Abstract
The solid dispersion technique, which is widely used in the medical field, was applied to prepare a pesticide dosage form of emamectin benzoate (EM). The preparation, physicochemical characterization, aqueous solubility, release dynamics, photolytic degradation, bioactivity, and sustained-release effects of the prepared EM solid dispersions were studied by a solvent method, using polymer materials as the carriers. Water-soluble polyvinyl pyrrolidone (PVP) K30 and water-insoluble polyacrylic resin (PR)III were used as the carriers. The influence of various parameters, such as different EM:PVP-K30 and EM:PRIII feed ratios, solvent and container choices, rotational speed and mixing time effects on pesticide loading, and the entrapment rate of the solid dispersions were investigated. The optimal conditions for the preparation of EM-PVP-K30 solid dispersions required the use of methanol and a feed ratio between 1:1 and 1:50, along with a rotational speed and mixing time of 600 rpm and 60 min, respectively. For the preparation of EM-PRIII solid dispersions, the use of methanol and a feed ratio between 1:4 and 1:50 were required, in addition to the use of a porcelain mortar for carrying out the process. Under optimized conditions, the prepared EM-PVP-K30 solid dispersions resembled potato-like, round, and irregular structures with a jagged surface. In contrast, the EM-PRIII solid dispersions were irregular solids with a microporous surface structure. The results of X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), ultraviolet (UV) spectrometry, and infrared (IR) spectrometry showed that the solid dispersions were formed by intermolecular hydrogen bonding. The solid dispersion preparation in PVP-K30 significantly improved the solubility and dissolution rate of EM, particularly the aqueous solubility, which reached a maximum of 37.5-times the EM technical solubility, when the feed ratio of 1:10 was employed to prepare the dispersion. Importantly, the wettable powder of EM-PVP-K30 solid dispersion enhanced the insecticidal activity of EM against the Plutella xylostella larvae. Furthermore, the solid dispersion preparation in PRIII afforded a significant advantage by prolonging the EM technical release in water at a pH below 7.0, especially when the PRIII content in solid dispersions was high. While the amplified toxicity of the wettable powder of EM-PRIII solid dispersions against the P. xylostella larvae showed no significant differences from that of the EM technical, the long-term toxicity under the field condition was much better than that of the commercially available EM 1.5% emulsifiable concentrate. Notably, solid dispersions with both the PVP-K30 and PRIII carriers reduced the effect of UV photolysis.
Highlights
Emamectin benzoate (EM), a biosynthetic derivative of abamectin, is a highly selective and safe insecticide and acaricide that is known for its high target selectivity and safety [1,2]
The residual solutions were kept in the constant temperature oscillation incubator that was used previously, and their EM concentrations were measured after every 60 min until the difference between two consecutive aqueous solubility measurements was less than 3%
Solid dispersion were 23.0 μg/mL, 12.3 μg/mL, and 31.3 μg/mL, respectively (Table 7). These results demonstrated that the wettable powder formed by EM-polyvinyl pyrrolidone (PVP)-K30 solid dispersion could enhance the insecticidal activity of EM technical
Summary
Emamectin benzoate (EM), a biosynthetic derivative of abamectin, is a highly selective and safe insecticide and acaricide that is known for its high target selectivity and safety [1,2]. EM is a γ-aminobutyric acid (GABA) and glutamate-gated chloride channel agonist and is highly effective against Lepidopteran, Dipteran, Homopteran, and Thrip pests [3]. Significant resistance to EM in its target pests has been observed because of the excessive and long-term use of this insecticide [4]. Its poor solubility further limits its applications. To circumvent these challenges, large quantities of adjuvants (for example, wetting agents) are typically added to the EM preparations to enhance its solubility
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