Insight into the solubility and dissolution behavior of piroxicam anhydrate and monohydrate forms

Solubility-permeability interplay of hydrotropic solubilization of piroxicam

OBJECTIVES

In this research paper, an investigation has been made to assess the simultaneous effect of a solubility enhancement approach, i.e., hydrotropy on the solubility and apparent permeability of piroxicam. The solubility of piroxicam (PRX) a BCS (biopharmaceutics classification system) class II drug has been increased using a mixed hydrotropy approach. This study is based on identifying the pattern of solubility-permeability interplay and confirming whether every solubility gain results in a concomitant decrease in permeability or permeability remains unaffected.

METHOD

Solid dispersions of PRX were formulated using two hydrotropes, viz., sodium benzoate (SB) and piperazine (PP) by solvent evaporation method. A comprehensive 32factorial design was employed to study the effect of hydrotropes on the solubility and permeability of PRX. Subsequently, PRX tablets containing these solid dispersions were formulated and evaluated.

KEY FINDINGS

SB and PP displayed a significant increase in the solubility of PRX ranging from 0.99 to 2.21 mg/mL for F1-F9 batches attributed to the synergistic effect of hydrotropes. However, there is a reduction in PRX permeability with increasing hydrotrope levels. The decline in permeability was notably less pronounced compared to the simultaneous rise in aqueous solubility of PRX.

CONCLUSION

An evident tradeoff between permeability and solubility emerged through the mixed hydrotropic solubilization for PRX. As PRX has generally higher intrinsic permeability, it has been assumed that this permeability loss will not affect the overall absorption of PRX. However, it may affect the absorption of drugs with limited permeability. Therefore, solubility permeability interplay should be investigated during solubility enhancement.

Preparation and Investigation of a Nanosized Piroxicam Containing Orodispersible Lyophilizate

Non-steroidal anti-inflammatory piroxicam (PRX) is a poorly water-soluble drug that provides relief in different arthritides. Reducing the particle size of PRX increases its bioavailability. For pediatric, geriatric, and dysphagic patients, oral dispersible systems ease administration. Moreover, fast disintegration followed by drug release and absorption through the oral mucosa can induce rapid systemic effects. We aimed to produce an orodispersible lyophilizate (OL) consisting of nanosized PRX. PRX was solved in ethyl acetate and then sonicated into a poloxamer-188 solution to perform spray-ultrasound-assisted solvent diffusion-based nanoprecipitation. The solid form was formulated via freeze drying in blister sockets. Mannitol and sodium alginate were applied as excipients. Dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) were used to determine the particle size. The morphology was characterized by scanning electron microscopy (SEM). To establish the crystallinity, X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) were used. A disintegration and in vitro dissolution test were performed. DLS and NTA presented a nanosized PRX diameter. The SEM pictures showed a porous structure. PRX became amorphous according to the XRPD and DSC curves. The disintegration time was less than 1 min and the dissolution profile improved. The final product was an innovative anti-inflammatory drug delivery system.

Development of piroxicam mini-tablets enabled by spherical cocrystallization

We examined the potential of the spherical cocrystallization (SCC) technology in simultaneously enhancing tablet manufacturability and dissolution of poorly soluble drugs by developing a mini-tablet formulation of piroxicam. The manufacturing of mini-tablets using a direct compression (DC) process is more challenging than conventional tablets because of the much stricter requirement on the micromeritic properties of formulated powders. The SCC process in this work involved two steps: 1) preparing a new piroxicam-ferulic acid (PRX-FA) cocrystal, and 2) forming spherical agglomerates with the aid of a suitable bridging liquid. The PRX-FA cocrystal exhibited enhanced solubility as well as improved plasticity. The bridging liquid, a mixture of chloroform and ethyl acetate (EA) (1: 2, v/v), was chosen based on the high computed adsorption energy of chloroform and EA on morphologically dominating crystal faces of PRX-FA. The improved flowability, tabletability, and dissolution rate of spherical PRX-FA enabled the successful development of a DC mini-tablet formulation with a high PRX loading (41 wt%). This example shows that SCC is a powerful enabling technology for DC tablet formulation development of challenging drugs.

Solution-Mediated Phase Transformation of Aripiprazole: Negating the Effect of Crystalline Forms on Dissolution and Oral Pharmacokinetics

We aimed to evaluate the effect of crystalline forms of aripiprazole, an antipsychotic drug for schizophrenia, on the dissolution rates and oral pharmacokinetics. Solubility, intrinsic dissolution rates, and tablet dissolution rates of the monohydrate (MA) and the anhydrous form (AA) were measured in various aqueous media while monitoring the phase transformation by ATR-FTIR. And their oral pharmacokinetics in dogs were compared. The intrinsic dissolution rate of MA was lower compared to AA, confirming its thermodynamic stability relative to AA in water. Phase transformations during the solubility measurement were media-dependent: In simulated gastric fluid, both AA and MA changed to HCl salt form, whereas AA and HCl salt form transformed to MA in simulated intestinal fluid. In vitro dissolution rates and dog oral pharmacokinetics of AA and MA tablets were similar. The results suggest that the solution-mediated transformation to HCl salt or MA negates the effect of different crystalline forms on dissolution rates in vivo and, consequently, on oral pharmacokinetics. We emphasize the importance of the dissolution tests employing various bio-relevant media for better prediction of in vivo performance and the selection of a solid form for development.

Solubility Enhancement of Betamethasone, Meloxicam and Piroxicam by Use of Choline-Based Deep Eutectic Solvents

Background: The low aqueous solubility of three important drugs (betamethasone (BETA), meloxicam (MEL) and piroxicam (PIR)) have been increased by use of deep eutectic solvents (DESs) based choline chloride/urea (ChCl/U), choline chloride/ethylene glycol (ChCl/EG) and choline chloride/glycerol (ChCl/G) as new class of solvents at T = (298.15 to 313.15) K. Methods: DESs were prepared by combination of the ChCl/EG, U and G with the molar ratios: 1:2. The solubility of drugs in the aqueous DESs solutions was measured at different temperatures with shake flask method. Results: The solubility of the investigated drugs increased with increasing the weight fraction of DESs. The solubility data were correlated by e-NRTL and Wilson models. Also, the thermodynamic functions, Gibbs energy, enthalpy, and entropy of dissolution were calculated. Conclusion: At the same composition of co-solvents and temperature, the BETA, PIR and MEL solubility was highest in (ChCl/U + water), (ChCl/U + water) and (ChCl/EG + water) respectively. The calculated solubility based on these models was in good agreement with the experimental values. In addition, the results show that, the main contribution for drugs solubility in the aqueous DES solutions is the enthalpy.

Manipulation of Pharmaceutical Polymorphic Transformation Process Using Excipients

BACKGROUND

In the pharmaceutical field, it is vital to ensure a consistent product containing a single solid-state form of the active pharmaceutical ingredient (API) in the drug product. However, some APIs are suffering from the risk of transformation of their target forms during processing, formulation and storage.

METHODS

The purpose of this review is to summarize the relevant category of excipients and demonstrate the availability and importance of using excipients as a key strategy to manipulate pharmaceutical polymorphic transformation.

RESULTS

The excipient effects on solvent-mediated phase transformations, solid-state transitions and amorphous crystallization are significant. Common pharmaceutical excipients including amino acids and derivatives, surfactants, and various polymers and their different manipulation effects were summarized and discussed.

CONCLUSION

Appropriate use of excipients plays a role in manipulating polymorphic transformation process of corresponding APIs, with a promising application of guaranteeing the stability and effectiveness of drug dosage forms.

Quasi-Dynamic Dissolution of Electrospun Polymeric Nanofibers Loaded with Piroxicam

We investigated and monitored in situ the wetting and dissolution properties of polymeric nanofibers and determined the solid-state of a drug during dissolution. Piroxicam (PRX) was used as a low-dose and poorly-soluble model drug, and hydroxypropyl methylcellulose (HPMC) and polydextrose (PD) were used as carrier polymers for electrospinning (ES). The initial-stage dissolution of the nanofibers was monitored in situ with three-dimensional white light microscopic interferometry (SWLI) and high-resolution optical microscopy. The physical solid-state characterization of nanofibers was performed with Raman spectroscopy, X-ray powder diffraction (XRPD), and scanning electron microscopy (SEM). We showed that PRX recrystallizes in a microcrystalline form immediately after wetting of nanofibers, which could lead to enhanced dissolution of drug. Initiation of crystal formation was detected by SWLI, indicating: (1) that PRX was partially released from the nanofibers, and (2) that the solid-state form of PRX changed from amorphous to crystalline. The amount, shape, and size of the PRX crystals depended on the carrier polymer used in the nanofibers and dissolution media (pH). In conclusion, the present nanofibers loaded with PRX exhibit a quasi-dynamic dissolution via recrystallization. SWLI enables a rapid, non-contacting, and non-destructive method for in situ monitoring the early-stage dissolution of nanofibers and regional mapping of crystalline changes (re-crystallization) during wetting. Such analysis is crucial because the wetting and dissolution of nanofibers can greatly influence the performance of nanofibrous drug delivery systems in pharmaceutical and biomedical applications.

Modulation of the Release of a Non-Interacting Low Solubility Drug from Chitosan Pellets Using Different Pellet Size, Composition and Numerical Optimization

Two size classes of piroxicam (PXC) pellets (mini (380–550 μm) and conventional (700–1200 μm)) were prepared using extrusion/spheronization and medium viscosity chitosan (CHS). Mixture experimental design and numerical optimization were applied to distinguish formulations producing high sphericity pellets with fast or extended release. High CHS content required greater wetting liquid volume for pellet formation and the diameter decreased linearly with volume. Sphericity increased with CHS for low-to-medium drug content. Application of PXRD showed that the drug was a mixture of form II and I. Crystallinity decreased due to processing and was significant at 5% drug content. Raman spectroscopy showed no interactions. At pH 1.2, the dissolved CHS increased ‘apparent’ drug solubility up to 0.24 mg/mL while, at pH 5.6, the suspended CHS increased ‘apparent’ solubility to 0.16 mg/mL. Release at pH 1.2 was fast for formulations with intermediate CHS and drug levels. At pH 5.6, conventional pellets showed incomplete release while mini pellets with a CHS/drug ratio ≥2 and up to 21.25% drug, showed an extended release that was completed within 8 h. Numerical optimization provided optimal formulations for fast release at pH 1.2 with drug levels up to 40% as well as for extended release formulations with drug levels of 5% and 10%. The Weibull model described the release kinetics indicating complex or combined release (parameter ‘b’ > 0.75) for release at pH 1.2, and normal diffusion for the mini pellets at pH 5.6 (‘b’ from 0.63 to 0.73). The above results were attributed mainly to the different pellet sizes and the extensive dissolution/erosion of the gel matrix was observed at pH 1.2 but not at pH 5.6.

Aspartame as a co-former in co-amorphous systems

Co-amorphous drug delivery systems are a promising approach to improve the dissolution rate and therefore potentially the oral bioavailability of poorly-water soluble drugs. Several low molecular weight excipients, for instance amino acids, have previously been shown to stabilize the amorphous form and increase the dissolution rate of drugs. In this study, the feasibility of aspartame, a methyl ester of the aspartic acid-phenylalanine dipeptide, as a co-former was investigated and compared with the respective single amino acids, both alone and in combination. The poorly water-soluble compounds mebendazole, tadalafil and piroxicam were chosen as model drugs. In contrast to the single amino acids or the physical mixture of both, all drug-aspartame mixtures became amorphous upon 90 min of ball milling. Only a single glass transition temperature (T_g) was detected by modulated differential scanning calorimetry, which indicates that a homogeneous single-phase co-amorphous system was obtained. Powder dissolution tests showed that the dissolution rates of the drugs from drug-aspartame co-amorphous samples were increased compared to crystalline drugs. Furthermore, supersaturation was observed for the mebendazole-aspartame and tadalafil-aspartame co-amorphous systems. In conclusion, aspartame has been shown to be a promising co-former in co-amorphous systems, superior to the single amino acids or their mixtures.

Piroxicam cocrystals with phenolic coformers: preparation, characterization, and dissolution properties

This study explores the preparation and investigation of dissolution properties of piroxicam cocrystals. Differential scanning calorimetry (DSC) was used to determine the capability of resorcinol (RES), methylparaben (MPB), and vanillin (VAN) to form cocrystals with piroxicam (PRX). Generation of cocrystals was attempted by liquid assisted grinding and slurry methods. Cocrystals were characterized by thermal methods, powder X-ray diffraction, and Fourier-transform infrared spectroscopy. Apparent solubility, intrinsic dissolution rate (IDR), and powder dissolution profile of cocrystals were compared with anhydrous piroxicam, piroxicam monohydrate (PRXMH), and previously reported piroxicam-succinic acid cocrystal. Contact angles and particle sizes of the studied solids were also measured. Based on the DSC screening results, we prepared and characterized PRX-RES and PRX-MPB cocrystals. Interestingly, the cocrystals not only failed to improve apparent solubility and IDR of PRX but also showed lower values than PRX that were attributed to induction of phase transformation of PRX to PRXMH. In contrary, cocrystals performed better than PRX in powder dissolution studies. The higher dissolution rates of cocrystals were explained by improved wettability and reduced sizes. This study has highlighted the complexity of solid state properties of cocrystals and has provided new evidence for the in-solution stability issues of cocrystals.

A comparison of the experimental and theoretical charge density distributions in two polymorphic modifications of piroxicam

Experimental charge density distribution studies of two polymorphic forms of piroxicam, β-piroxicam (1) and piroxicam monohydrate (2), were carried out via high-resolution single crystal X-ray diffraction experiments and multipole refinement. The asymmetric unit of (2) consists of two discrete piroxicam molecules, (2a) and (2b), and two water molecules. Geometry differs between (1) and (2) due to the zwitterionic nature of (2) which results in the rotation of the pyridine ring around the C(10)-N(2) bond by approximately 180°. Consequently, the pyridine and amide are no longer co-planar and (2) forms two exclusive, strong hydrogen bonds, H(3)O(4) and H(2)O(3), with bond energies of 66.14 kJ mol^-1 and 112.82 kJ mol^-1 for (2a), and 58.35 kJ mol^-1 and 159.51 kJ mol^-1 for (2b), respectively. Proton transfer between O(3) and N(3) in (2) results in significant differences in surface electrostatic potentials. This is clarified by the calculation of atomic charges in the zwitterion that shows the formally positive charge of the pyridyl nitrogen which is redistributed over the whole of the pyridine ring instead of concentrating at N-H. Similarly, the negative charge of the oxygen is distributed across the benzothiazine carboxamide moiety. The multipole derived lattice energy for (1) is -304 kJ mol^-1 and that for (2) is -571 kJ mol^-1, which is in agreement with the experimentally determined observations of higher solubility and dissolution rates of (1) compared to (2).

Development of Oromucosal Dosage Forms by Combining Electrospinning and Inkjet Printing

Printing technology has been shown to enable flexible fabrication of solid dosage forms for personalized drug therapy. Several methods can be applied for tailoring the properties of the printed pharmaceuticals. In this study, the use of electrospun fibrous substrates in the fabrication of inkjet-printed dosage forms was investigated. A single-drug formulation with lidocaine hydrochloride (LH) and a combination drug system containing LH and piroxicam (PRX) for oromucosal administration were prepared. The LH was deposited on the electrospun and cross-linked gelatin substrates by inkjet printing, whereas PRX was incorporated within the substrate fibers during electrospinning. The solid state analysis of the electrospun substrates showed that PRX was in an amorphous state within the fibers. Furthermore, the results indicated the entrapment and solidification of the dissolved LH within the fibrous gelatin matrix. The printed drug amount (2-3 mg) was in good correlation with the theoretical dose calculated based on the printing parameters. However, a noticeable degradation of the printed LH was detected after a few months. An immediate release (over 85% drug release after 8 min) of both drugs from the printed dosage forms was observed. In conclusion, the prepared electrospun gelatin scaffolds were shown to be suitable substrates for inkjet printing of oromucosal formulations. The combination of electrospinning and inkjet printing allowed the preparation of a dual drug system.

Enzymatic activity in the presence of surfactants commonly used in dissolution media, Part 1: Pepsin

The United States Pharmacopeia (USP) General Chapters Dissolution 〈711〉 and Disintegration and Dissolution of Dietary Supplements 〈2040〉 allows the use of enzymes in dissolution media when gelatin capsules do not conform to dissolution specifications due to cross linking. Possible interactions between enzymes and surfactants when used together in dissolution media could result in loss of the enzymatic activity. Pepsin is an enzyme commonly used in dissolution media, and in this work, the activity of pepsin was determined in the presence of different surfactants as usually found in case of dissolution tests of certain gelatin capsule formulations. Pepsin enzymatic activity was determined according to the Ninth Edition of the Food Chemicals Codex (FCC) 9 method, in dissolution conditions: simulated gastric fluid, 37 °C and 50 rpm. Sodium dodecyl sulfate (SDS), cetyltrimethyl ammonium bromide (CTAB), polysorbate 80 (Tween 80) and octoxynol 9 (Triton X100) in concentrations above and below their critical micellar concentrations were selected. Results showed a significant reduction in the activity of pepsin at all the concentrations of SDS assayed. On the contrary, CTAB, Tween 80, and Triton X100 did not alter the enzymatic activity at of pepsin any of the concentration assayed. This data demonstrates a rational selection of the surfactant to be used when pepsin is required in dissolution test.

Towards improved solubility of poorly water-soluble drugs: cryogenic co-grinding of piroxicam with carrier polymers

Amorphous solid dispersions (SDs) open up exciting opportunities in formulating poorly water-soluble active pharmaceutical ingredients (APIs). In the present study, novel catalytic pretreated softwood cellulose (CPSC) and polyvinylpyrrolidone (PVP) were investigated as carrier polymers for preparing and stabilizing cryogenic co-ground SDs of poorly water-soluble piroxicam (PRX). CPSC was isolated from pine wood (Pinus sylvestris). Raman and Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) were used for characterizing the solid-state changes and drug-polymer interactions. High-resolution scanning electron microscope (SEM) was used to analyze the particle size and surface morphology of starting materials and final cryogenic co-ground SDs. In addition, the molecular aspects of drug-polymer interactions and stabilization mechanisms are presented. The results showed that the carrier polymer influenced both the degree of amorphization of PRX and stabilization against crystallization. The cryogenic co-ground SDs prepared from PVP showed an enhanced dissolution rate of PRX, while the corresponding SDs prepared from CPSC exhibited a clear sustained release behavior. In conclusion, cryogenic co-grinding provides a versatile method for preparing amorphous SDs of poorly water-soluble APIs. The solid-state stability and dissolution behavior of such co-ground SDs are to a great extent dependent on the carrier polymer used.

Amorphous solid dispersions of piroxicam and Soluplus(®): Qualitative and quantitative analysis of piroxicam recrystallization during storage

The conversion of active pharmaceutical ingredient (API) from amorphous to crystalline form is the primary stability issue in formulating amorphous solid dispersions (SDs). The aim of the present study was to carry out qualitative and quantitative analysis of the physical solid-state stability of the SDs of poorly water-soluble piroxicam (PRX) and polyvinyl caprolactam-polyvinyl acetate-polyethylene-glycol graft copolymer (Soluplus(®)). The SDs were prepared by a solvent evaporation method and stored for six months at 0% RH/6 °C, 0% RH/25 °C, 40% RH/25 °C and 75% RH/25 °C. Fourier transform infrared spectroscopy equipped with attenuated total reflection accessory (ATR-FTIR) and Raman spectroscopy were used for characterizing the physical solid-state changes and drug-polymer interactions. The principal component analysis (PCA) and multivariate curve resolution alternating least squares (MCR-ALS) were used for the qualitative and quantitative analysis of Raman spectra collected during storage. When stored at 0% RH/6 °C and at 0% RH/25 °C, PRX in SDs remained in an amorphous form since no recrystallization was observed by ATR-FTIR and Raman spectroscopy. Raman spectroscopy coupled with PCA and MCR-ALS and ATR-FTIR spectroscopy enabled to detect the recrystallization of amorphous PRX in the samples stored at higher humidity.

Soluplus graft copolymer: potential novel carrier polymer in electrospinning of nanofibrous drug delivery systems for wound therapy

Electrospinning is an effective method in preparing polymeric nanofibrous drug delivery systems (DDSs) for topical wound healing and skin burn therapy applications. The aim of the present study was to investigate a new synthetic graft copolymer (Soluplus) as a hydrophilic carrier polymer in electrospinning of nanofibrous DDSs. Soluplus (polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft copolymer (PCL-PVAc-PEG)) was applied in the nonwoven nanomats loaded with piroxicam (PRX) as a poorly water-soluble drug. Raman spectroscopy, X-ray powder diffraction, differential scanning calorimetry, and scanning electron microscopy (SEM) were used in the physical characterization of nanofibrous DDSs. According to the SEM results, the drug-loaded PCL-PVAc-PEG nanofibers were circular in cross-section with an average diameter ranging from 500 nm up to 2 µm. Electrospinning stabilized the amorphous state of PRX. In addition, consistent and sustained-release profile was achieved with the present nanofibrous DDSs at the physiologically relevant temperature and pH applicable in wound healing therapy. In conclusion, electrospinning can be used to prepare nanofibrous DDSs of PCL-PVAc-PEG graft copolymer (Soluplus) and to stabilize the amorphous state of a poorly water-soluble PRX. The use of this synthetic graft copolymer can open new options to formulate nanofibrous DDSs for wound healing.