Dissolution and Solubility Enhancement of the Highly Lipophilic Drug Phenytoin via Interaction with Poly(N-isopropylacrylamide-co-vinylpyrrolidone) Excipients

Improvement of solubility, dissolution, and bioavailability of phenytoin intercalated in Mg-Al layered double hydroxide

Layered double hydroxides (LDHs) are highly effective drug delivery systems, owing to their capacity to intercalate or adsorb biomaterials, flexible structure, swelling property, high stability, good biocompatibility, and ease of synthesis. Phenytoin (PHT) is an antiseizure BCS (Biopharmaceutics Classification System) class II drug, presenting low aqueous solubility. Therefore, the current study aimed at increasing its solubility, dissolution, and bioavailability. PHT was intercalated to the MgAl-LDH formed in situ and successful intercalation to form MgAl-PHT-LDH was confirmed by FTIR, PXRD, DSC, and TGA. Examination of particle size and morphology (by photon correlation spectroscopy and electron microscopy, respectively) confirmed the formation and intercalation of nanostructured LDH. Intercalation enhanced the saturation solubility of PHT at 25°C in 0.1N HCl and phosphate buffer (pH 6.8) by 6.57 and 10.5 times respectively. The selected drug excipient powder blend for the formulation of MgAl-PHT-LDH tablets exhibited satisfactory properties in both pre-compression parameters (angle of repose, bulk density, tapped density, Carr's index, and Hausner ratio) and tablet characteristics (weight variation, thickness, hardness, friability, content uniformity, and disintegration time). MgAl-PHT-LDH tablets showed better dissolution of PHT compared to unprocessed PHT tablets at all time points. Oral bioavailability of MgAl-PHT-LDH tablets and unprocessed PHT tablets was tested in two groups of Sprague Dawley rats based on analysis of serum levels of both forms of PHT by UPLC-ESI-MS/MS serum. MgAl-PHT-LDH tablets demonstrated a relative bioavailability of 130.15% compared to unprocessed PHT tablets, confirming a significantly higher oral bioavailability of MgAl-PHT-LDH. In conclusion, MgAl-PHT-LDH could provide a strategy for enhancing solubility, dissolution, and thereby bioavailability of PHT, enabling the evaluation of theclinical efficacy of MgAl-PHT-LDH tablets for the treatment of seizures at lower PHT doses.

Dietary Influence on Drug Efficacy: A Comprehensive Review of Ketogenic Diet-Pharmacotherapy Interactions

It is widely acknowledged that the ketogenic diet (KD) has positive physiological effects as well as therapeutic benefits, particularly in the treatment of chronic diseases. Maintaining nutritional ketosis is of utmost importance in the KD, as it provides numerous health advantages such as an enhanced lipid profile, heightened insulin sensitivity, decreased blood glucose levels, and the modulation of diverse neurotransmitters. Nevertheless, the integration of the KD with pharmacotherapeutic regimens necessitates careful consideration. Due to changes in their absorption, distribution, metabolism, or elimination, the KD can impact the pharmacokinetics of various medications, including anti-diabetic, anti-epileptic, and cardiovascular drugs. Furthermore, the KD, which is characterised by the intake of meals rich in fats, has the potential to impact the pharmacokinetics of specific medications with high lipophilicity, hence enhancing their absorption and bioavailability. However, the pharmacodynamic aspects of the KD, in conjunction with various pharmaceutical interventions, can provide either advantageous or detrimental synergistic outcomes. Therefore, it is important to consider the pharmacokinetic and pharmacodynamic interactions that may arise between the KD and various drugs. This assessment is essential not only for ensuring patients' compliance with treatment but also for optimising the overall therapeutic outcome, particularly by mitigating adverse reactions. This highlights the significance and necessity of tailoring pharmacological and dietetic therapies in order to enhance the effectiveness and safety of this comprehensive approach to managing chronic diseases.

Screening of Organic Small Molecule Excipients on Ternary Solid Dispersions Based on Miscibility and Hydrogen Bonding Analysis: Experiments and Molecular Simulation

The preparation of solid dispersions by mixing insoluble drugs with polymers is the main way to improve the aqueous solubility of drugs. The introduction of organic small molecule excipients into binary solid dispersions is expected to further enhance drug solubility by regulating intermolecular hydrogen bonding within the system at the microscopic level. In this study, we used carbamazepine (CBZ) as the target drug and polyvinylpyrrolidone as the solid dispersion matrix and screened the third component from 13 organic small molecules with good miscibility in the solid dispersion based on the principle of similarity of solubility parameters. The hydrogen bonding parameters and dissociation Gibbs free energy of the 13 organic small molecule-CBZ dimer were calculated by quantum mechanical simulation, and the tryptophan (Try) was identified as the optimal third component of organic small molecule. The migration of CBZ in binary and ternary systems was also analyzed by molecular dynamics simulation. On this theoretical basis, the corresponding solid dispersions were prepared, characterized, and tested for solubility analysis, which verified that the drug solubility was stronger for the system with the addition of polar fractions and the Try was indeed the best third component of organic small molecule compound, which was consistent with the simulation predictions. This screening method may provide theoretical guidance for drug modification design and clinical studies.

Hydrogen Bonding Principle-Based Molecular Design of a Polymer Excipient and Impacts on Hydrophobic Drug Properties: Molecular Simulation and Experiment

Although some commercial excipients for improving the solubility of highly crystalline drugs are widely used, they still cannot cover all types of hydrophobic drugs. In this regard, with phenytoin as the target drug, related molecular structures of polymer excipients were designed. The optimal repeating units of NiPAm and HEAm were screened out through quantum mechanical simulation and Monte Carlo simulation methods, and the copolymerization ratio was also determined. Using molecular dynamics simulation technology, it was confirmed that the dispersibility and intermolecular hydrogen bonds of phenytoin in the designed copolymer were better than those in the commercial PVP materials. At the same time, the designed copolymers and solid dispersions were also prepared during the experiment, and the improvement of their solubility was confirmed, which is in accordance with the simulation predictions. The new ideas and simulation technology may be used for drug modification and development.

No Detectable Phenytoin Plasma Levels After Topical Phenytoin Cream Application in Chronic Pain: Inferences for Mechanisms of Action

Purpose

Topical phenytoin can act as an analgesic in chronic pain, but it is unclear if topical phenytoin gives rise to systemic side effects. Therefore, the aim of this study is: 1) to evaluate safety in chronic pain patients who used topical phenytoin up to 30% applied daily on intact skin and mucous membrane, through determining phenytoin plasma levels; and 2) to elaborate on the analgesic mechanism of action.

Patients and Methods

In this retrospective study, we collected demographic and clinical data from 33 chronic pain patients who used 10% to 30% phenytoin cream, and in whom blood samples were drawn for phenytoin concentration measurement between January 2017 until September 2020. The instruction was to withdraw blood 1 to 4 hours after the last topical phenytoin application. The primary outcome was the detectability of plasma phenytoin after daily use of topical phenytoin.

Results

Blood withdrawal was carried out after on average 14 treatment days with topical phenytoin and on average 2.5 hours after topical phenytoin application. The median daily applied amount of phenytoin cream was 1.2 grams, resulting in a median daily amount of 120 mg phenytoin on the skin. Phenytoin levels were below the limit of detection in all patients and no side effects were reported.

Conclusion

Plasma phenytoin levels were below the limit of detection after topical use of phenytoin cream formulations up to 30% on intact skin and mucous membrane for the treatment of chronic pain, without side effects emerging. This finding suggests that the mechanism of analgesic action resides in the skin.

Phenytoin-loaded bioactive nanoparticles for the treatment of diabetic pressure ulcers: formulation and in vitro/in vivo evaluation

Drug repurposing offers the chance to explore the full potential of existing drugs while reducing drug development time and costs. For instance, the anticonvulsant drug phenytoin (PHT) has been investigated for its wound healing properties. However, its poor solubility and variability of doses used topically limit its use. Hence, the aim of this study was to improve the properties and wound healing efficacy of PHT for the treatment of diabetic bedsores. PHT was encapsulated, using a modified ionic gelation method, in either positively or negatively charged chitosan-alginate nanoparticles (NPs), which possess previously demonstrated wound healing potential. These NPs were characterized by transmission electron microscopy, differential scanning calorimetry, and Fourier-transform infrared spectroscopy. PHT-loaded NPs were evaluated in vivo for their pressure ulcers' healing potential using diabetic rats. The prepared NPs, especially the positively charged particles, exhibited superior wound healing efficacy compared to PHT suspension, with respect to healing rates, granulation tissue formation, tissue maturation, and collagen content. The positively charged NPs resulted in a 56.54% wound closure at day 7, compared to 37% for PHT suspension. Moreover, skin treated with these NPs showed a mature dermis structure with skin appendages, which were absent in all other groups, in addition to the highest collagen content of 63.65%. In conclusion, the use of a bioactive carrier enhanced the healing properties of PHT and allowed the use of relatively low doses of the drug. Our findings suggest that the prepared NPs offer an effective antibiotic-free delivery system for diabetic wound healing applications.

Critical Excipient Properties for the Dissolution Enhancement of Phenytoin

Solubility-enhancing amorphous solid dispersions can aid in the oral delivery of hydrophobic, poorly soluble drugs. Effective solid dispersion excipients enable high supersaturation drug concentrations over biologically relevant time scales. The critical characteristics of an excipient that allow it to work well in a solid dispersion system are not well understood. We prepared poly(N-isopropylacrylamide), poly(N,N-dimethylacrylamide), and poly(N-hydroxyethylacrylamide) excipients of varying molar mass and examined their ability to improve the aqueous solubility of phenytoin, a Biopharmaceutical Class System Class II drug. Binary and ternary solid dispersions of phenytoin and these excipients, along with hydroxypropyl methylcellulose acetate succinate and hydroxypropyl methylcellulose, were prepared at 10 wt % drug loading. Dissolution behavior was studied at early time points (<1 min) and over the course of 6 h. Performance of the ternary solid dispersions was largely a function of the concentration of poly(N-isopropylacrylamide) present in micellar structures and the concentration of PNiPAm micelles in the dissolution media. We present several systems that achieved significant improvement of phenytoin solubility over a wide composition range at enhancement factors among the highest seen to date for phenytoin.

Comparisons of in vitro Fick's first law, lipolysis, and in vivo rat models for oral absorption on BCS II drugs in SNEDDS

Purpose

The objective of this study was to compare the in vitro Fick’s first law, in vitro lipolysis, and in vivo rat assays for oral absorption of Biopharmaceutical Classification Systems Class II (BCS II) drugs in self-nanoemulsifying drug delivery system (SNEDDS), and studied drugs and oils properties effects on the absorption.

Methods

The transport abilities of griseofulvin (GRI), phenytoin (PHE), indomethacin (IND), and ketoprofen (KET) in saturated water solutions and SNEDDS were investigated using the in vitro Madin-Darby canine kidney cell model. GRI and cinnarizine (CIN) in medium-chain triglycerides (MCT)-SNEDDS and long-chain triglycerides (LCT)-SNEDDS were administered in the in vivo SD rat and in vitro lipolysis models to compare the oral absorption and the distribution behaviors in GIT and build an in vitro-in vivo correlation (IVIVC).

Results

In the cell model, the solubility of GRI, PHE, IND, and KET increased 6–8 fold by SNEDDS, but their permeability were only 18%, 4%, 8%, and 33% of those of their saturated water solutions, respectively. However, in vivo absorption of GRI-SNEDDS was twice that of the GRI suspension and those of CIN-SNEDDS were 15–21 fold those of the CIN suspension. In the lipolysis model, the GRI% in aqueous and pellet phases of MCT were similar to that in LCT. In contrast, the CIN% in the aqueous and pellet phases were decreased but that of the lipid phase increased. In addition, an IVIVC was found between the CIN% in the lipid phase and in vivo relative oral bioavailability (F_r).

Conclusion

The in vitro cell model was still a suitable tool to study drug properties effects on biofilm transport and SNEDDS absorption mechanisms. The in vitro lipolysis model provided superior oral absorption simulation of SNEDDS and helped to build correlation with in vivo rats. The oral drug absorption was affected by drug and oil properties in SNEDDS.

Lamotrigine ethanol monosolvate

Lamotrigine is an active pharmaceutical ingredient used as a treatment for epilepsy and psychiatric disorders. Single crystals of an ethano-late solvate, C9H7Cl2N5·C2H5OH, were produced by slow evaporation of a saturated solution from anhydrous ethanol. Within the crystal structure, the lamotrigine mol-ecules form dimers through N-H⋯N hydrogen bonds involving the amine N atoms in the ortho position of the triazine group. These dimers are linked into a tape motif through hydrogen bonds involving the amine N atoms in the para position. The ethanol and lamotrigine are present in a 1:1 ratio in the lattice with the ethyl group of the ethanol mol-ecule exhibiting disorder with an occupancy ratio of 0.516 (14):0.484 (14).

Advances in Polymer Design for Enhancing Oral Drug Solubility and Delivery

Synthetic polymers have enabled amorphous solid dispersions (ASDs) to emerge as an oral delivery strategy for overcoming poor drug solubility in aqueous environments. Modern ASD products noninvasively treat a range of chronic diseases (for example, hepatitis C, cystic fibrosis, and HIV). In such formulations, polymeric carriers generate and maintain drug supersaturation upon dissolution, increasing the apparent drug solubility to enhance gastrointestinal barrier absorption and oral bioavailability. In this Review, we outline several approaches in designing polymeric excipients to drive interactions with active pharmaceutical ingredients (APIs) in spray-dried ASDs, highlighting polymer-drug formulation guidelines from industrial and academic perspectives. Special attention is given to new commercial and specialized polymer design strategies that can solubilize highly hydrophobic APIs and suppress the propensity for rapid drug recrystallization. These molecularly customized excipients and hierarchical excipient assemblies are promising toward informing early-stage drug-discovery development and reformulating existing API candidates into potentially lifesaving oral medicines for our growing global population.

Quantification of six potential unspecific human biomarkers of 1-vinyl-2-pyrrolidone exposure in Sprague-Dawley rat urine using gas chromatography coupled with triple mass spectrometry

RATIONALE

The monomer 1-vinyl-2-pyrrolidone (VP) is a substance with excellent solvent features. It is used in a wide variety of pharmaceutical, cosmetic, food industrial or technical applications and produced on an industrial scale. Since VP has caused adenocarcinoma of the nasal cavity and liver cell carcinoma in long-term experiments with rats, a human biomarker would be appreciated for risk assessment.

METHODS

A sensitive analytical electron ionization gas chromatography/tandem mass spectrometry (GC/MS/MS) method for the determination of six possible biomarkers for VP in urine was established and validated. Two isotope-labeled internal standards (ISTD) were used for quantification. A simple and easy to use freeze-drying step was performed prior to derivatization with N-tert-butyldimethylsilyl-N-methyltrifluoracetamide (MTBSTFA) and following sample extraction for cleanup purposes.

RESULTS

A calibration curve with six calibration standards ranging from 50 μg/L to 2000 μg/L (10-fold higher for H-OPAA) in urine was prepared. Validation results were satisfactory with recoveries ranging from 88.2 to 110.2 % with two exceptions for the lowest quality control for two substances without ISTD (126.4 % and 139.3 %). Three of the substances could be identified as VP metabolites in an exposure study with Sprague-Dawley (SD) rats.

CONCLUSIONS

A quick and easy to use method has been established for six target molecules investigated for a better understanding of the metabolism of VP. Two of three substances identified as metabolites of VP could serve as a nonspecific human biomarker for VP exposure as shown with an excerpt of an exposure study performed in SD rats.

Mesoporous silica materials: From physico-chemical properties to enhanced dissolution of poorly water-soluble drugs

New approaches in pharmaceutical chemistry have resulted in more complex drug molecules in the quest to achieve higher affinity to their targets. However, these 'highly active' drugs can also suffer from poor water solubility. Hence, poorly water soluble drugs became a major challenge in drug formulation, and this problem is increasing, as currently about 40 of the marketed drugs and 90% of drug candidates are classified as poorly water soluble. Various approaches exist to circumvent poor water solubility and poor dissolution rate in aqueous environment, however, each having disadvantages and certain limitations. Recently, mesoporous silica materials (MSMs) have been proposed to be used as matrices for enhancing the apparent solubility and dissolution rate of different drug molecules. MSMs are ideal candidates for this purpose, as silica is a "generally regarded as safe" (GRAS) material, is biodegradable, and can be readily surface-modified in order to optimize drug loading and subsequent release in the human body. The major advantage of mesoporous silica as drug delivery systems (DDSs) for poorly water soluble drugs lies in their pore size, pore morphology, and versatility in alteration of the surface groups, which can result in optimized interactions between a drug candidate and MSM carrier by modifying the pore surfaces. Furthermore, the drug of interest can be loaded into these pores in a preferably amorphous state, which can increase the drug dissolution properties dramatically. The highlights of this review include a critical discussion about the modification of the physico-chemical properties of MSMs and how these physico-chemical modifications influence the drug loading and the subsequent dissolution of poorly water soluble drugs. It aims to further promote the use of MSMs as alternative strategy to common methods like solubility enhancement by cyclodextrins, micronization, or microemulsion techniques. This review can provide guidance on how to tailor MSMs to achieve optimized drug loading and drug dissolution.

The Need for Restructuring the Disordered Science of Amorphous Drug Formulations

The alarming numbers of poorly soluble discovery compounds have centered the efforts towards finding strategies to improve the solubility. One of the attractive approaches to enhance solubility is via amorphization despite the stability issue associated with it. Although the number of amorphous-based research reports has increased tremendously after year 2000, little is known on the current research practice in designing amorphous formulation and how it has changed after the concept of solid dispersion was first introduced decades ago. In this review we try to answer the following questions: What model compounds and excipients have been used in amorphous-based research? How were these two components selected and prepared? What methods have been used to assess the performance of amorphous formulation? What methodology have evolved and/or been standardized since amorphous-based formulation was first introduced and to what extent have we embraced on new methods? Is the extent of research mirrored in the number of marketed amorphous drug products? We have summarized the history and evolution of amorphous formulation and discuss the current status of amorphous formulation-related research practice. We also explore the potential uses of old experimental methods and how they can be used in tandem with computational tools in designing amorphous formulation more efficiently than the traditional trial-and-error approach.

Enhanced Performance of Blended Polymer Excipients in Delivering a Hydrophobic Drug through the Synergistic Action of Micelles and HPMCAS

Blends of hydroxypropyl methylcellulose acetate succinate (HPMCAS) and dodecyl (C₁₂)-tailed poly(N-isopropylacrylamide) (PNIPAm) were systematically explored as a model system to dispense the active ingredient phenytoin by rapid dissolution, followed by the suppression of drug crystallization for an extended period. Dynamic and static light scattering revealed that C₁₂-PNIPAm polymers, synthesized by reversible addition-fragmentation chain-transfer polymerization, self-assembled into micelles with dodecyl cores in phosphate-buffered saline (PBS, pH 6.5). A synergistic effect on drug supersaturation was documented during in vitro dissolution tests by varying the blending ratio, with HPMACS primarily aiding in rapid dissolution and PNIPAm maintaining supersaturation. Polarized light and cryogenic transmission electron microscopy experiments revealed that C₁₂-PNIPAm micelles maintain drug supersaturation by inhibiting both crystal nucleation and growth. Cross-peaks between the phenyl group of phenytoin and the isopropyl group of C₁₂-PNIPAm in 2D ¹H nuclear Overhauser effect (NOESY) spectra confirmed the existence of drug-polymer intermolecular interactions in solution. Phenytoin and polymer diffusion coefficients, measured by diffusion-ordered NMR spectroscopy (DOSY), demonstrated that the drug-polymer association constant increased with increasing local density of the corona chains, coincident with a reduction in C₁₂-PNIPAm molecular weight. These findings demonstrate a new strategy for exploiting the versatility of polymer blends through the use of self-assembled micelles in the design of advanced excipients.

High-Throughput Excipient Discovery Enables Oral Delivery of Poorly Soluble Pharmaceuticals

Polymeric excipients are crucial ingredients in modern pills, increasing the therapeutic bioavailability, safety, stability, and accessibility of lifesaving products to combat diseases in developed and developing countries worldwide. Because many early-pipeline drugs are clinically intractable due to hydrophobicity and crystallinity, new solubilizing excipients can reposition successful and even failed compounds to more effective and inexpensive oral formulations. With assistance from high-throughput controlled polymerization and screening tools, we employed a strategic, molecular evolution approach to systematically modulate designer excipients based on the cyclic imide chemical groups of an important (yet relatively insoluble) drug phenytoin. In these acrylamide- and methacrylate-containing polymers, a synthon approach was employed: one monomer served as a precipitation inhibitor for phenytoin recrystallization, while the comonomer provided hydrophilicity. Systems that maintained drug supersaturation in amorphous solid dispersions were identified with molecular-level understanding of noncovalent interactions using NOESY and DOSY NMR spectroscopy. Poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (poly(NIPAm-co-DMA)) at 70 mol % NIPAm exhibited the highest drug solubilization, in which phenytoin associated with inhibiting NIPAm units only with lowered diffusivity in solution. In vitro dissolution tests of select spray-dried dispersions corroborated the screening trends between polymer chemical composition and solubilization performance, where the best NIPAm/DMA polymer elevated the mean area-under-the-dissolution-curve by 21 times its crystalline state at 10 wt % drug loading. When administered to rats for pharmacokinetic evaluation, the same leading poly(NIPAm-co-DMA) formulation tripled the oral bioavailability compared to a leading commercial excipient, HPMCAS, and translated to a remarkable 23-fold improvement over crystalline phenytoin.

From N-vinylpyrrolidone anions to modified paraffin-like oligomers via double alkylation with 1,8-dibromooctane: access to covalent networks and oligomeric amines for dye attachment

The double alkylation of N-vinylpyrrolidone (N-VP) with 1,8-dibromooctane yields paraffin-like oligomeric chains bearing polymerizable vinyl moieties. These oligomers were radically crosslinked in bulk with N-VP as co-monomer yielding swellable polymer disks. The vinylic side groups of the N-VP oligomers allow thiol–ene click reactions with 2-aminoethanethiol hydrochloride to obtain reactive amino-functionalized oligomers. Further modification of the free amino groups with 1,4-difluoro-9,10-anthraquinone (DFA) yields red-colored oligomeric anthraquinone dyes. The final reaction of DFA-substituted N-VP oligomers with Jeffamine^® M 600 leads to blue-colored and branched oligomers with poly(ethylene glycol) side chains.

Deconstructing HPMCAS: Excipient Design to Tailor Polymer-Drug Interactions for Oral Drug Delivery

Spray-dried dispersions (SDDs) are fascinating polymer-drug mixtures that exploit the amorphous state of a drug to dramatically elevate its apparent aqueous solubility above equilibrium. For practical usage in oral delivery, understanding how polymers mechanistically provide physical stability during storage and prevent supersaturated drugs from succumbing to precipitation during dissolution remains a formidable challenge. To this end, we developed a versatile polymeric platform with functional groups analogous to hydroxypropyl methyl cellulose acetate succinate (HPMCAS, a heterogeneous leading excipient candidate for SDDs) and studied its interactions with Biopharmaceutical Classification System Class II drug models probucol, danazol, and phenytoin at various dosages. By conducting reversible addition-fragmentation chain transfer polymerizations with monomeric components chemically analogous to HPMCAS, we synthetically dismantled the highly polydisperse architecture of HPMCAS into well-defined polymer systems (i.e., targetable M_n, Đ < 1.3, tunable T_g). In the powdered SDD form, by wide-angle X-ray diffraction all HPMCAS analogs yielded amorphous danazol and phenytoin up to 50 wt % loading, whereas for probucol, hydrophobic methoxy functionality and high polymeric T_g were key to inhibit immediate partitioning into crystalline domains. Nonsink in vitro dissolution tests revealed distinct release profiles. The polymer containing only acetyl and succinoyl substituents spray-dried with probucol increased the area under the dissolution curve by a factor of 180, 112, and 26 over pure drug at 10, 25, and 50 wt % loading, respectively. For crystallization-prone danazol and phenytoin, we observed that the water-soluble polymer with hydroxyl groups inhibited crystal growth and enabled high burst release and supersaturation maintenance. Our findings provide fundamental insight into how excipient microstructures can complex with drugs for excipient formulation applications.