Design of Chronomodulated Drug Delivery System of Valsartan: In Vitro Characterization

The aim of the present study was to design and evaluate a chronomodulated time-clock pulsatile tablets of valsartan to release it after a certain lag time, independent of the gastrointestinal pH, in its absorption window to cope with the circadian rhythm of human body for blood pressure elevation. Core tablets were prepared by direct compression of a homogenous mixture of valsartan, Avicel PH101, croscarmellose sodium, magnesium stearate and Aerosil. The core tablets were then sprayed coated with a sealing layer formed of ethyl cellulose that was subsequently coated with a release-controlling layer. Three different aqueous dispersions namely; carnauba wax or beeswax or a mixture in a ratio of 2.5:1, respectively, were used to form five time-clock tablet formulations having the release controlling layer with different thickness {B5, B10, B20, BW5 and CW5}. Quality control testing were carried out to the core tablets. Differential scanning calorimetry was also performed to detect the possible drug excipient interaction in the core tablet formulation. The release was carried out, for the prepared time-clock tablet formulations, in 0.1 N hydrochloric acid for the first 2 h, followed by phosphate buffer (pH 6.8) for 4.5 h. The effect of pH on valsartan release was studied through a release study in 0.1 N hydrochloric acid for 6.5 h. Two phase dissolution study was performed to the selected time-clock tablet formulation to predict the drug permeation through the gastrointestinal tract. Stability study of the selected formula was performed at 25°/60% RH and at 40°/75% RH for 3 months. Results showed that a release-controlling layer composed of a mixture of carnauba wax and beeswax in a ratio of 2.5:1 showed a reasonable release lag time. The release lag time of the tablets increased with the increase of the coat thickness, thus B20>B10>B5 with corresponding lag time values of 4.5, 3 and 2.5 h, respectively. Selected B5 tablet formula exhibited a reasonable lag time after which the highest, complete % drug release at pH 6.8 was obtained. In addition, a good partitioning of valsartan, between the aqueous and organic phases in a ratio of 1:7, was observed. The selected formula was stable for at least 3 months under standard long-term and accelerated storage conditions. In conclusion, in vitro studies revealed that the novel time-clock system could be used successfully to deliver valsartan in a pulsatile pH-independent manner. It provided a desirable lag time followed by a rapid and complete drug release accompanied by an expected effective permeation through the biological membranes upon release in the duodenum; the window of absorption, as indicated by the two phase release study.     

双嘧达莫缓释微丸的研制及其体外释放特性

 目的：制备双嘧达莫pH非依赖型缓释微丸，使药物释放不受胃肠道pH值变化及个体差异的影响。方法：采用固体分散技术，将药物与联合载体（Eudragit L、EC和PEG 6000）的混和有机液喷包于微晶纤维素（MCC）空白丸芯上形成膜衣骨架型共沉淀物结构，以正交设计进行处方优化，考察不同pH条件下缓释微丸的释放特性。结果：缓释微丸的体外药物释放呈pH非依赖型释放特征，符合一级动力学方程。结论：具有溶解度pH依赖性的药物，以固体分散技术处理，通过不同性质载体的调节作用，可以制成pH非依赖型的缓释制剂。     

阿替洛尔非pH依赖型缓释片的制备及处方优化

以羟丙甲纤维素为缓释材料,琥珀酸为pH缓冲剂制备非pH依赖型阿替洛尔缓释片.考察以不同用量的羟丙甲纤维素和琥珀酸配制成不同处方缓释片,测定各个处方在0.1mol/L盐酸和pH7.4磷酸盐缓冲液中的释放度,采用多指标同步优化筛选处方.结果表明,优化处方在不同pH介质中均有较好的缓释效果.     

Extended release of flurbiprofen from tromethamine-buffered HPMC hydrophilic matrix tablets

Abstract

The pH-dependent solubility of a drug can lead to pH-dependent drug release from hydrophilic matrix tablets. Adding buffer salts to the formulation to attempt to mitigate this can impair matrix hydration and negatively impact drug release. An evaluation of the buffering of hydrophilic matrix tablets containing a pH-dependent solubility weak acid drug (flurbiprofen), identified as possessing a deleterious effect on hydroxypropyl methylcellulose (HPMC) solubility, swelling and gelation, with respect to drug dissolution and the characteristics of the hydrophilic matrix gel layer in the presence of tromethamine as a buffer was undertaken. The inclusion of tromethamine as an alkalizing agent afforded pH-independent flurbiprofen release from matrices based on both HPMC 2910 (E series) and 2208 (K series), while concomitantly decreasing the apparent critical effect on dissolution mediated by this drug with respect to the early pseudo-gel layer formation and functionality. Drug release profiles were unaffected by matrix pH-changes resulting from loss of tromethamine over time, suggesting that HPMC inhibited precipitation of drug from supersaturated solution in the hydrated matrix. We propose that facilitation of diffusion-based release of potentially deleterious drugs in hydrophilic matrices may be achieved through judicious selection of a buffering species.     

对乙酰氨基酚非pH依赖性缓释片的处方优化

目的:设计及优化非pH依赖性缓释片处方.方法:以对乙酰氨基酚为模型药物,设计不同配比的海藻酸钠和壳聚糖为混合骨架的缓释片处方,测定各处方在 0.1 mol·L-1盐酸和pH 6.8磷酸盐缓冲液中的释放度,采用多指标同步优化筛选处方.结果:优化的乙酰氨基酚缓释片处方含壳聚糖 85 mg、海藻酸钠 135 mg 时,呈现良好的体外非pH依赖性释放特征.结论:采用海藻酸钠和壳聚糖混合骨架易制得非pH依赖性缓释片,且方法简单、成本低,具有较高的实用价值.     

Physico-chemical characterization and in vitro/in vivo evaluation of loratadine:dimethyl-β-cyclodextrin inclusion complexes

A tricyclic, piperidine derivative of antihistamines, loratadine, which belongs in class II of the Biopharmaceutical Classification System, was investigated. It is an ionizable drug, whose solubility depends on the gastrointestinal pH, and the bioavailability is therefore very variable. Inclusion complexes were prepared by kneading method, containing loratadine (LOR) and dimethyl-β-cyclodextrin (DIMEB) in two different molar ratios in an attempt to achieve better dissolution and therefore the better bioavailability of loratadine. The formation and physicochemical properties of the inclusion complexes were investigated by means of dissolution tests, pH-dependent solubility studies, electrospray ionization mass spectrometry and diffusion-ordered 1H NMR spectroscopy. The in vivo efficiency of the complexes was examined in rat animal experiments to confirm the better in vitro dissolution. The instrumental examinations proved the presence of total complexes in 1:1 ratio in both compositions. However, the in vitro pH-dependent solubility results, the in vivo blood levels and the greater pharmacological effect prove that excess DIMEB is needed to achieve the pH-independent and complete solubility of LOR, and therefore better and more consistent bioavailability.     

人工神经网络多指标同步优化阿替洛尔非pH依赖型缓释片

目的：应用人工神经网络筛选阿替洛尔非pH依赖型缓释片的处方。方法：以羟丙甲纤维素为缓释材料,琥珀酸为pH缓冲剂研制非pH依赖型阿替洛尔缓释片,以不同用量的羟丙甲纤维素和琥珀酸配制成不同处方缓释片,测定各处方在pH7．4和0．1mol／L HCI中的释放度并计算得分,将此数据用于训练BP人工神经网络,并将此网络用于处方筛选。结果：优化处方在不同pH介质中均有较好的缓释效果。结论：人工神经网络多指标同步优化法可用于处方筛选。     

Development of a novel osmotically driven drug delivery system for weakly basic drugs

The drug substance SAG/ZK has a short biological half-life and because of its weakly basic nature a strong pH-dependent solubility was observed. The aim of this study was to develop a controlled release (cr) multiple unit pellet formulation for SAG/ZK with pH-independent drug release. Pellets with a drug load of 60% were prepared by extrusion/spheronization followed by cr-film coating with an extended release polyvinyl acetate/polyvinyl pyrrolidone dispersion (Kollidon SR 30 D). To overcome the problem of pH-dependent drug release the pellets were then coated with a second layer of an enteric methacrylic acid and ethyl acrylate copolymer (Kollicoat MAE 30 DP). To increase the drug release rates from the double layered cr-pellets different osmotically active ionic (sodium and potassium chloride) and nonionic (sucrose) additives were incorporated into the pellet core. Drug release studies were performed in media of different osmotic pressure to clarify the main release mechanism. Extended release coated pellets of SAG/ZK demonstrated pH-dependent drug release. Applying a second enteric coat on top of the extended release film coat failed in order to achieve pH-independent drug release. Already low enteric polymer levels on top of the extended release coated pellets decreased drug release rates at pH 1 drastically, thus resulting in a reversal of the pH-dependency (faster release at pH 6.8 than in 0.1N HCl). The addition of osmotically active ingredients (sodium and potassium chloride, and sucrose) increased the imbibing of aqueous fluids into the pellet cores thus providing a saturated drug solution inside the beads and increasing drug concentration gradients. In addition, for these pellets increased formation of pores and cracks in the polymer coating was observed. Hence drug release rates from double layered beads increased significantly. Therefore, pH-independent osmotically driven SAG/ZK release was achieved from pellets containing osmotically active ingredients and coated with an extended and enteric polymer. In contrast, with increasing osmotic pressure of the dissolution medium the in vitro drug release rates decreased significantly.     

pH modulation: a mechanism to obtain pH-independent drug release

Importance of the field: In formulation development, weakly acidic or basic drugs pose a major challenge as the solubility depends significantly on pH of the dissolution media. This gives rise to pH-dependent drug release, as the formulation is exposed to different pH ranges in the gastrointestinal tract. This indicates a need to carry out formulation optimization for such drugs while developing them into a dosage form.

Areas covered in this review: For overcoming pH-dependent behavior of drugs, pH-modifying excipients (which alter the microenvironment pH inside the formulation) are most commonly used. A combination of enteric and sustained release polymers can be used for weakly basic drugs. Other strategies include conversion of crystalline drug to amorphous form, enhancement of partitioning of unionized fraction of drug from the formulation, and using a combination of pH modifier and enteric polymer, micellar solubilization and inclusion complexation.

What the reader will gain: Readers will gain an insight into various formulation techniques for obtaining pH-independent drug release for weakly acidic and basic drugs.

Take home message: Readers will be able to evaluate the different formulation strategies in terms of their applicability and best use of the available strategies when designing their own research work for such drugs.