pH-independent Drug Release Research Articles

Effect of Omeprazole Administration on the Pharmacokinetics of Oral Extended-Release Nifedipine in Healthy Subjects.

Oral extended-release (ER) dosage forms have been used to sustain blood drug levels, reduce adverse events, and improve patient compliance. We investigated potential effects of comedication on pharmacokinetic exposure of nifedipine ER products with different formulation designs and manufacturing processes. A clinical study compared a generic version of nifedipine ER tablet with pH-dependent dissolution behavior with an osmotic pump product with pH independent drug release under fasting condition. In this study, two nifedipine tablet products were tested with or without short-term omeprazole comedication in healthy subjects. Seven-day administration of omeprazole before nifedipine dosing significantly increased the gastric pH, and subsequently increased the geometric least square (LS) means of area under the concentration-time curve from time zero to the last measurable timepoint (AUC0-t ) and maximum plasma concentration (Cmax ) of nifedipine to 132.6% (90% confidence interval (CI): 120.6-145.7%) and 112.8% (90% CI: 100.8-126.3%) for pH-dependent ER tablets, and 120.6% (90% CI: 109.7-132.5%) and 122.5% (90% CI: 113.7-131.9%) for the pH-independent ER tablets, respectively. Similar extent of increase in AUC0-t and Cmax was confirmed in the subpopulations whose gastric pH was ≥ 4 or ≤ 3 in subjects with or without omeprazole administration. Given that similar increases in drug exposures were observed for both pH-dependent and pH-independent nifedipine formulations and the geometric LS mean ratios were between 112% and 133% with and without short-term omeprazole comedication, the gastric pH may have limited effects on omeprazole-induced nifedipine PK changes on the tested formulations. The inhibition of cytochrome P450 3A4 activity may play a significant role causing nifedipine exposure changes for both formulations, which would warrant additional assessment.

Hydrodynamically Balanced Capsule of Famotidine: An Improved Delivery via Gastroretentive Hydrogels

Objective: The aim of the present study was to increase the absolute bioavailability of famotidine, enhanced patient compliance in the treatment of peptic ulcer by increasing its gastric residence time and controlled local release of drug upto 12 hours. Materials and Methods: Hydrodynamically balanced capsules of famotidine were prepared, consisting of floating matrix granules, which formed hydrogels. Effects of different formulation variables namely hypromellose (HPMC 4000 cps, HPMC 5600 cps, HPMC 15000 cps), effervescent agent (potassium bicarbonate) and mixing time were studied. Optimization study included 23 full factorial design with t50% and t80% as the kinetic parameters (response variable). Matrix characterization included scanning electron microscopy. All prepared formulations were evaluated to various parameters such as micromeritics properties, % buoyancy and in vitro drug release studies. Results and Discussion: The optimized formulation (F4) remains buoyant for more than 12 hrs. The in-vitro drug release study indicated that increasing the viscosity of HPMC resulted in sustained drug release with long floating duration. SEM studies showed definite entrapment of the drug in the matrix and hydrogel formation. Results showed a pH independent but polymer viscosity dependent drug release profile. The release kinetics followed Higuchi model and mechanism of release was found to be non-Fickian diffusion. Conclusion: Famotidine-loaded hydrodynamically balanced capsules were successfully prepared and prove to be useful for prolonged gastric residence of the drug, better bioavailability, patient compliance and improve delivery for enhanced anti-ulcer activity.

Modular solid dosage form design – Application to pH-independent release of a weak-base API

A novel approach to solid dosage form design is investigated, whereby instead of blending the ingredients and subsequently compacting the mixture, the dosage form is made by assembling prefabricated components, each with a specific function. The approach was used to formulate a weak-base API (active pharmaceutical ingredient), such that the modular dosage forms exhibited pH-independent drug release. Tablet-like dosage forms of ciprofloxacin (CPR), used as model weak-base drug, were prepared in order to generate dosage forms exhibiting pH-independent drug release. The dosage forms were made by assembling two types of prefabricated modules onto 3D stacks. The modules were hydroxypropyl methylcellulose circular film wafers, loaded with either CPR or citric acid (CA). CA-wafers served the function of pH-modifier modules in the microenvironment of the dosage form during the dissolution process. In vitro drug release from dosage forms consisting of CA- and CPR-wafers stacked in alternate sequence was compared with the release from assemblies containing CPR-wafers only, under pH = 1.2 and pH = 6.8 conditions. In the absence of CA-wafers, CPR release was ~25-fold slower at pH = 6.8 compared to pH = 1.2. Inclusion of CA-wafers in the dosage form assembly accelerated and decelerated drug release at pH = 6.8 and pH = 1.2, respectively, which resulted in overlapping drug release profiles under the two pH conditions. The two drug release profiles met the criteria for sameness as assessed by the f1 (difference) and f2 (similarity) factors. Modeling of drug release kinetics pointed toward polymer erosion as the primary mechanism of drug release for the overlapping pH = 1.2 and pH = 6.8 profiles. In terms of their drug release properties, the multi-modular dosage form assemblies exhibited the attributes and behavior of single bodies, rather than the combined contributions from multiple individually-operating modules. The initial geometry of the dosage form, characterized by the surface area (SA), volume (V) and SA/V ratio accounted for drug release kinetics in the same fashion as for traditional tablet compacts.

Fabrication, optimisation and in vitro evaluation of docetaxel and curcumin Co-loaded nanostructured lipid carriers for improved antitumor activity against non-small cell lung carcinoma

Aim To develop docetaxel (DT) and curcumin (CUR) co-loaded nanostructured lipid carriers (DTCR-NLCs) for ratiometric co-targeting to non-small cell lung carcinoma (NSCLC) cells. Methods The DTCR-NLCs were developed by employing a high-pressure homogenisation technique and optimised by employing a rotatable central composite design response surface methodology (RCCD-RSM) via the design of experiments (DoE) approach. Results The optimised DTCR-NLCs had a particle size (D90) of 150.2 ± 5.2 nm, Pdi of 0.263 ± 0.15, zeta potential of +26.3 ± 5.2 mv. The % drug loading (% DL) of DT and CUR was observed to be 1.38 ± 0.98 and 2.99 ± 1.24, respectively. Dissolution studies depicted a pH-independent drug release (≈98% drug release at 144 h). The DTCR-NLCs were stable and haemocompatible. MTT cell viability assay of DTCR-NLCs demonstrated considerably increased cytotoxicity towards NCI-H460 cells. Conclusions The developed DTCR-NLCs heralds the future of an efficacious and safer Taxane therapy for NSCLC.

Sustained release dosage form of noscapine HCl using hot melt extrusion (HME) technique: formulation and pharmacokinetics.

Sustained release formulation of noscapine (Nos) HCl could be useful in maintaining plasma Nos HCl level for prolonged period of time, which is important for chemo-sensitization. However, weakly basic drugs like Nos HCl have pH-dependent solubility. Therefore, the purpose of this study was to achieve pH-independent drug release by developing the sustained release dosage form of Nos HCl using biodegradable polymer Eudragit RLPO and FDA-approved pH modifier citric acid (CA) by hot melt extrusion (HME) technique. Nos HCl was successfully formulated using 10% CA with 91.2 ± 1.34% drug recovery through the extruder. X-ray diffraction (XRD) results showed that drug was completely dispersed in the polymer and changed to amorphous from its crystalline form. In vitro drug release studies in pH 6.8 buffershowed that formulation containing 10% CA released 70.99 ± 3.85% drug in 24h after initial burst release of 40.04 ± 2.39% compared toformulation without CA. Furthermore, in vivo pharmacokinetic data showed the sustained release plasma concentration time curve with significant (p < 0.05) increase in area under curve (AUC) in NosHCl extrudate compared toNos HCl solution. Overall, HME can be used to enhance the bioavailability and achieve the pH-independent solubility of weakly basic drugs like Nos HCl. Graphical abstract.

Development and In Vitro-In Vivo Evaluation of a Novel Sustained-Release Loxoprofen Pellet with Double Coating Layer.

This study aimed to develop a novel sustained release pellet of loxoprofen sodium (LXP) by coating a dissolution-rate controlling sub-layer containing hydroxypropyl methyl cellulose (HPMC) and citric acid, and a second diffusion-rate controlling layer containing aqueous dispersion of ethyl cellulose (ADEC) on the surface of a LXP conventional pellet, and to compare its performance in vivo with an immediate release tablet (Loxinon®). A three-level, three-factor Box-Behnken design and the response surface model (RSM) were used to investigate and optimize the effects of the citric acid content in the sub-layer, the sub-layer coating level, and the outer ADEC coating level on the in vitro release profiles of LXP sustained release pellets. The pharmacokinetic studies of the optimal sustained release pellets were performed in fasted beagle dogs using an immediate release tablet as a reference. The results illustrated that both the citric acid (CA) and ADEC as the dissolution- and diffusion-rate controlling materials significantly decreased the drug release rate. The optimal formulation showed a pH-independent drug release in media at pH above 4.5 and a slightly slow release in acid medium. The pharmacokinetic studies revealed that a more stable and prolonged plasma drug concentration profile of the optimal pellets was achieved, with a relative bioavaibility of 87.16% compared with the conventional tablets. This article provided a novel concept of two-step control of the release rate of LXP, which showed a sustained release both in vitro and in vivo.

Development of pH Independent Drug Release System for Dipyridamole

Abstract: Introduction: Dipyridamole is an Anti-platelet agent exhibits release problems at higher pH of small intestine due to its pH dependent solubility and precipitation followed by interruption of drug release from dosage form. To overcome this extended release formulation was developed by using pH modulating agent (tartaric acid). Objective: Present study was undertaken with a view of the formulations evaluated by performing dissolution testing on developed extended released tablets. Method: development of dissolution method at different time points and USP Apparatus 1 (basket) and 2 (paddle) at rotating speeds of 50 or 100 rpm used to evaluate the release characteristics of the formulations. Furthermore, solubility and in vitro dissolution studies of formulated tablets were performed at pH values of 1.2 and 5.5. Results: In this study we found increasing volume of dissolution medium pH 5.5 phosphate buffers drug precipitation is increased. The developed dissolution method was validated according to ICH guidelines for various parameters such as specificity, accuracy, precision, and stability. The dissolution method was confirmed by determining the dissolution rate of extended released Dipyridamole tablets containing pH modulating agent. The best in vitro dissolution profile was obtained using pH 5.5 phosphate buffer as the dissolution medium (500 ml) stirred at 100 rpm. A comparison of the dissolution profiles in official and developed media showed significant differences based on f1 and f2 values. Conclusoni: The developed dissolution test exhibited a higher capacity than the compendia methods in differentiating the release profiles of pH independent extended release tablets. It can be applied during formulation development and quality control analysis of pH independent extended release tablets for evaluation of the effects of pH modifier in dissolution medium and processing parameters. Key words: Tartaric acid, Dissolution media, Extended release Dipyridamole Tablets.

A Biopredictive In Vitro Comparison of Oral Locally Acting Mesalazine Formulations by a Novel Dissolution Model for Assessing Intraluminal Drug Release in Individual Subjects

Drug release and availability at the site of action are the major factors determining the clinical response for locally-acting gastrointestinal (GI) drug products. The present work focused on the prediction of site and extent of in vivo mesalazine release after oral administration to a variety of subjects using individualized in vitro drug release experiments. First, experiments mimicking GI passages in average adult subjects were performed. Then, results from a study screening fasted in vivo pH and transit profiles in individual subjects were translated into a novel in vitro dissolution model enabling to mimic individual GI pH-profiles and transit times with physiologically relevant dissolution media. A selection of monolithic and multiparticulate mesalazine formulations with pH-dependent and pH-independent drug release was screened with the novel dissolution model. Results of the study indicate that dosage form performance can be significantly different in individual subjects and highlight the importance of addressing individual physiological parameters relevant to intraluminal drug release when the aim is to predict the in vivo performance of locally-acting mesalazine formulations in individual patients. The novel in vitro dissolution approach thus represents a valuable tool for both improving individual oral therapy with locally-acting GI drug products and assessing bioequivalence of these formulations.

Alginate-polyvinyl alcohol based interpenetrating polymer network for prolonged drug therapy, Optimization and in-vitro characterization

A new natural and synthetic polymeric blend to form interpenetrating polymer network (IPN) hydrogels was synthesized utilizing sodium alginate and PVA as polymers by free radical polymerization employing 2-Acylamido-2-methylpropane-sulfonic acid as monomer (AMPS) and tramadol HCl as model drug through 32 level full factorial design to evaluate the impact of selected independent factors i.e. polymer (sodium alginate) and monomer (AMPS) contents on swelling index at 18th hour, percent drug release at 18th hour, time required for 80% drug release and drug entrapment efficiency as dependent variables. FTIR, SEM, sol-gel analysis, equilibrium swelling studies and in-vitro release kinetics were performedfor in-vitro characterization of formulated IPN hydrogels. In-vitro studies carried out at pH 1.2 and pH 7.4 revealed pH independent swelling and drug release from polymeric IPN, providing controlled drug release for an extended period of time with improved entrapment efficiency, thereby concluding that this polymeric blend may be a promising system for the prolonged drug delivery.

DESIGN AND DEVELOPMENT OF A NOVEL PH INDEPENDENT CONTROLLED RELEASE

Ondansetron HCl is a widely used drug in the treatment of chemotherapy induced nausea and vomiting; post operative nausea and vomiting. It is a weakly basic drug with pH dependent drug release. The drug is practically highly ionised in acidic pH (1.2), precipitated in higher pH of small intestine. Hence, in the present study, it was tried to achieve pH-independent drug release. We adopted a very simple technique formulation containing two different polymers such as an anionic (sodium alginate) and nonionic (HPMCK100). It was found that the formulation F8 (intra and extra granulation technique) showed good correlation drug release in both SGF pH 1.2 and pH 6.8 phosphate buffer.

Development of pH-Independent Drug Release Formulation Using Lipocalin-Type Prostaglandin D Synthase

The purpose of this study was to develop a pH-independent drug release formulation using lipocalin-type prostaglandin D synthase, a member of the lipocalin superfamily, with the function of forming complexes together with various small lipophilic molecules. Dipyridamole, a poorly water-soluble drug, showing a pH-dependent solubility profile, was used as the model drug. The solubilization of dipyridamole was achieved by a simple complex formulation method with lipocalin-type prostaglandin D synthase. The complex formulation was produced successfully by spray drying, and the obtained powder formulation showed complete dissolution in fasted-state simulated gastric fluid (pH, 1.6) and phosphate-buffered solution (pH, 6.8). In addition, the potential stability of the complex formulation was assessed, and the dissolution profile of the produced powder at pH 6.8 was maintained after 4-week storage under several storage conditions. Furthermore, a pharmacokinetic study using hypochlorhydria model rats was performed to verify the improvement of the intestinal absorption behavior, and eventually the complex formulation overcame the problematic absorption profile of dipyridamole in the elevated gastric pH conditions. These results, taken together, demonstrate that the use of this well-designed drug-delivery carrier is feasible for the development of pH-independent drug release formulations.

Modulation of pH-Independent Release of a Class ΙΙ Drug (Domperidone) from a Polymeric Matrix Using Acidic Excipients

Drug release from polymeric matrix systems is the rate-limiting step for drug bioavailability and is determined by drug solubility; most drugs show pH-dependent solubility. Polymeric matrices remain in the gastrointestinal tract for a longer period of time and are exposed to environments of varying pH, which can adversely affect drug release. In the present study, the pH-independent drug release of domperidone was achieved by modifying the microenvironmental pH of a swollen polymeric matrix using acidic excipients (citric acid and tartaric acid). Matrices were prepared by a water-based, wet-granulation technique and evaluated for various official and unofficial parameters. In vitro drug release was studied using USP dissolution apparatus and pH 6.80 phosphate buffer as dissolution medium. Release kinetics was evaluated according to various mathematical models. Results show that domperidone release can be effectively modified by inclusion of acidic excipients in the formulations. Acidic excipients modulated microenvironmental pH and avoided the effect of dissolution medium pH on drug release. The resultant formulations are easy to prepare and scale up for commercial manufacturing. Better pH-independent release, following zero-order kinetics, was achieved with tartaric acid.

Pectin/anhydrous dibasic calcium phosphate matrix tablets for in vitro controlled release of water-soluble drug

Different pectin/anhydrous dibasic calcium phosphate (ADCP) matrix tablets have been developed in order to obtain controlled release of a water-soluble drug (theophylline). Swelling, buoyancy and dissolution studies have been carried out in different aqueous media (demineralized water, progressive pH medium, simulated gastric fluid, simulated intestinal fluid and simulated colonic fluid), to characterize the matrix tablets. When the pectin/ADCP ratio was ≥0.26 (P1, P2, P3 and P4 tablets) a continuous swelling and low theophylline dissolution rate from the matrices were observed. So, pectin gel forming feature predominated over the ADCP properties, yielding pH-independent drug release behavior from these matrices. On the contrary, pectin/ADCP ratios ≤0.11 (P5 and P6 tablets) allowed to achieve drug dissolution pH dependent. Consequently, the suitable selection of the pectin/ADCP ratio will allow to tailor matrix tablets for controlled release of water-soluble drugs in a specific manner in the gastrointestinal tract.

Development and Optimization of Venlafaxine Hydrochloride Sustained Release Triple Layer Tablets Adopting Quality by Design Approach

Purpose:Venlafaxine hydrochloride sustained release formulation increases patient compliance by reducing frequency of administration and it also reduces side effects like nausea and vomiting. Hence the objective of present investigation was to develop triple layer sustained release tablets of venlafaxine HCl using xanthan gum or polyethylene oxide. Methods:The venlafaxine HCl 150 mg sustained release tablets were prepared by wet granulation technique where drug was incorporated in middle layer with part of polymer. The barrier layers were composed of remaining polymer and other excipients. The granules and tablets were characterised. Optimized batches were also tested for drug release at different pH and in presence of ethanol, for kinetics of drug release and for water uptake/swelling. Results: Preliminary trials of monolayer tablet showed burst release due to high dose and solubility of venlafaxine HCl and hence triple layer tablets were developed. Granules of middle layer exhibited good flow properties. The comparative drug release to Effexor? XR capsule 150 mg could be achieved by modulating the concentration of polymer and diluents in middle layer as well as in barrier layers. Higher amount of polyethylene oxide was required as compared to xanthan gum which may be due to high water uptake and poor gel strength of polyethylene oxide. The optimized formulations showed pH independent drug release as well as ethanol had no effect on drug release. Effexor? XR capsule and optimized batches followed Weibull kinetics for drug release. The radar diagrams showed the comparable drug release to innovator in both the optimized formulations but point to point correlation was observed in batch with xanthan gum. Conclusion: The layered matrix tablets formulated successfully using hydrophilic polymers, xanthan gum or polyethylene oxide, to sustain the release of highly soluble drug like venlafaxine HCl.

Evaluation of hydrophilic matrix tablets based on Carbopol® 971P and low-viscosity sodium alginate for pH-independent controlled drug release

Background: The aim of this study was to evaluate matrix tablets containing different ratios of Carbopol® 971P (CP) to low-viscosity sodium alginate (SA) and assess their suitability for pH-independent controlled drug release. Methods: Two processing methods (physical mixing, PM and spray-drying, SD) were applied before compaction and the release from corresponding matrices was compared. The release from CP-SA PM matrices was also investigated using three model drugs (paracetamol, salicylic acid, and verapamil HCl) and two dissolution media (0.1 N HCl or phosphate buffer, pH = 6.8), and the release rate, mechanism, and pH-dependence were characterized by fitting of Higuchi and Peppas models, and evaluation of similarity factor. Furthermore, swelling behavior of CP-SA matrix tablets was studied for evaluating its impact on drug release. Results: The processing method (SD or PM) markedly affected the drug release from CP-SA matrices. ANOVA tests showed significant effects of the CP:SA ratio and drug type on the release rate (expressed by the constant, KH, from Higuchi model) and of the dissolution medium on the release mechanism (expressed by the exponent, n, from Peppas model). Similarity factor (f2) indicated that the CP:SA ratios ≥ 25:75 and ≥ 50:50 were suitable for pH-independent release of paracetamol and salicylic acid, respectively, although for verapamil HCl, the matrix with low CP:SA ratio (0:100) showed remarkably reduced pH-dependence of release. Swelling parameters (water uptake and mass loss) were significantly changed with experimental variables (CP:SA ratio, medium, and time) and were in good correlation with drug release. Conclusion: Matrix tablets based on CP and SA form a potentially useful versatile system for pH-independent controlled drug release.

Controlled release reservoir mini tablets approach for controlling the drug release of Galantamine Hydrobromide

The objective of this study is to explore and investigate the reservoir mini tablets approach to control the release of Galantamine Hydrobromide in comparison to desired release profile to the Innovator formulation Razadyne® ER capsules as disclosed in US Patent 7,160,559 which is granted to Janseen Pharmaceutica NV. The core mini tablets were prepared using the direct compression and wet granulation methods. These core mini tablets were further coated with Galantamine Hydrobromide in two different portions; 70% as controlled release and 30% as immediate release and then filled in empty hard gelatin capsule shells. The dissolution profiles of each formulation were compared to those of Razadyne® ER capsules and the mean dissolution time (MDT), dissolution efficiency (DE%) and dissolution similarity (f2 factor) were calculated. It was observed that core formulation plays an important role in controlling the drug release as well as maintaining pH independent drug release profile. The release mechanism of GAH from reservoir mini tablet formulation follows Higuchi and first order. These results imply that controlled release reservoir mini tablets which further filled into empty hard gelatin capsule shells can be a suitable method to formulate controlled release Galantamine hydrobromide.

Formulation and development of release modulated colon targeted system of meloxicam for potential application in the prophylaxis of colorectal cancer

The objective of the present study was to develop a colon targeted system of meloxicam for potential application in the prophylaxis of colorectal cancer. Efficacy of selective cyclooxygenase–2 inhibitors has been proven in colorectal cancer. Meloxicam is a selective cyclooxygenase–2 inhibitor with pH-dependent solubility. To achieve pH-independent drug release of meloxicam, pH modifying agents (buffering agents) were used. Meloxicam tablets containing polyethylene oxide were dually coated with ethyl cellulose containing hydrophilic material, polyethylene glycol as an inner coating layer and methyl acrylate, methyl methacrylate, and methacrylic acid copolymer (Eudragit® FS 30D) as outer coating layer for colon targeting. Optimized tablet formulations demonstrated good potential to deliver the drug to the colon by successfully exhibiting a lag time of 5 h during in vitro drug release study. An in vivo evaluation study conducted to ascertain pharmacokinetic parameters in rabbits revealed that the onset of drug absorption from the coated tablets (Tlag time = 4.67 ± 0.58 h) was significantly delayed compared to that from the uncoated tablets. The AUC0→t and AUC0→∞ for coated tablets were lower than of uncoated tablets, although the difference was not significant (p > 0.01). The roentgenography study revealed that the tablet remained intact, until it reached the colon (5 h), which demonstrates that the system can efficiently deliver the drug to the colon. This study demonstrated that a meloxicam-loaded colon targeted system exhibited promising targeting and hence may be used for prophylaxis of colorectal cancer.

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.

Development and investigation of gastro retentive dosage form of weakly basic drug

The release of drug substance from controlled-release dosage forms is often pH-dependent since most drugs are either weak acids or weak bases. A system that permits the drug release to be changed freely while maintaining pH-independent drug release (model drug was Domperidone) was developed. Powder mixture of drug and HPMC K4M, eudragit L100, sodium bicarbonate (as gas-generating agent) and other excipients were mixed and directly compressed using single-punch tablet compression machine. It was found that sodium bicarbonate reacts with HCl and produce carbon dioxide which creates pores in tablet and elevates swelling by wetting the polymer. So it helps in maintaining the buoyancy. The release rate could be modified by varying the polymer ratio. The prepared tablets were evaluated for general appearance, content uniformity, hardness, friability, buoyancy, in vitro drug release and in vivo studies.The best formulation (D1) was selected based on in vitro characteristics and was used in vivo radiographic studies by incorporating BaSO4. These studies revealed that the tablets remained in the stomach for 250630 min in fasted rabbits and indicated that gastric retention time was increased by the floating principle, which was considered desirable for the absorption window drugs. The linear regression analysis and model fitting showed that all these formulations followed Higuchi model, which had a higher value of correlation coefficient(r). The scanning electron microscopy images of the tablet (D1 formulation) were taken before and after dissolution and images showed that the drug was released from matrix by diffusion mechanism. Stability studies of all formulations were carried out at elevated temperature and humidity conditions of 4062oC/7565% RH and a control sample was placed at an ambient condition for 12 months. It was found that there was no significant change in buoyancy property as well as in drug content from initial drug content of all the formulations at the end of 12 months, indicating that the formulations are stable.

Strategies to Overcome pH-Dependent Solubility of Weakly Basic Drugs by Using Different Types of Alginates

Weakly basic drugs demonstrate higher solubility at lower pH, thus often leading to faster drug release at lower pH. The objective of this study was to achieve pH-independent release of weakly basic drugs from extended release formulations based on the naturally occurring polymer sodium alginate. Three approaches to overcome the pH-dependent solubility of the weakly basic model drug verapamil hydrochloride were investigated. First, matrix tablets were prepared by direct compression of drug substance with different types of sodium alginate only. Second, pH-modifiers were added to the drug/alginate matrix systems. Third, press-coated tablets consisting of an inner pH-modifier tablet core and an outer drug/sodium alginate coat were prepared. pH-Independent drug release was achieved from matrix tablets consisting of selected alginates and drug substance only. Alginates are better soluble at higher pH. Therefore, they are able to compensate the poor solubility of weakly basic drugs at higher pH as the matrix of the tablets dissolves faster. This approach was successful when using alginates that demonstrated fast hydration and erosion at higher pH. The approach failed for alginates with less-pronounced erosion at higher pH. The addition of fumaric acid to drug/alginate-based matrix systems decreased the microenvironmental pH within the tablets thus increasing the solubility of the weakly basic drug at higher pH. Therefore, pH-independent drug release was achieved irrespective of the type of alginate used. Drug release from press-coated tablets did not provide any further advantages as compound release remained pH-dependent.