Improved dissolution and pharmacokinetic behavior of dipyridamole formulation with microenvironmental pH-modifier under hypochlorhydria

Microenvironmental pH Modification in Buccal/Sublingual Dosage Forms for Systemic Drug Delivery

Many drug candidates are poorly water-soluble. Microenvironmental pH (pH_M) modification in buccal/sublingual dosage forms has attracted increasing interest as a promising pharmaceutical strategy to enhance the oral mucosal absorption of drugs with pH-dependent solubility. Optimizing drug absorption at the oral mucosa using pH_M modification is considered to be a compromise between drug solubility and drug lipophilicity (Log D)/permeation. To create a desired pH_M around formulations during the dissolution process, a suitable amount of pH modifiers should be added in the formulations, and the appropriate methods of pH_M measurement are required. Despite pH_M modification having been demonstrated to be effective in enhancing the oral mucosal absorption of drugs, some potential risks, such as oral mucosal irritation and teeth erosion caused by the pH modifiers, should not been neglected during the formulation design process. This review aims to provide a short introduction to the pH_M modification concept in buccal/sublingual dosage forms, the properties of saliva related to pH_M modification, as well as suitable drug candidates and pH modifiers for pH_M modifying buccal/sublingual formulations. Additionally, the methods of pH_M measurement, pH_M modification methods and the corresponding challenges are summarized in the present review.

Development of an enhanced formulation to minimize pharmacokinetic variabilities of a weakly basic drug compound

Formulating poorly water soluble, weakly basic drugs with consistent exposure is often a challenge due to pH dependent solubility. When the oral formulation is exposed to different pH ranges in the gastrointestinal (GI) tract, drug precipitation or incomplete dissolution may occur resulting in decreased drug absorption and higher intra-and inter-patient pharmacokinetic variabilities.In the present study, a series of enhanced formulations containing organic acids and/or surfactants were developed and compared with conventional formulations with respect to their in vitro dissolution performance. The formulation containing 5% citric acid and 1% sodium lauryl sulfate (SLS) showed much less variations in dissolution performance at different pH conditions than a conventional formulation. The combination of citric acid and SLS demonstrated a synergistic effect as compared to use of citric acid alone or in combination with PEG4000 as a precipitation inhibitor.When compared with a conventional formulation and a spray-dried amorphous solid dispersion (ASD) formulation in a dog pharmacokinetics study, the enhanced formulation demonstrated the least AUC and C_max variability between the two gastric pH-controlled groups. In conclusion, an enhanced formulation using a combination of organic acid and surfactant is recommended for weakly basic drug compounds to minimize drug pharmacokinetic variabilities in clinical studies.

Enteric and hydrophilic polymers enhance dissolution and absorption of poorly soluble acidic drugs based on micro-environmental pH-modifying solid dispersion

The oral bioavailability of poorly water-soluble active pharmaceutical ingredient (API) is often inadequate for the desired therapeutic effect. Micro-environmental pH-modifying solid dispersion (micro pHm SD) is an effective method for enhancing the dissolution of pH-dependent soluble APIs. However, erratic bioavailability of these drugs was often found when the micro pHm SD of the drugs was orally administrated and passed through the gastrointestinal tract. Because the added alkalizer in micro pHm SD could be neutralized by the acid in the stomach, as a result not enough alkalizer is left to form alkaline micro-environment around the drug in the intestine, leading to poor dissolution and bioavailability of API. Enteric polymers are applicable materials for site-specific drug delivery that are insoluble in gastric tract but soluble in the intestine targeted for drug release. In this study, a poorly water-soluble model drug, toltrazuril (TOL), was prepared as enteric micro pHm SD with enteric, hydrophilic polymers and alkalizer. The surface of enteric micro pHm SD tablets staining and alkalizer protection test in the acid dissolution medium qualitatively and quantitatively confirmed the protective effects of the enteric polymer on the alkalizer. Dissolution studies revealed that the drug release from the enteric micro pHm SDs was improved significantly compared with micro pHm SD with no enteric polymer. The pH-dependent solubility of enteric polymer had effects on the dissolution of APIs from the SDs in neutral medium. Enteric micro pHm SDs with higher proportion of enteric polymer showed higher C_max and dissolution rate of TOL. The physicochemical characterization and the molecular interaction between drug and matrix were analyzed by electron microscopy (SEM), differential scanning calorimetry (DSC), and fourier transform infrared spectroscopy (FTIR), finding that the formation of hydrogen bonds between TOL and matrix was helpful to promote dissolution of TOL. Ca(OH)₂-TOL-PVPk30-HPMCAS 8: 8: 18: 6 was determined as the most optimal enteric micro pHm SD, which significantly improved the bioavailability of TOL and its active metabolism (TOLSO, TOLSO₂) in pharmacokinetic study and could effectively reduce the irritation of the gastrointestinal mucosa caused by the alkalizer Ca(OH)₂ when the SD was orally administrated to rabbits. The present study demonstrates that formulating APIs with poor water solubility as enteric micro pHm SD is an effective method for protecting the alkalizer in SD and improving the dissolution of APIs and the bioavailability following oral administration.

Effect of gastrointestinal transit on micro-environmental pH inside HPMC matrix tablets - in vitro study

A commonly used approach to enhance the dissolution of drugs with pH-dependent solubility is the incorporation of pH modifiers. The aim of this study was to evaluate the duration and extent of pH modifying effect on the micro-environmental pH in HPMC matrix by applying two mechanistic approaches regarding hydrodynamic stress on the tested formulation (i.e. static dissolution apparatuses (USP2) and dynamic approaches including the Advanced gastric simulator (AGS) and the Intestinal model for simulation of peristaltic action (IMSPA)). Moreover, the aim of our research was also the preparation of sustained-release matrix systems with improved - enhanced drug dissolution. In our study, the occurrence of a pH gradient in the gel layer of the HPMC tablets was observed during simulation of their passage along different compartments of the GIT. The pH gradient was affected by the media composition and duration of tablet exposure to the surrounding media. Both dissolution methods were also used to evaluate the influence of the mechanical stress on the drug release kinetics. Micro-environmental pH (pH_M) was evaluated, using two methods: the cryostatic method with a surface pH electrode, and with the incorporation of a pH sensitive dye (methyl orange) into the matrix tablets. Our study demonstrates a significantly higher dissolution rate due to mechanical stress during the bio-relevant simulation of GIT transit of the mechanically sensitive HPMC tablets with poorly soluble drugs. A considerably higher release rate was also observed from tablets with the weakly basic drugs dipyridamole and propranolol hydrochloride containing pH modifier in case of mechanically bio-relevant dissolution models compared to the USP2 apparatus. For the assessment of the pH_M, the incorporation of a pH indicator dye in the HPMC tablet proved to be more suitable, while the cryostatic method was found to be useful only for a rough pH_M estimation.

Enhanced pharmacokinetic performance of dapoxetine hydrochloride via the formulation of instantly-dissolving buccal films with acidic pH modifier and hydrophilic cyclodextrin: Factorial analysis, in vitro and in vivo assessment

Instantly dissolving buccal films have gained attention owing to their easy administration and capability to surmount the hepatic first pass effect of drugs. Dapoxetine hydrochloride (DPX) has a low oral bioavailability due to significant hepatic first pass metabolism. In addition, DPX is a weakly basic drug with a pH dependent solubility that could limit its dissolution in the body neutral fluids. In order to surpass these challenges, this work aimed at enhancing DPX bioavailability via the formulation of instantly dissolving buccal films comprising a pH modifier and a hydrophilic cyclodextrin. Tartaric acid and hydroxypropyl beta-cyclodextrin were selected as dual solubilizing agents based on the screening study. 3² factorial design was employed for the formulation and optimization of DPX films. Statistical analysis revealed that hydroxypropyl methyl cellulose E5: maltodextrin ratio and propylene glycol concentrations have significant effects on mechanical properties, percent DPX dissolved after 5 min, and in vivo mouth dissolving time at P  < 0.05. The optimized film [HPMC E5: MDX, 1:1 and 1% PG] showed no significant change of properties or drug dissolution upon storage at 40 °C/75% RH for a period of 3 months. In addition, the optimized film showed significantly enhanced absorption relative to the oral reference tablet. Therefore, the optimized film could be considered a promising delivery system for DPX with expected improved patient compliance and enhanced pharmacokinetic performance.

Formulation and Evaluation of a Novel Oral Oil-Based Suspension Using Micro-environmental pH-Modifying Solid Dispersion

Drugs with pH-dependent solubility that have poor water solubility can be identified in the drug discovery pipeline. Some of them have poor oral absorption, which can result in insufficient efficacy. Micro-environmental pH-modifying solid dispersion (micro pHm SD) is a promising approach to overcome the poor oral absorption of these drugs. In the present study, toltrazuril (TOL), a weakly acidic drug with poor aqueous and pH-dependent solubility, was used as a model drug. Using micro pHm SD, a novel oral oil-based suspension of TOL SD (TSDS) was developed, and the stability of this formulation was evaluated based on particle size, settling volume ratio, redispersibility, thermal stability, and drug content. The optimized soybean oil-based TSDS (S-TSDS) had high physicochemical stability and good histocompatibility with common inflammatory reactions. The results of the in vitro dissolution analysis showed that S-TSDS rapidly and markedly released the drug and provided higher efficacy and longer persistence against coccidiosis (above 90.9%) in rabbits. This technique could increase the oral absorption and bioavailability of new drug candidates.

Application of a Refined Developability Classification System

In 2010, the Developability Classification System was proposed as an extension of the Biopharmaceutics Classification System to align the classification system with the need for early evaluation of drug candidates according to their developability as oral formulations. Recent work on the Developability Classification System has resulted in the refined developability classification system (rDCS), consisting of standard investigations to estimate drug candidate solubility and permeability and offering customized investigations that are triggered when there is a potential for supersaturation/precipitation (e.g., salts of acids, weak bases) or to investigate permeation versus dissolution-limited absorption. In the present study, the rDCS concept was successfully applied to 6 marketed compounds (aciclovir, albendazole, danazol, dantrolene, dipyridamole, and piroxicam), for which there is a rich database of information. Furthermore, the rDCS was applied to 20 pipeline compounds from past and current research projects at Bayer AG. The rDCS was able to predict the results in humans correctly in 80% of cases. Overall, the results suggest that the rDCS is a highly useful tool for estimating the in vivo behavior of new drug candidates.

Amorphous solid dispersions of carvedilol along with pH-modifiers improved pharmacokinetic properties under hypochlorhydoria

Carvedilol (CAR) belongs to biopharmaceutics classification system class-II drugs, with poor aqueous solubility and pH-dependent solubility. The present study aimed to develop a novel amorphous solid dispersion (ASD) of CAR with acidic counter ions for pH modifications in microenvironment to improve the pharmacokinetic properties under hypochlorhydric conditions. CAR-ASD was prepared by freeze-drying in combination with counter ions and hydroxypropyl cellulose, and their physicochemical properties including dissolution behavior, storage stability, and photostability were characterized. Pharmacokinetic studies were carried out after oral administration of CAR samples in both normal and omeprazole-treated (30 mg/kg, p.o.) rats as a hypochlorhydria model. Among the tested six counter ions, citric acid (CA) was found to be a preferable pH-modifier of CAR with respect to the dissolution profile and photostability (both potency and colorimetric evaluation). In CAR-ASD formulation with 50% loading of CA (CAR-ASD/CA50), amorphization of CAR was observed during the preparation process. After the oral administration of crystalline CAR in rats under hypochlorhydric condition, there was a 34.4% reduction in the systemic exposure of CAR compared with that in normal rats. However, orally-dosed CAR-ASD/CA50 resulted in limited alterations of pharmacokinetic behavior between normal and omeprazole-treated rats. From these findings, addition of CA as pH-modifier in CAR-ASD might provide consistent pharmacokinetic behavior of CAR even under hypochlorhydric conditions.

Design and Evaluation of Hydrophilic Matrix System for pH-Independent Sustained Release of Weakly Acidic Poorly Soluble Drug

The aim of this research was to design and evaluate a hydrophilic matrix system for sustained release of glipizide, a weakly acidic poor soluble drug. A combination of inclusion complexation and microenvironmental pH modification techniques was utilized to improve the dissolution and pH-independent release of glipizide. Hydroxypropyl-β-cyclodextrin (HP-β-CD) was used as the complexation agent while sodium citrate and magnesium oxide (MgO) were used as model pH modifiers. The hydrophilic matrix tablets were prepared by powder direct compression and evaluated by in vitro dissolution study respectively in pH 6.8 and pH 1.2 dissolution media. The formulations containing MgO exhibited increased cumulative drug release from less than 40% in the reference formulation to 90% within 24 h in acidic media (pH 1.2). The release profile in acidic media was similar to the alkaline media (pH 6.8) with a similarity factor (f₂) of 55.0, suggesting the weakening of the effect of pH on the dissolution efficiency of glipizide. The release profile fitted well into the Higuchi model and the dominant mechanism of drug release was Fickian diffusion while case II transport/polymer relaxation occurred. In conclusion, combining inclusion complexation agents and pH modifiers had improved the dissolution of glipizide as well as achieved the pH-independent release profile.

Study of controlled-release floating tablets of dipyridamole using the dry-coated method

Dipyridamole (DIP), having a short biological half-life, has a narrow absorption window and is primarily absorbed in the stomach. So, the purpose of this study was to prepare controlled-release floating (CRF) tablets of dipyridamole by the dry-coated method. The influence of agents with different viscosity, hydroxypropylmethylcellulose (HPMC) and polyvinylpyrollidon K30 (PVP K30) in the core tablet and low-viscosity HPMC and PVP K30 in the coating layer on drug release, were investigated. Then, a study with a three-factor, three-level orthogonal experimental design was used to optimize the formulation of the CRF tablets. After data processing, the optimized formulation was found to be: 80 mg HPMC K4M in the core tablet, 80 mg HPMC E15 in core tablet and 40 mg PVP K30 in the coating layer. Moreover, an in vitro buoyancy study showed that the optimized formulation had an excellent floating ability and could immediately float without a lag time and this lasted more than 12 h. Furthermore, an in vivo gamma scintigraphic study showed that the gastric residence time of the CRF tablet was about 8 h.

Improved Dissolution of Dipyridamole with the Combination of pH-Modifier and Solid Dispersion Technology

The aim of this study was to develop a pH-independent release formulation of dipyridamole (DP) by the combined use of pH-modifier technology and solid dispersion (SD) technology employing enteric polymer, Eudragit^® S100 (Eud). Tartaric acid (TA) was selected as an appropriate pH-modifier in terms of improving the dissolution behavior of DP under neutral conditions. Upon optimization of the ratio of TA to DP, SD of DP with Eud and TA (SD-Eud/DP/TA) was prepared by a freeze-drying method. Scanning electron microscopic images revealed that DP was dispersed in the polymer in SD-Eud/DP/TA, and DP in SD-Eud/DP/TA was in an amorphous state, supported by powder X-ray diffraction and differential scanning calorimetry analyses. The dissolution behavior of SD-Eud/DP/TA was not dependent on the pH of the medium, although SD-Eud/DP exhibited very limited dissolution behavior under neutral conditions. Spectroscopic analysis suggested that there might be inter-molecular interaction among DP, TA and enteric polymer in SD-Eud/DP/TA, possibly leading to the stable pH-independent dissolution behavior of SD-Eud/DP/TA. TA in SD-Eud/DP/TA promoted the degradation of DP, suggesting that improving the stability of DP in SD-Eud/DP/TA might be key for its practical use. From these results, pH-independent dissolution behavior of SD-Eud/DP/TA could be achieved by an enteric polymer-based solid dispersion with a pH-modifier.

Effects of Manufacturing Methods on Dissolution and Absorption of Ketoconazole in the Presence of Organic Acid as a pH Modifier

Poorly water-soluble compounds have a potential risk of low and variable bioavailability caused by incomplete dissolution. Incorporation of organic acids as pH modifiers is effective method for solubility enhancement of basic compounds and requires no special technique and equipment. The purpose of this study was to evaluate the effect of manufacturing method on the extent of drug solubility enhancement. We successfully prepared the granules and tablets containing ketoconazole (KZ), which is weakly basic, as a model compound and citric acid as a pH modifier using conventional wet and dry granulations. KZ solubility under non-sink condition was enhanced with supersaturation using both wet and dry granulations. High-shear granulation was the most effective method in terms of KZ dissolution enhancement, because both an intimate contact and strong bonding between KZ and incorporated acid were achieved. KZ dissolved amount from the granules prepared by high-shear granulation was about eight times higher than that from the granules without the acid. The granulation involved to suppress a diffusion of acid dissolved, leading to the effectively maintained supersaturation state. The bioavailability of KZ after oral administration to rats was improved by applying high-shear granulation with citric acid independent of gastrointestinal pH. The granules prepared by high-shear granulation showed the bioavailability about 1.7-fold higher than that of the physical mixture in rats with and without neutralization of stomach. As a result, both the dissolution and absorption rates of KZ after oral administration were enhanced using conventional manufacturing technology.

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.

Management of experimental hypochlorhydria with iron deficiency by the composite extract of Fumaria vaillantii L. and Benincasa hispida T. in rat

The aim of the present study was to search the effective ratio of whole plant of Fumaria vaillantii Loisel (Fumaria vaillantii L.) and fruit of Benincasa hispida Thunb. (Benincasa hispida T.) in composite form, namely “FVBH” for the management of hypochlorhydria along with iron deficiency in male albino rats. Hypochlorhydria refers to suppression of hydrochloric acid secretion by the stomach. Hypochlorhydria was induced by ranitidine in this study. We used four composite extracts of the mentioned plant and fruit with different ratios (1:1, 1:2, 2:1, and 3:2) for searching the most effective composite extract for the correction of hypochlorhydria. Gastric acidity is an important factor for iron absorption. Thus, hypochlorhydria causes iron deficiency in rat and it was prevented significantly by the extract treatment at the ratio of 1:1 of the said plant and fruit. The correction of iron deficiency by the composite extract was compared with iron supplementation to hypochlorhydric rat. It was found that preadministration followed by coadministration of FVBH-1 (1:1) able to prevent the ranitidine-induced hypochlorhydria and iron deficiency. The composite extract, FVBH-1 (1:1) significantly (P<0.05) increased the pepsin concentration, chloride level in gastric juice, iron levels in serum and liver along with blood hemoglobin level than other ratios used here. Hence, it can be concluded that FVBH-1 (1:1) is an effective herbal formulation for the management of hypochlorhydria and related iron deficiency.

[Strategic formulation study on dry powder inhalation system based on modulated molecular properties and controlled pharmacokinetics]

Cyclosporine A (CsA) has been widely used as an immunosuppressive agent, and recent outcomes from clinical studies are indicative of the potent therapeutic potential of CsA for chronic asthma and airway inflammation. The clinical use of CsA for airway inflammatory diseases is partly limited because of low oral bioavailability and severe systemic side effects. A number of CsA dosage forms have been proposed to overcome these drawbacks, for example, nebulizer formulation and metered-dose inhaler formulation for inhalation therapy, whereas these liquid formulations sometimes contain organic solvents and other solubilizers, leading to local irritant potency. In this context, our group developed a dry powder inhalation (DPI) system of CsA, employing a polymer-based amorphous solid dispersion (ASD) approach, for inhalation therapy on airway inflammations. There was marked improvement in dissolution behavior of the ASD formulation compared with that of an amorphous CsA. The new DPI system of CsA exhibited high dispersibility and suitable particle distribution for inhalation therapy. In vivo experiments demonstrated that inhaled DPI system of CsA attenuated inflammatory events in experimental asthma/chronic obstructive pulmonary disease (COPD) model rats as evidenced by a decrease of infiltrated granulocytes, and there was no excessive increase in systemic exposure of CsA at a pharmacologically effective dose, possibly leading to reduced systemic side effects. From these findings, combination use of CsA-loaded ASD and DPI systems might be a promising approach for the treatment of airway inflammatory diseases with improved pharmacodynamics and lower systemic exposure.