Deformation behaviors of tolbutamide, hydroxypropyl-beta-cyclodextrin, and their dispersions

Transformation of nanoparticles into compacts: A study on PLGA and celecoxib nanoparticles

Oral delivery of nanoparticles possesses many advantages for delivery of active pharmaceutical ingredients (APIs) to the gastrointestinal tract. However, the poor physical stability of nanoparticles in liquid state is often a challenge. Removing water from the nanosuspensions and transforming the nanoparticles into solid particulate matter in the form of, e.g., tablets could be a potential approach to increase the stability of nanoparticles. The aim of this study was to transform nanoparticles into compacts and to investigate the redispersion of nanoparticles from compacts as well as the dissolution behavior of these compacts. DL-lactide-co-glycolide copolymer (PLGA) nanoparticles and celecoxib (CLX) nanoparticles were used as two model nanoparticle systems and fabricated into nano-embedded microparticles (NEMs) and subsequently compressed into compacts. The compacts were evaluated with respect to the redispersibility of the nanoparticles, as well as the dissolution characteristics of CLX. The results showed that the NEMs could be readily compressed into compacts with sufficient mechanical strength. The size of the redispersed PLGA nanoparticles from the compacts using 2-hydroxypropyl-β-cyclodextrin (HPβCD) as stabilizer was comparable to the original nanoparticles. In contrast, the redispersibility of CLX nanoparticles from the compacts was not as effective as for the PLGA nanoparticles evidenced by a significant increase in the size and polydispersity index (PDI) of the redispersed nanoparticles. Nonetheless, an obvious enhancement in dissolution rate of CLX was observed from the compacts with CLX nanoparticles. It is concluded that transforming polymeric nanoparticles into compacts via NEMs provides stabilization and allows redispersion into original nanoparticles. Despite the reduced redispersibility, compacts loaded with nanoparticles exhibited improved dissolution rate compared with the crystalline drug. Loading of nanoparticles into compacts is a promising approach to overcome the poor stability of nanoparticle within oral drug delivery of nanoparticles.

Capsaicin-Cyclodextrin Complex Enhances Mepivacaine Targeting and Improves Local Anesthesia in Inflamed Tissues

Acidic environments, such as in inflamed tissues, favor the charged form of local anesthetics (LA). Hence, these drugs show less cell permeation and diminished potency. Since the analgesic capsaicin (CAP) triggers opening of the TRPV1 receptor pore, its combination with LAs could result in better uptake and improved anesthesia. We tested the above hypothesis and report here for the first time the analgesia effect of a two-drug combination (LA and CAP) on an inflamed tissue. First, CAP solubility increased up to 20 times with hydroxypropyl-beta-cyclodextrin (HP-β-CD), as shown by the phase solubility study. The resulting complex (HP-β-CD-CAP) showed 1:1 stoichiometry and high association constant, according to phase-solubility diagrams and isothermal titration calorimetry data. The inclusion complex formation was also confirmed and characterized by differential scanning calorimetry (DSC), X-ray diffraction, and ¹H-NMR. The freeze-dried complex showed physicochemical stability for at least 12 months. To test in vivo performance, we used a pain model based on mouse paw edema. Results showed that 2% mepivacaine injection failed to anesthetize mice inflamed paw, but its combination with complexed CAP resulted in pain control up to 45 min. These promising results encourages deeper research of CAP as an adjuvant for anesthesia in inflamed tissues and cyclodextrin as a solubilizing agent for targeting molecules in drug delivery.

Molecular dynamic simulations of ocular tablet dissolution

Small tablets for implantation into the subconjunctival space in the eye are being developed to inhibit scarring after glaucoma filtration surgery (GFS). There is a need to evaluate drug dissolution at the molecular level to determine how the chemical structure of the active may correlate with dissolution in the nonsink conditions of the conjunctival space. We conducted molecular dynamics simulations to study the dissolution process of tablets derived from two drugs that can inhibit fibrosis after GFS, 5-fluorouracil (5-FU) and the matrix metalloprotease inhibitor (MMPi), ilomastat. The dissolution was simulated in the presence of simple point charge (SPC) water molecules, and the liquid turnover of the aqueous humor in the subconjunctival space was simulated by removal of the dissolved drug molecules at regular intervals and replacement by new water molecules. At the end of the simulation, the total molecular solvent accessible surface area of 5-FU tablets increased by 60 times more than that of ilomastat as a result of tablet swelling and release of molecules into solution. The tablet dissolution pattern shown in our molecular dynamic simulations tends to correlate with experimental release profiles. This work indicates that a series of molecular dynamic simulations can be used to predict the influence of the molecular properties of a drug on its dissolution profile and could be useful during preformulation where sufficient amounts of the drug are not always available to perform dissolution studies.

Predictive and correlative techniques for the design, optimisation and manufacture of solid dosage forms

There is much interest in predicting the properties of pharmaceutical dosage forms from the properties of the raw materials they contain. Achieving this with reasonable accuracy would aid the faster development and manufacture of dosage forms. A variety of approaches to prediction or correlation of properties are reviewed. These approaches have variable accuracy, with no single technique yet able to provide an accurate prediction of the overall properties of the dosage form. However, there have been some successes in predicting trends within a formulation series based on the physicochemical and mechanical properties of raw materials, predicting process scale-up through mechanical characterisation of materials and predicting product characteristics by process monitoring. Advances in information technology have increased predictive capability and accuracy by facilitating the analysis of complex multivariate data, mapping formulation characteristics and capturing past knowledge and experience.

Influence of the punch diameter and curvature on the yield pressure of MCC-compacts during Heckel analysis

The volume reduction behaviour of powders has been quantified by means of the 'in-die' yield pressure (YP) using Heckel analysis. However, because different YPs are reported for the same material, the experimental conditions influencing this material-constant were investigated. Silicified microcrystalline cellulose was compressed into flat-faced and convex tablets using a compaction simulator instrumented with load and displacement transducers. During compression, upper and lower punch force and displacement data were recorded and corrected for punch deformation. A symmetrical triangle wave compression profile was used and the instantaneous punch velocity was kept constant (5mm/s). Individual tablet height and weight were used for Heckel analysis. The influence of the 'effective compression pressure' (P(EFF)) (ranging from 10 to 350 MPa), punch diameter (PD) (4, 9.5 and 12 mm) and filling depth (FD) (4.5, 7.5 and 10.5mm) on YP was statistically evaluated using Response Surface Modelling software. A quadratic surface response equation, describing the relationship between P(EFF), PD, FD and YP, was proposed for concave (Adj R(2): 0.8424; S.D.: 14.60 MPa) and flat-faced (Adj R(2): 0.8409; S.D.: 4.49 MPa) punches. YP and tensile strength were mainly determined by P(EFF), irrespective of punch curvature. FD and PD had only a minor influence on the YP, although more pronounced for the concave punches. The method used resulted in reproducible P(EFF) and tensile strength values and the flat-faced tablets showed less weight variation. Flat-faced punches are preferred over punches with a concave surface when investigating the volume reduction behaviour of a powder by means of Heckel analysis and the experimental parameters should be reported.

Complexation with tolbutamide modifies the physicochemical and tableting properties of hydroxypropyl-beta-cyclodextrin

The physicochemical and tableting properties of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and its tolbutamide (TBM) complex were studied. The kinetics of TBM/HP-beta-CD inclusion complex formation in solution were determined by the phase solubility method. Solid complexes were prepared by freeze-drying and spray-drying. Water sorption-desorption behaviour of the materials were studied and compacts were made using a compaction simulator. TBM and HP-beta-CD formed 1:1 inclusion complexes in aqueous solution with an apparent stability constant of 63 M(-1). HP-beta-CDs and TBM/HP-beta-CD complexes were amorphous whereas the freeze-dried and spray-dried TBMs were polymorphic forms II and I, respectively. Sorption-desorption studies showed that HP-beta-CDs were deliquescent at high relative humidities. TBM/HP-beta-CD complexes had slightly lower water contents at low relative humidities than the physical mixtures. However, at high humidities their water sorption and desorption behaviours were similar to those of corresponding physical mixtures, indicating a glass transition of the complexed materials. TBM/HP-beta-CD complexes demonstrated a worse compactability than similarly prepared HP-beta-CDs or physical mixtures. Also particle properties that resulted from these preparation methods affected the compactability of the materials. In conclusion, the physicochemical and tableting properties of HP-beta-CD were modified by complexation it with TBM.