemic circulation may exceed the administered dose. Relative to the intravenous dose, indomethacin is 80 and 100% bioavailable from suppositories and capsules, respectively. Absorption and/or reabsorption appears to be more rapid and uniform by the rectal route. Recognition of the attributes of biliary recycling also helps to explain the observed variability in apparent plasma half-life, while their neglect requires alternative explanations for anomalies between the disappearance rate from plasma and the corresponding appearance rate in urine.     

阿立哌唑缓释微球的工艺优化及体内药动学研究

目的:制备阿立哌唑缓释微球,使用星点设计-效应面法优化工艺,并对其体内血药浓度进行分析。方法:采用乳化溶剂挥发法制备阿立哌唑微球;以油相二氯甲烷体积、水相聚乙烯醇质量分数及乳化转速为自变量,以微球的平均粒径、跨距、载药量、包封率、产率及突释量为因变量,对制备工艺进行优化,并对优化后的工艺进行验证。采用HPLC法测定家兔血浆中药物浓度。结果:最佳工艺为二氯甲烷体积1.62mL,聚乙烯醇质量分数1.91%,乳化转速2 161 r.min-1;按优化工艺制备的微球外观圆整、流动性好;平均粒径为41.54μm,跨距为1.01,载药量为18.82%,包封率为75.39%,产率为85.17%,突释为1.68%。自制微球制剂在家兔体内d 1有少量的突释,d 5～d 20维持较稳定的血药浓度,缓慢释放,之后浓度开始下降。结论:所优化的制备工艺重现性好,简单易行;星点设计-效应面法优化微球制备工艺预测性良好,所制备的微球具有较好的体外缓释特性;阿立哌唑缓释微球在家兔体内缓慢释放,该释药行为达到了预期的目的。     

Interaction of indomethacin and acetylsalicylic acid as shown by the serum concentrations of indomethacin and salicylate

Summary A clinical-pharmacological study was performed to determine the effect of acetylsalicylic acid upon the serum concentration of indomethacin. 14 rheumatic patients were given indomethacin orally (25 mg × 4 for 4 days) and concurrently acetylsalicylic acid 3.7 g orally (0.9 g × 3 and 1.0 g × 1 daily), and 21 rheumatic patients were given indomethacin rectally in the morning (100 mg × 1) and concurrently acetylsalicylic acid 3.7 g orally (0.9 g × 3 and 1.0 g × 1 daily). On comparison with treatment with oral or rectal indomethacin alone, it was found that peak serum concentrations of indomethacin were significantly reduced (1% level), the times of the peaks were not shifted, and the areas beneath the serum concentration curves of indomethacin were smaller, but significantly so only if compared with rectal administration. In 12 rheumatic patients given indomethacin by rectum in the evening (100 mg × 1) and concurrently acetylsalicylic acid 3.7 g (0.9 g × 3 and 1.0 g × 1 daily), the serum level of indomethacin on the following morning (after 11 h) did not differ from that found after rectal treatment. A statistically but not biologically significant difference was observed between the mean serum half-lives of indomethacin given orally and rectally. For unknown reasons, concurrent doses of acetylsalicylic acid and indomethacin made the mean serum half-life of indomethacin longer than after its oral administration, but shorter than when the same dose of indomethacin was given rectally. There was no difference between serum levels of salicylate after oral administration of acetylsalicylic acid alone or after a concurrent oral or rectal dose of indomethacin. The results have been related to those reported previously, with respect to the interaction between indomethacin and acetylsalicylic acid, the serum levels of indomethacin after oral and rectal dosing, and the serum half-life of indomethacin based upon a one- or two-compartment model. The clinical relevance of the study is discussed.     

Indomethacin distribution in acute pharmacological response among rats

A detailed examination of quantitative relationships of pharmacological action with plasma and tissue concentrations of indomethacin has been undertaken in the rat, after single oral administration of two sustained release preparations. In this study, drug was assayed by high performance liquid chromatography, whereas antiinflammatory response was assessed through the carrageenin-induced edema test. Significant linear correlations (p less than 0.001) were found between logarithmically transformed percent inhibition of edema and logarithmically transformed plasma, as well as tissue levels of indomethacin. However, the lack of significance for partial correlation regarding tissue concentration, contrary to plasma concentration, suggests that pharmacological response is more closely related to the latter, indicating that antidematous effect is mediated via the circulating drug rather than a local action in target tissues. This assumption is further discussed from the equivalence point of view. The relevance of this type of study in the case of topical administration of indomethacin is addressed as well. Taking into account the predictive value of the rat paw edema test for clinical efficacy, relationships similar to those observed are to be expected in man. The high correlation existing between plasma concentration of indomethacin and its pharmacological effect justifies the development and use of sustained release preparations in order to improve the outcome of treatment with this nonsteroidal antiinflammatory drug.