The effect of a semi-permeable, strengthening fiber coating on the expansion, mechanical properties, and residence time of gastroretentive fibrous dosage forms

Recently, we have shown in dogs that the gastric residence time of expandable fibrous dosage forms can be prolonged by coating the fibers with a semi-permeable, strengthening coating. In this work on pigs, the effect of the volume fraction of the coating, φc, on the expansion, mechanical strength, and gastric residence time is investigated. Three methacrylic acid-ethyl acrylate-coated fibrous dosage forms with φc = 0.025, 0.041, and 0.068 were prepared and tested. Upon administering to a pig, the dosage forms expanded to a normalized radial expansion of 0.5-0.6 in 5, 8, and 10 h, respectively. The expanded dosage forms resided in the stomach and fragmented after 11, 25, and 31 h. The fragments then passed into the intestines and dissolved in 2-3 h. Models suggest that upon contact with gastric fluid, a hydrostatic pressure develops in the fibers due to the inward diffusion of water. The hydrostatic pressure in turn induces a tensile stress in the coating and the dosage form expands. The tensile stress and the expansion rate are inversely proportional to φc. The expanded dosage form eventually fractures due to the loads applied by the contracting stomach walls. The post-expansion mechanical strength and the time to fracture increase steeply with φc. The models predict the experimental results reasonably well. Thus, by increasing φc, dosage form fracture is delayed and the gastric residence time prolonged.

Solid-solution fibrous dosage forms for immediate delivery of sparingly-soluble drugs: Part 2. 3D-micro-patterned dosage forms

In part 1, we have investigated drug release by solid-solution single fibers comprising a sparingly water-soluble drug (ibuprofen) and a highly water-soluble dual excipient (low-molecular-weight hydroxypropyl methyl cellulose (HPMC) and polyoxyl stearate (POS)). In this part, fibrous dosage forms of the same formulation are prepared by 3D-micro-patterning, tested, and modeled. Upon immersion in a small volume of dissolution fluid, the dosage forms rapidly swelled and formed a low-viscosity medium, which subsequently dissolved. The dissolution time increased slightly with volume fraction of the fibers, φ_s, in the solid dosage form, but was less than 25 minutes even up to φ_s = 0.65. After dosage form dissolution, the fluid was supersaturated by a factor of two; the drug concentration then gradually decreased to solubility. The solubility was proportional to the concentration of POS, and was enhanced by a factor of six at φ_s = 0.65 (the most densely-packed dosage form). Theoretical models suggest that the dissolution fluid percolates the contiguous void space almost immediately, and the HPMC-POS fibers expand isotropically as water diffuses in. Because the void space remains contiguous in isotropic expansion, the dissolution fluid continues to percolate through and diffuse into the fibers. Thus, even the densely-packed dosage forms form a low-viscosity medium that deforms and dissolves rapidly. Consequently, the solid-solution fibrous dosage forms enable enhanced release rate, supersaturation, and solubility of sparingly-soluble drugs.

The role of excipient molecular weight in drug release by fibrous dosage forms with close packing and high drug loading

In this work, the role of excipient molecular weight in drug release by close-packed, highly drug-loaded fibrous dosage forms is investigated. Three dosage forms with 87 wt% ibuprofen drug, and 13 wt% hydroxypropyl methylcellulose (HPMC) excipient of molecular weights 10, 26, and 86 kg/mol were prepared by wet 3D-patterning and drying. Upon immersion in a dissolution fluid, the dosage form with 10 kg/mol excipient fragmented and dissolved within 10 minutes. The dosage form with 26 kg/mol excipient fragmented slower, and dissolved in 60 minutes. The dosage form with 86 kg/mol excipient, however, did not fragment at all. Instead, a thick, highly viscous mass was formed that eroded slowly, in 500 minutes. Theoretical models suggest that the dissolution fluid rapidly percolates the inter-fiber void space, and a capillary pressure develops in the pores of the fibers. The fluid then diffuses into the fiber walls, and they transition to a viscous suspension. If the molecular weight of the excipient is small (~10 kg/mol), the viscosity is low and the suspension fragments and dissolves rapidly. If the molecular weight is moderate (~30 kg/mol), the fragmentation and dissolution rates are slower. If the molecular weight is large (~100 kg/mol), a thick, highly viscous mass is formed from which drug release is very slow. Thus, by appropriate choice of the molecular weight of the excipient, a wide range of drug release rates by close-packed, highly drug-loaded fibrous dosage forms can be realized.

Mechanical strength and gastric residence time of expandable fibrous dosage forms

The expandable, gastroretentive dosage forms are promising for precise control of drug concentration in blood. So far, however, short gastric retention times and safety considerations have precluded their use. In this work, to mitigate the above limitations, expandable fibrous dosage forms were investigated for mechanical strength and gastric retention time in dogs. The fiber formulation consisted of ibuprofen drug; water-absorbing, high-molecular-weight hydroxypropyl methylcellulose (HPMC) excipient; strengthening, enteric methacrylic acid-ethyl acrylate excipient; and barium sulfate, a gastrointestinal contrast agent. The fibers were coated either with a hydrophilic sugar coating, or with the strengthening enteric excipient. Upon administration to a dog, in the stomach the dosage form with sugar-coated fibers expanded to 1.7 times its initial radius in 50-100 minutes, and disintegrated after 4.8 hours. The dosage form with the enteric-excipient-coated fibers, by contrast, expanded to 1.6 times the initial radius in 5 hours. Eventually, after 31 hours the dosage form fractured due to cyclic loads applied by the contracting stomach walls. The fragments passed into the small intestine where they dissolved in less than 2-3 hours. Diametral compression tests and models of fatigue failure show that the substantial increase in gastric residence time is due to strengthening of the fibers by the enteric-excipient coating. Because the enteric excipient is a rubbery semi-solid in the acidic gastric fluid and dissolves in the pH-neutral intestinal fluids, safety concerns should be minimal. Thus, the expandable fibrous dosage forms can be designed for prolonged, safe gastric retention.

Expandable, dual-excipient fibrous dosage forms for prolonged delivery of sparingly soluble drugs

In this work, the rates of expansion and drug release by fibrous dosage forms with two excipients are investigated for prolonged delivery of sparingly soluble drugs. The formulation consisted of ibuprofen drug, high-molecular-weight hydroxypropyl methyl cellulose (HPMC) excipient, and the enteric methacrylic acid-ethyl acrylate excipient. Upon immersion in a dissolution fluid, the single fibers and all dosage forms (fiber volume fractions, φ = 0.16, 0.39, and 0.56) expanded proportional to the square-root of time, a characteristic of diffusion-controlled processes. The size of the dosage forms doubled in ten minutes, and they were converted into a highly viscous gel that was stabilized by the enteric excipient for over two days. Eighty percent of the drug was released from single fibers in less than an hour, but in thirty-eight hours from the dosage form with φ = 0.56. Theoretical models suggest that if φ is small, drug release is limited by drug diffusion through the thin fibers. But if φ is very large, drug release is determined by diffusion through the thick, viscous dosage form gel. Between these extremes the drug release time increases exponentially with φ.

Expandable fibrous dosage forms for prolonged drug delivery

Many drug therapies could be greatly improved by dosage forms that reside in the stomach for prolonged time and release the drug slowly. In this work, therefore, slow-release fibrous dosage forms that expand rapidly in the gastric fluid to prevent their passage into the intestines are investigated. The dosage forms consisted of acetaminophen drug and a high-molecular-weight hydroxypropyl methyl cellulose (HPMC) excipient. Upon immersion in a dissolution fluid, they transitioned to viscous, and expanded in proportion to the square-root of time and the reciprocal of fiber radius. The normalized axial expansion was up to 100 percent by fifteen minutes, fast enough to convert a swallowable, 10-mm diameter disk into a gastroretentive, 20-mm diameter viscous gel. The drug was released slowly, eighty percent in 2-8.4 hours. Theoretical models show that the fibrous dosage forms expand rapidly due to the fast diffusion of dissolution fluid into the thin fibers. The fibers then coalesce into a uniform viscous gel, and the diffusion length increases from the radius of the thin fibers to the half-thickness of the gelated dosage form. Consequently, drug diffusion out is slow, and the twin requirements, fast expansion and prolonged drug release, are simultaneously satisfied.

Solid-solution fibrous dosage forms for immediate delivery of sparingly-soluble drugs: Part 1. Single fibers

Solid solutions of sparingly water-soluble drugs and highly water-soluble excipients are widely used for enhancing the drug delivery rate into the blood stream. The basic physico-chemical mechanisms, however, are not well understood. To delineate the mechanisms, therefore, in this work solid-solution fibers are immersed in a small volume of dissolution fluid and the drug concentration is monitored versus time. Two formulations are considered: ibuprofen drug and low-molecular-weight hydroxypropyl methyl cellulose (HPMC) excipient; and ibuprofen and HPMC and polyoxyl stearate (POS) excipients. The fibers dissolved in the dissolution fluid and the drug was released up to three orders of magnitude faster than by ibuprofen particles, yielding a maximum supersaturation in the fluid up to 6.5 in 10-15 minutes. Past the maximum, when the fiber was fully dissolved, the drug concentration gradually decreased to terminal solubility, up to a factor of 10 greater than that of pure ibuprofen. Models suggest that the drug release rate is proportional to the drug concentration at the fiber-fluid interface, which is enhanced due to both supersaturation and solubility-increase. The interface supersaturates because the drug-molecule release rate from the fast-eroding HPMC fibers is greater than the precipitation rate within; the solubility increases proportionally to the concentration of micelle-forming POS. Similarly, the dissolution fluid supersaturates, and due to the presence of POS in the solution the terminal solubility is increased. Thus the solid-solution fibers with dual, low-molecular-weight HPMC-POS excipient enhance the release rate, supersaturation, and solubility of sparingly-soluble drugs, and their delivery rate into the blood stream.

3D-micro-patterned fibrous dosage forms for immediate drug release

At present, the most prevalent pharmaceutical dosage forms, the orally-delivered immediate-release tablets and capsules, are porous, granular solids. They disintegrate into their constituent particulates upon ingestion to release drug rapidly. The design, development, and manufacture of such granular solids, however, is inefficient due to difficulties associated with the unpredictable inter-particle interactions. Therefore, to achieve more predictable dosage form properties and processing, we have recently introduced melt-processed polymeric cellular dosage forms. The cellular forms disintegrated and released drug rapidly if the cells were predominantly interconnected. Preparation of interconnected cells, however, relies on the coalescence of gas bubbles in the melt, which is unpredictable. In the present work, therefore, new melt-processed fibrous dosage forms with contiguous void space are presented. The dosage forms are prepared by melt extrusion of the drug-excipient mixture followed by patterning the fibrous extrudate on a moving surface. It is demonstrated that the resulting fibrous structures are fully predictable by the extruder nozzle diameter and the motion of the surface. Furthermore, drug release experiments show that the disintegration time of the fibrous forms prepared in this work is of the order of that of the corresponding single fibers. The thin fibers of polyethylene glycol (excipient) and acetaminophen (drug) in turn disintegrate in a time proportional to the fiber radius and well within immediate-release specification. Finally, models of dosage form disintegration and drug release by single fibers and fibrous dosage forms are developed. It is found that drug release from fibrous forms is predictable by the physico-chemical properties of the excipient and such microstructural parameters as the fiber radius, the inter-fiber spacing, and the volume fraction of water-soluble excipient in the fibers.

Development of a portable mini-generator to safely produce nitric oxide for the treatment of infants with pulmonary hypertension

OBJECTIVES

To test the safety of a novel miniaturized device that produces nitric oxide (NO) from air by pulsed electrical discharge, and to demonstrate that the generated NO can be used to vasodilate the pulmonary vasculature in rabbits with chemically-induced pulmonary hypertension.

STUDY DESIGN

A miniature NO (mini-NO) generator was tested for its ability to produce therapeutic levels (20-80 parts per million (ppm)) of NO, while removing potentially toxic gases and metal particles. We studied healthy 6-month-old New Zealand rabbits weighing 3.4 ± 0.4 kg (mean ± SD, n = 8). Pulmonary hypertension was induced by chemically increasing right ventricular systolic pressure to 28-30 mmHg. The mini-NO generator was placed near the endotracheal tube. Production of NO was triggered by a pediatric airway flowmeter during the first 0.5 s of inspiration.

RESULTS

In rabbits with acute pulmonary hypertension, the mini-NO generator produced sufficient NO to induce pulmonary vasodilation. Potentially toxic nitrogen dioxide (NO₂) and ozone (O₃) were removed by the Ca(OH)₂ scavenger. Metallic particles, released from the electrodes by the electric plasma, were removed by a 0.22 μm filter. While producing 40 ppm NO, the mini-NO generator was cooled by a flow of air (70 ml/min) and the external temperature of the housing did not exceed 31 °C.

CONCLUSIONS

The mini-NO generator safely produced therapeutic levels of NO from air. The mini-NO generator is an effective and economical approach to producing NO for treating neonatal pulmonary hypertension and will increase the accessibility and therapeutic uses of life-saving NO therapy worldwide.

Microstructural effects in drug release by solid and cellular polymeric dosage forms: A comparative study

In recent studies, we have introduced melt-processed polymeric cellular dosage forms to achieve both immediate drug release and predictable manufacture. Dosage forms ranging from minimally-porous solids to highly porous, open-cell and thin-walled structures were prepared, and the drug release characteristics investigated as the volume fraction of cells and the excipient molecular weight were varied. In the present study, both minimally-porous solid and cellular dosage forms consisting of various weight fractions of Acetaminophen drug and polyethylene glycol (PEG) excipient are prepared and analyzed. Microstructures of the solid forms and the cell walls range from single-phase solid solutions of the excipient and a small amount of drug molecules to two-phase composites of the excipient and tightly packed drug particles. Results of dissolution experiments show that the minimally-porous solid forms disintegrate and release drug by slow surface erosion. The erosion rate decreases as the drug weight fraction is increased. By contrast, the open-cell structures disintegrate rapidly by viscous exfoliation, and the disintegration time is independent of drug weight fraction. Drug release models suggest that the solid forms erode by convective mass transfer of the faster-eroding excipient if the drug volume fraction is small. At larger drug volume fractions, however, the slower-eroding drug particles hinder access of the free-flowing fluid to the excipient, thus slowing down erosion of the composite. Conversely, the disintegration rate of the cellular forms is limited by diffusion of the dissolution fluid into the excipient phase of the thin cell walls. Because the wall thickness is of the order of the drug particle size, and the particles are enveloped by the excipient during melt-processing, the drug particles cannot hinder diffusion through the excipient across the walls. Thus the disintegration time of the cellular forms is mostly unaffected by the volume fraction of drug in the walls.

WITHDRAWN: Manufacture of Fibrous Dosage Forms by Wet Micropatterning and Drying

Available online September 18, 2017. This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Detection and removal of impurities in nitric oxide generated from air by pulsed electrical discharge

Inhalation of nitric oxide (NO) produces selective pulmonary vasodilation without dilating the systemic circulation. However, the current NO/N₂ cylinder delivery system is cumbersome and expensive. We developed a lightweight, portable, and economical device to generate NO from air by pulsed electrical discharge. The objective of this study was to investigate and optimize the purity and safety of NO generated by this device. By using low temperature streamer discharges in the plasma generator, we produced therapeutic levels of NO with very low levels of nitrogen dioxide (NO₂) and ozone. Despite the low temperature, spark generation eroded the surface of the electrodes, contaminating the gas stream with metal particles. During prolonged NO generation there was gradual loss of the iridium high-voltage tip (-90 μg/day) and the platinum-nickel ground electrode (-55 μg/day). Metal particles released from the electrodes were trapped by a high-efficiency particulate air (HEPA) filter. Quadrupole mass spectroscopy measurements of effluent gas during plasma NO generation showed that a single HEPA filter removed all of the metal particles. Mice were exposed to breathing 50 parts per million of electrically generated NO in air for 28 days with only a scavenger and no HEPA filter; the mice did not develop pulmonary inflammation or structural changes and iridium and platinum particles were not detected in the lungs of these mice. In conclusion, an electric plasma generator produced therapeutic levels of NO from air; scavenging and filtration effectively eliminated metallic impurities from the effluent gas.

Determination of the mechanical properties of solid and cellular polymeric dosage forms by diametral compression

At present, the immediate-release solid dosage forms, such as the oral tablets and capsules, are granular solids. They release drug rapidly and have adequate mechanical properties, but their manufacture is fraught with difficulties inherent in processing particulate matter. Such difficulties, however, could be overcome by liquid-based processing. Therefore, we have recently introduced polymeric cellular (i.e., highly porous) dosage forms prepared from a melt process. Experiments have shown that upon immersion in a dissolution medium, the cellular dosage forms with polyethylene glycol (PEG) as excipient and with predominantly open-cell topology disintegrate by exfoliation, thus enabling rapid drug release. If the volume fraction of voids of the open-cell structures is too large, however, their mechanical strength is adversely affected. At present, the common method for determining the tensile strength of brittle, solid dosage forms (such as select granular forms) is the diametral compression test. In this study, the theory of diametral compression is first refined to demonstrate that the relevant mechanical properties of ductile and cellular solids (i.e., the elastic modulus and the yield strength) can also be extracted from this test. Diametral compression experiments are then conducted on PEG-based solid and cellular dosage forms. It is found that the elastic modulus and yield strength of the open-cell structures are about an order of magnitude smaller than those of the non-porous solids, but still are substantially greater than the stiffness and strength requirements for handling the dosage forms manually. This work thus demonstrates that melt-processed polymeric cellular dosage forms that release drug rapidly can be designed and manufactured to have adequate mechanical properties.

On the exfoliating polymeric cellular dosage forms for immediate drug release

The most prevalent pharmaceutical dosage forms at present-the oral immediate-release tablets and capsules-are granular solids. Though effective in releasing drug rapidly, development and manufacture of such dosage forms are fraught with difficulties inherent to particulate processing. Predictable dosage form manufacture could be achieved by liquid-based processing, but cast solid dosage forms are not suitable for immediate drug release due to their resistance to fluid percolation. To overcome this limitation, we have recently introduced cellular dosage forms that can be readily prepared from polymeric melts. It has been shown that open-cell structures comprising polyethylene glycol 8000 (PEG 8k) excipient and a drug exfoliate upon immersion in a dissolution medium. The drug is then released rapidly due to the large specific surface area of the exfoliations. In this work, we vary the molecular weight of the PEG excipient and investigate its effect on the drug release kinetics of structures with predominantly open-cell topology. We demonstrate that the exfoliation rate decreases substantially if the excipient molecular weight is increased from 12 to 100kg/mol, which causes the drug dissolution time to increase by more than a factor of ten. A model is then developed to elucidate the exfoliation behavior of cellular structures. Diverse transport processes are considered: percolation due to capillarity, diffusion of dissolution medium through the cell walls, and viscous flow of the saturated excipient. It is found that the lower exfoliation rate and the longer dissolution time of the dosage forms with higher excipient molecular weight are primarily due to the greater viscosity of the cell walls after fluid penetration.

Producing nitric oxide by pulsed electrical discharge in air for portable inhalation therapy

Inhalation of nitric oxide (NO) produces selective pulmonary vasodilation and is an effective therapy for treating pulmonary hypertension in adults and children. In the United States, the average cost of 5 days of inhaled NO for persistent pulmonary hypertension of the newborn is about $14,000. NO therapy involves gas cylinders and distribution, a complex delivery device, gas monitoring and calibration equipment, and a trained respiratory therapy staff. The objective of this study was to develop a lightweight, portable device to serve as a simple and economical method of producing pure NO from air for bedside or portable use. Two NO generators were designed and tested: an offline NO generator and an inline NO generator placed directly within the inspiratory line. Both generators use pulsed electrical discharges to produce therapeutic range NO (5 to 80 parts per million) at gas flow rates of 0.5 to 5 liters/min. NO was produced from air, as well as gas mixtures containing up to 90% O2 and 10% N2. Potentially toxic gases produced in the plasma, including nitrogen dioxide (NO2) and ozone (O3), were removed using a calcium hydroxide scavenger. An iridium spark electrode produced the lowest ratio of NO2/NO. In lambs with acute pulmonary hypertension, breathing electrically generated NO produced pulmonary vasodilation and reduced pulmonary arterial pressure and pulmonary vascular resistance index. In conclusion, electrical plasma NO generation produces therapeutic levels of NO from air. After scavenging to remove NO2 and O3 and filtration to remove particles, electrically produced NO can provide safe and effective treatment of pulmonary hypertension.

Melt-processed polymeric cellular dosage forms for immediate drug release

The present immediate-release solid dosage forms, such as the oral tablets and capsules, comprise granular matrices. While effective in releasing the drug rapidly, they are fraught with difficulties inherent in processing particulate matter. By contrast, liquid-based processes would be far more predictable; but the standard cast microstructures are unsuited for immediate-release because they resist fluid percolation and penetration. In this article, we introduce cellular dosage forms that can be readily prepared from polymeric melts by incorporating the nucleation, growth, and coalescence of microscopic gas bubbles in a molding process. We show that the cell topology and formulation of such cellular structures can be engineered to reduce the length-scale of the mass-transfer step, which determines the time of drug release, from as large as the dosage form itself to as small as the thickness of the cell wall. This allows the cellular dosage forms to achieve drug release rates over an order of magnitude faster compared with those of cast matrices, spanning the entire spectrum of immediate-release and beyond. The melt-processed polymeric cellular dosage forms enable predictive design of immediate-release solid dosage forms by tailoring microstructures, and could be manufactured efficiently in a single step.