The present study aimed to develop a practical method for preparing nanosuspension formulations of poorly water-soluble compounds for enhancing oral absorption in toxicology studies in the discovery stage. To obtain a suitable nanosuspension formulation for the intended purpose, formulations were optimized with a focus on the following characteristics: i) containing a high drug concentration, ii) consisting of commonly used excipient types in proper quantities for toxicology studies, iii) having long-term stability, and iv) having versatility for use with diverse compounds. Test compounds were milled with various excipients by wet media milling methods using a mixer mill (10 mg/batch) and a rotation/revolution mixer (0.5 g/batch). As a result, 100 mg/mL nanosuspensions of all 11 test compounds could be prepared with an optimized dispersing agent, 0.5% hydroxypropyl methylcellulose (HPMC) (3 cP)-0.5% Tween 80. Notably, it was found that the molecular weight of HPMC influenced not only particle size but also the stability of nanosuspensions and they were stable for 4 weeks at 5°C. The nanosuspensions increased in vitro dissolution rates and provided 3.9 and 3.0 times higher C max and 4.4 and 1.6 times higher area under the concentration-time curve from 0-24 h (AUC 0-24 h ) in rats (oral dose of 300 mg/kg) for cilostazol and danazol, respectively. In conclusion, applying a wet media milling method with the combination of HPMC of a small molecular weight and Tween 80 as a dispersing agent, nanosuspensions can be practically prepared and conveniently utilized for enhancing the oral absorption of poorly water-soluble compounds in toxicology studies in the discovery stage.Key words nanosuspension; toxicology study; wet media milling; mixer mill; rotation revolution mixer; oral absorptionThe proportion of poorly water-soluble compounds among drug candidates in the discovery stage has been increasing for the past decade.1,2) Because of the poor solubility of these compounds, sufficient oral absorption is not observed in animal studies, and the evaluation of pharmacological and toxicological profiles of drug candidates has therefore become more challenging. In particular, this problem frequently occurs in toxicology studies that require high oral absorption and is now a common problem in pharmaceutical companies.3)The application of formulation technologies such as solubilizing excipients, 4) solid dispersions, 5,6) and nanosuspensions 7,8) is an attractive strategy for improving oral absorption of poorly water-soluble compounds. However, the use of solubilizing excipients and solid dispersions for toxicology studies in the discovery stage is practically limited because of toxicities of excipients and amount of drug substances for formulation studies, respectively. On the other hand, nanosuspensions have the potential to solve these problems. Because nanosuspensions can be prepared as highly drug-loaded formulations with small quantities of excipients, adverse effects caused by excipients can be avoided. 9) In addition, n...
This study was conducted to investigate the use of a nanosuspension for intravenous injection into dogs to increase exposure without toxic additives for preclinical studies in the discovery stage. Nanosuspensions were prepared with a mixer mill and zirconia beads with a vehicle of 2% (w/v) poloxamer 338, which was confirmed to lead to no histamine release in dogs. Sterilized nanosuspensions of poorly water-soluble compounds, cilostazol (Cil), spironolactone (Spi) and probucol (Pro), at 10 mg ml À1 were obtained by milling for 30 min, followed by autoclaving for 20 min at 121°C and milling for 30 min (mill-autoclave-mill method). The particle sizes (d50) of Cil, Spi and Pro were 0.554, 0.484 and 0.377 μm, respectively, and the percentages of the nominal concentration were 79.1%, 99.6% and 75.4%, respectively. In chromatographic data, no extra peaks were observed. The particle size of Cil was 0.564 μm after storage for 16 days at 2-8°C. Cil in nanosuspension, but not in microsuspension, rapidly dissolved in dog plasma. Cil nanosuspension at 0.4 mg kg À1 and Cil saline solution at 0.03 mg kg À1 , around the saturation solubility, were intravenously administered to dogs. Nanosuspension increased exposure. The versatility of the mill-autoclave-mill method was checked for 15 compounds, and the particle size of 12 compounds was in the nano range. The nanosuspension optimized in this study may be useful for intravenous toxicological and pharmacological studies in the early stage of drug development.
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