Effect of gastric residence time on the oral absorption of rebamipide sustained-release tablets in beagle dogs

Drug Nanocrystals in Oral Absorption: Factors That Influence Pharmacokinetics

Despite the safety and convenience of oral administration, poorly water-soluble drugs compromise absorption and bioavailability. These drugs can exhibit low dissolution rates, variability between fed and fasted states, difficulty permeating the mucus layer, and P-glycoprotein efflux. Drug nanocrystals offer a promising strategy to address these challenges. This review focuses on the opportunities to develop orally administered nanocrystals based on pharmacokinetic outcomes. The impacts of the drug particle size, morphology, dissolution rate, crystalline state on oral bioavailability are discussed. The potential of the improved dissolution rate to eliminate food effects during absorption is also addressed. This review also explores whether permeation or dissolution drives nanocrystal absorption. Additionally, it addresses the functional roles of stabilizers. Drug nanocrystals may result in prolonged concentrations in the bloodstream in some cases. Therefore, nanocrystals represent a promising strategy to overcome the challenges of poorly water-soluble drugs, thus encouraging further investigation into unclear mechanisms during oral administration.

Design and evaluation of in vivo bioavailability in beagle dogs of bilayer tablet consisting of immediate release nanosuspension and sustained release layers of rebamipide

The purpose of this study was to develop a once-daily, bilayer matrix tablet with immediate (IR) and sustained release (SR) layers of poorly water-soluble and absorption site dependent rebamipide (RBM) to substitute three times a day IR tablet. Owing to the pH-dependent poor water solubility of RBM in low pH condition, salt-caged nanosuspensions (NSPs) consisting of RBM and poloxamer 407 (POX 407) or poloxamer 188 (POX 188) were prepared using an acid-base neutralization method to increase the dissolution rate, which was subsequently applied to the immediate-release (IR) layer. Polyethylene oxide (PEO) with different molecular weights (PEO 100,000 and PEO 5,000,000) and hydroxypropyl methylcellulose 4000 (HPMC 4000) were then investigated as SR agents to incorporate into the SR layer with pure RBM via wet granulation method. The dissolution profile of the optimized bilayer tablet having 50% IR and 50% SR layer of 300 mg RBM showed that the IR layer could rapidly disintegrate in pH 1.2 buffer solution within 2 h, reaching 50% of drug release from the tablet, followed by an extended drug release from the SR layer in pH 6.8 buffer over 24 h. An in vivo pharmacokinetic study was carried out in beagle dogs to compare the optimal formulation (300 mg RBM bilayer tablet) and the commercial tablet (Mucosta® 100 mg) as a reference. Unexpectedly, despite enhanced dissolution rate in a controlled manner, a designed bilayer tablet had no dose- and dosage form dependent in vivo bioavailability in beagle dogs as compared with IR 100 mg RBM reference tablet. It was evident that solubility in low pH condition, gastric residence time and absorption site of RBM should be carefully considered for designing specific SR or gastroretentive dosage form to improve therapeutic outcomes.

Electrostatic molecular effect of differently charged surfactants on the solubilization capacity and physicochemical properties of salt-caged nanosuspensions containing pH-dependent and poorly water-soluble rebamipide

In this study, the electrostatic molecular effect of differently charged surfactants on the solubilization capacity and physicochemical properties of salt-caged nanosuspensions (NSPs) containing poorly water-soluble drug was investigated. Anionic rebamipide (RBM) was chosen as a model drug because of its poor water solubility in low pH condition and ionizable acidic forms. Negatively charged sodium lauryl sulfate (SLS) and positively charged cetyltrimethylammonium bromide (CTAB) were selected as surfactants for the preparation of NSPs or in the dissolution medium. Salt-caged NSPs surrounded by NaCl were prepared by the HCl-NaOH neutralization method in the presence of poloxamer 407. Interestingly, the addition of positively charged CTAB in the preparation process or the dissolution media could interfere with the solubilization capacity of salt-caged NSPs containing a negatively charged drug via intermolecular electrostatic attraction. In the presence of positively charged CTAB, the salt-caged NSP was disordered in structure via electrostatic attractive interaction with partially ionizable anionic RBM resulting in changes in the physicochemical properties of the salt-caged NSP such as low drug content, increased particle size, decreased dissolution rate, and the formation of water-insoluble precipitates with rough and irregular crystals. This inhibitory effect of CTAB on the dissolution rate of pure RBM and the salt-caged NSP in pH 6.8 intestinal fluid was pronounced in a concentration-dependent manner mainly owing to the formation of precipitates, so-called poorly soluble complexes. When the salt-caged NSP (F1) was dissolved in DW containing CTAB, the dissolution rate decreased more significantly, dissolving less than 20% within 2 h. Depending on the surfactant charges, the charge density and the initial potential were varied during the dissolution of NSPs in deionized water (DW). In contrast, the negatively charged SLS did not significantly change the physicochemical properties of the salt-caged NSP. For example, the dissolution rate of the salt-caged NSP containing SLS in DW or pH 1.2 gastric fluid remained over 90% for 2 h. Surfactants for the formulation or dissolution media should be chosen carefully because of their effect on the physicochemical properties and solubilization capacity of salt-caged NSPs containing poorly water-soluble and ionizable drugs via electrostatic molecular interactions.

QbD Consideration for Developing a Double-Layered Tablet into a Single-Layered Tablet with Telmisartan and Amlodipine

The aim of this study was to develop a single-layered version of commercially available Twynstar^® (Telmisartan + Amlodipine) double-layered tablets to improve the dosing convenience. A quality-by-design approach was applied to develop the single-layered version. To evaluate the range and cause of risks for a single-layered tablet in the formulation design research, we used the tools of the risk assessment, initial risk assessment of preliminary hazard analysis and main risk assessment of failure mode and effect analysis to determine the parameters affecting formulation, drug dissolution, and impurities. The critical material attributes were the stabilizer and disintegrant, and the critical process parameters were the wet granulation and tableting process. The optimal range of the design space was determined using the central composite design in the wet granulation and tablet compression processes. The stabilizer, kneading time, and disintegrant of the wet granulation were identified as X values affecting Y values. The compression force and turret speed in the tablet compression were identified as X values affecting Y values. After deciding on the design space with the deduced Y values, the single-layered tablets were formulated, and their dissolution patterns were compared with that of the double-layered tablet. The selected quality-by-design (QbD) approach single-layered tablet formulated using design space were found to be bioequivalent to the Twynstar^® double-layered tablets. Hence, the development of single-layered tablets with two API using the QbD approach could improve the medication compliance of patients and could be used as a platform to overcome time-consuming and excessive costs and the technical and commercial limitations related to various multi-layered tablets.