Expandable fibrous dosage forms for prolonged drug delivery

Gastroretentive fibrous dosage forms for prolonged delivery of sparingly-soluble tyrosine kinase inhibitors. Part 1: Dosage form design, and models of expansion, post-expansion mechanical strength, and drug release

At present, the efficacy and safety of many cancer therapies employing a sparingly-soluble tyrosine kinase inhibitor (TKI) are compromised by excessive fluctuations in the drug concentration in blood. To mitigate this limitation, in this four-part study expandable, gastroretentive fibrous dosage forms that deliver drug into the gastric fluid (and into the blood) at a controlled rate for prolonged time are presented. The dosage form comprises a cross-ply structure of water-absorbing, high-molecular-weight hydroxypropyl methylcellulose (HPMC) based fibers coated with a strengthening, enteric excipient. The intervening spaces between the coated fibers are solid annuli of dispersed drug particles in a low-molecular-weight HPMC-based excipient matrix. The central regions of the annuli are open channels. In this part, models are developed for dosage form expansion, post-expansion mechanical strength, and drug release. The models suggest that upon immersing in a dissolution fluid, the fluid percolates the open channels, diffuses into the annuli and the coated fibers, and the dosage form expands. The expansion rate is inversely proportional, and the post-expansion mechanical strength proportional to the volume fraction of the coating. Drug particles are released from the annuli as the surrounding excipient dissolves. The drug release rate is proportional to the concentration of low-molecular-weight HPMC at the annulus/dissolution fluid interface. The dosage forms can be readily designed for expansion in a few hours, formation of a high-strength viscoelastic mass, and drug release at a constant rate over a day.

Gastroretentive fibrous dosage forms for prolonged delivery of sparingly-soluble tyrosine kinase inhibitors. Part 2: Experimental validation of the models of expansion, post-expansion mechanical strength, and drug release

In Part 1, we have introduced expandable gastroretentive fibrous dosage forms for prolonged delivery of sparingly-soluble tyrosine kinase inhibitors. The expansion rate, post-expansion mechanical strength, and drug release rate were modeled for a dosage form containing 200 mg nilotinib. In the present part, the dosage form was prepared and tested in vitro to validate the models. Upon immersing in a dissolution fluid, the fibrous dosage form expanded at a constant rate to a normalized radial expansion of 0.5 by 4 hours, and then formed an expanded viscoelastic mass of high strength. The drug was released at a constant rate over a day. For comparison, a particle-filled gelatin capsule with the same amount of nilotinib disintegrated almost immediately, and released eighty percent of the drug content in just 10 minutes. The experimental data validate the theoretical models of Part 1 reasonably.

Gastroretentive fibrous dosage forms for prolonged delivery of sparingly-soluble tyrosine kinase inhibitors. Part 4: Experimental validation of the models of drug concentration in blood

In this final part, the models of drug concentration in blood developed in Part 3 are validated on dogs. Both slow-release gastroretentive fibrous and immediate-release particulate dosage forms containing 200 mg nilotinib were tested. After administering, the fibrous dosage form expanded linearly with time in the stomach, to about 1.5 times the initial radius by 4 h. The expanded dosage form fractured after 10 h, and then passed into the intestines. The drug concentration in blood exhibited a broad peak with a maximum of 0.51 μg/ml and a width at half-height of 10.2 h. By contrast, after administering the immediate-release capsule the drug concentration in blood exhibited a sharp peak with a maximum of 0.68 μg/ml and a width at half-height of just 3.6 h. The experimental data validate the theoretical models reasonably. The gastroretentive fibrous dosage forms designed in this study enable a steady drug concentration in blood for increasing the efficacy and mitigating side effects of drug therapies.

Design and evaluation of gastro-swelling/gastro-floating sustained-release tablets of brivaracetam for epilepsy therapy

To prolong the absorption of the drug and achieve the effect of gastric retention, new brivaracetam tablets together with the characteristics of rapid swelling and sustained floating have been developed here. The tablets were optimized and prepared by direct compression techniques using Kollidon® SR and cross-linked polyvinylpyrrolidone (PVPP) XL as the matrix and disintegrant respectively, and carbomer 71G NF and polyethylene oxide (PEO) N60K as the gel materials to achieve sustained release effect. The characteristics of static expansion, floating time, drug release and dynamic swelling performance in vitro of the tablets were evaluated. The optimized formulations (F5 and F10) exhibited satisfactory swelling and floating properties, mechanical strength, and in vitro sustained-release characteristic with diffusion and matrix erosion mechanisms. X-ray images of beagle dogs showed that the tablet F5 could be retained in the stomach for more than 6 h. Furthermore, the pharmacokinetic studies in volunteers exhibited that the bioavailability of F5 and F10 was 95.70% (90% CI, 83.80%-109.28%) and 103.39% (90% CI, 87.61%-122.01%), respectively, relative to commercial tablets, with Tmax prolonged, demonstrating an excellent sustained-release effect. Therefore, the present system can reduce dosing frequency and improve patient compliance, which is expected to be a promising treatment option for epilepsy patients.

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.

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.

A pH-sensitive, stimuli-responsive, superabsorbent, smart hydrogel from psyllium (Plantago ovata) for intelligent drug delivery

Herein, we report a polysaccharide-based hydrogel isolated from psyllium husk (a well-known dietary fiber) and evaluated for its swelling properties in deionized water (DW) at different physiological pH values, i.e., 1.2, 6.8 and 7.4. Swelling of psyllium hydrogel (PSH) in DW under the influence of temperature and at different concentrations of NaCl and KCl solutions was also examined. A pH-dependent swelling pattern of PSH was observed following the order DW > pH 7.4 > pH 6.8 > pH 1.2. Stimuli-responsive swelling and deswelling (on-off switching) behavior of PSH was observed in DW and ethanol, DW and normal saline, at pH 7.4 and pH 1.2 environments, respectively. Similar swelling behavior and on-off switching attribute of PSH-containing tablets indicated the unaltered nature of PSH even after compression. Scanning electron micrographs of swollen and then freeze-dried PSH via transverse and longitudinal cross-sections revealed hollow channels with an average pore size of 6 ± 2 μm. Furthermore, PSH concentration-dependent sustained release of theophylline from tablet formulation was witnessed for >15 h following the non-Fickian diffusion mechanism. Subacute toxicity studies revealed the non-toxic nature of PSH. Therefore, dietary fiber-based material, i.e., PSH could be a valuable pharmaceutical excipient for intelligent and targeted drug delivery.

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.