Dependence of area under the curve on proquazone particle size and in vitro dissolution rate

Characterization and evaluation in vivo of baicalin-nanocrystals prepared by an ultrasonic-homogenization-fluid bed drying method

AIM

To improve the absorption and bioavailability of baicalin using a nanocrystal (or nanosuspension) drug delivery system.

METHODS

A tandem, ultrasonic-homogenization-fluid bed drying technology was applied to prepare baicalin-nanocrystal dried powders, and the physicochemical properties of baicalin-nanocrystals were characterized by scanning electron microscopy, photon correlation spectroscopy, powder X-ray diffraction, physical stability, and solubility experiments. Furthermore, in situ intestine single-pass perfusion experiments and pharmacokinetics in rats were performed to make a comparison between the microcrystals of baicalin and pure baicalin in their absorption properties and bioavailability in vivo.

RESULTS

The mean particle size of baicalin-nanocrystals was 236 nm, with a polydispersity index of 0.173, and a zeta potential value of -34.8 mV, which provided a guarantee for the stability of the reconstituted nanosuspension. X-Ray diffraction results indicated that the crystallinity of baicalin was decreased through the ultrasonic-homogenization process. Physical stability experiments showed that the prepared baicalin-nanocrystals were sufficiently stable. It was shown that the solubility of baicalin in the form of nanocrystals, at 495 μg·mL(-1), was much higher than the baicalin-microcrystals and the physical mixture (135 and 86.4 μg·mL(-1), respectively). In situ intestine perfusion experiments demonstrated a clear advantage in the dissolution and absorption characteristics for baicalin-nanocrystals compared to the other formulations. In addition, after oral administration to rats, the particle size decrease from the micron to nanometer range exhibited much higher in vivo bioavailability (with the AUC(0-t) value of 206.96 ± 21.23 and 127.95 ± 14.41 mg·L(-1)·h(-1), respectively).

CONCLUSION

The nanocrystal drug delivery system using an ultrasonic-homogenization-fluid bed drying process is able to improve the absorption and in vivo bioavailability of baicalin, compared with pure baicalin coarse powder and micronized baicalin.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Evaluation of exposure properties after injection of nanosuspensions and microsuspenions into the intraperitoneal space in rats

In the present paper, BA99 and AC88 were used as model compounds for intraperitoneal (i.p.) administration to Sprague-Dawley rats. A major problem for the compounds, like many others newly developed pharmaceutical drugs, is the poor solubility in water. To solve solubility related problems, development of nanosuspensions is an attractive alternative. Both compounds are suitable for nanosuspensions, using the milling approach. After 2 weeks in freezer, the nanoparticles aggregated to form particles in the 400-2000 nm interval. However, following a 20 s ultrasonication step, the original particle sizes (about 200 nm) were obtained. Adding 5% mannitol before the samples were frozen abolished aggregation. It is also possible to freeze-dry the nanosuspension in the presence of 5% mannitol and re-disperse the formulation in water. Nanosuspensions of both compounds were injected i.p. to rats at 5 and 500 µmoL/kg. At the low dose, also a microsuspension was administered. I.p. administration resulted in overall improved C(max) for both AC88 and BA99 compared to s.c. and oral administration. I.p. is the preferred route of administration of tolerable drugs when a fast onset of action is desired and when a significant first passage metabolism occurs. The net charge of the active molecule appeared to affect the absorption kinetics. In the present work, the neutral molecule was favored over the negatively charged one.

New formulation approaches to improve solubility and drug release from fixed dose combinations: case examples pioglitazone/glimepiride and ezetimibe/simvastatin

Low aqueous solubility is often a limiting aspect to the bioavailability of poorly soluble, but highly permeable drugs (class II compounds according to the Biopharmaceutics Classification System - BCS) administered in single drug products or as fixed dose combinations. The aim of the present series of experiments was to improve the solubility and dissolution of two fixed dose combination formulations (FDC), each consisting of two BCS class II drugs. The first FDC contained a weak acid (glimepiride) and a weak base (pioglitazone), while the second FDC contained two compounds (simvastatin and ezetimibe) that are essentially non-ionised over the physiological pH range. The formulation approaches used were as follows: (a) an inclusion complex with hydroxypropyl-β-cyclodextrin (HP-β-CD), (b) a solid dispersion with Soluplus, a new highly water soluble polyvinyl caprolactam - polyvinyl acetate - polyethylene glycol graft copolymer and (c) a ternary inclusion complex with both HP-β-CD and Soluplus. Solid state analysis was performed for the pure drugs, and all formulations using powder X-ray diffraction (PXRD). The in vitro performance of the different formulation approaches, as gauged by solubility and dissolution experiments, was compared with that of the marketed products containing the respective fixed dose combinations, Tandemact 30 mg/4 mg tablets and Inegy 10 mg/40 mg tablets. The FDCs of the pure drugs and the marketed products showed very poor (and especially for pioglitazone, strongly pH-dependent) dissolution. By contrast, all binary and ternary inclusion complexes showed enhanced release for both drugs in the FDC. The ternary inclusion complex generated synergistic improvement in solubility and dissolution results for both FDCs. For example, in pH conditions of the fasted small intestine after a test duration of 240 min, we observed 100% dissolution of both drugs from the ternary pioglitazone/glimepiride (30 mg/4 mg) complex formulation, whereas from the marketed formulation less than 5% pioglitazone, and only 25% glimepiride dissolved. Using the same conditions, 60% ezetimibe and 85% simvastatin dissolved from the ternary ezetimibe/simvastatin (10 mg/40 mg) complex formulation, whereas with less than 5% ezetimibe and 10% simvastatin dissolved after 240 min, the marketed FDC formulation showed poor dissolution. Based on the results of the present study, the bioavailability of both drugs in the fixed dose combination is likely to be increased after oral administration of the new formulations, especially when the fixed dose combination is formulated as a ternary complex consisting of HP-β-CD and Soluplus.

Role of nanotechnology in pharmaceutical product development

A number of new molecular entities (NMEs) selected for full-scale development based on their safety and pharmacological data suffer from undesirable physicochemical and biopharmaceutical properties, which lead to poor pharmacokinetics and distribution after in vivo administration. An optimization of the preformulation studies to develop a dosage form with proper drug delivery system to achieve desirable pharmacokinetic and toxicological properties can aid in the accelerated development of these NMEs into therapies. Nanoparticulate drug delivery systems show a promising approach to obtain desirable druglike properties by altering the biopharmaceutics and pharmacokinetics properties of the molecule. Apart from the advantages of enhancing potential for systemic administration, nanoparticulate drug delivery systems can also be used for site-specific delivery, thus alleviating unwanted toxicity due to nonspecific distribution, improve patient compliance, and provide favorable clinical outcomes. This review summarizes some of the parameters and approaches that can be used to evaluate nanoparticulate drug delivery systems in early stages of formulation development.

A formulation comparison, using a solution and different nanosuspensions of a poorly soluble compound

The pharmacokinetic parameters of AZ68 administered as a solution have been compared with those from an amorphous and a crystalline nanosuspension using rats as in vivo specie. All formulations were administered intravenously (i.v.) and orally. The purpose of the study was to find out if the three different formulations were comparable and safe to administer. The results indicate that AZ68 is absorbed at a lower rate for crystalline nanosuspensions compared to amorphous nanosuspensions and solutions. However, the absorbed extent of the compound is similar. The results are a consequence of the lower solubility and the slower dissolution rate for crystalline material compared to amorphous substance in the gastrointestinal tract. The dissolution process is excluded for a solution, resulting in the fastest absorption rate. No significant difference was found between pharmacokinetic parameters when comparison was made between the formulations after i.v. administration. There were no adverse events observed after i.v. administration of the nanosuspensions.

Development of anti-influenza virus drugs I: improvement of oral absorption and in vivo anti-influenza activity of Stachyflin and its derivatives

PURPOSE

Stachyflin and its derivatives which are active against the influenza virus in vitro, were studied to improve their reduced in vivo activity after oral administration by chemical modification and some vehicles.

METHODS

The solubility was examined for different vehicles. The improvement of gastrointestinal absorption was evaluated by the plasma concentration after oral administration to mice or the in situ loop method with rats. The in vivo anti-influenza activity was examined using mice infected with the influenza virus and evaluated based on the virus titer in the lung by TCID50.

RESULTS

PEG 400 showed the highest solubility of Stachyflin and its derivative among the vehicles studied. While no viral inhibition was found in the lung after oral administration of 0.5% HPMC suspension of Stachyflin, in vivo anti-influenza virus activity was found with the PEG 400 solution. The absorption of Stachyflin by PEG 400 showed about a fifty-fold increase in AUC compared with that of 0.5% HPMC suspension. Improving the oral absorption of Stachyflin led to an increase in the in vivo anti-influenza virus activity. When the Stachyflin derivative in PEG 4000 was administered orally, there was more enhancement of the oral absorption than with PEG 400. When the aqueous solution of the phosphate ester prodrugs of Stachyflin and its derivative was administered orally, the absorption of the parent compound was improved and in vivo anti-influenza virus activity was found.

CONCLUSIONS

When Stachyflin and its derivatives were administered orally to mice with a solution in PEG and an aqueous solution of their phosphate ester, their oral absorption was improved and in vivo anti-influenza virus activity was observed.