Characterisation of Pheroid® formulations with specific reference to azoxystrobin

Abstract

The aim of this project was to set standardized specifications for anti-infective Pheroid® products that would ultimately promote quality control and the reproducibility of formulations. Background and rationale Standard specifications are a set of evaluations, references to analytical processes and acceptance criteria that are converted into the numerical ranges that provide the outline of a product. An acceptable product abides by these ranges as it serves as the most important regulatory measures. The Pheroid® delivery system is a colloidal delivery system that comprises of a unique submicron type of formulation that is environmentally safe and contains non-toxic ingredients. The system has successfully been applied in several applications and has been shown to provide promising results – especially in anti-infective formulations, some of the most commonly used agents in the world. During this study, it was sought to describe and formalize existing ranges for anti-infective Pheroid® products that would ultimately promote quality control and the reproducibility of formulations. The results would then be verified through the formulation of the fungicide, azoxystrobin, in the Pheroid® delivery system according to the determined ranges. The use of a plant model to verify the formalized ranges is effective and much less time consuming than an animal or human model. To achieve the stated aim, data was collected from previously manufactured anti-infective Pheroid® formulations, grouped according to the type of Pheroid® used and subdivided according to the variables in the formulations (e.g. active ingredient or additives). The data was subsequently statistically analysed with regards to the characterization results that were obtained for the various formulations (i.e. confocal laser scanning microscopy, Mastersize analysis, and zeta potential measurements). Unfortunately, due to insufficient data and the unpredictable behaviour observed with several formulations, the establishment of specification ranges was not feasible and the aim could not be met. The azoxystrobin/Pheroid® formulation could not be compiled with the use of the formalized ranges as intended but was manufactured nonetheless through solubility testing. In addition, an insecticide, chlorpyrifos, was also manufactured using Pheroid® technology. Results Two azoxystrobin/pro-Pheroid® formulations (6.25% and 12.5% in turn) were manufactured and tested for their efficacy and possible phytotoxicity against late blight (Phytophthora infestans) on tomatoes and white blister (Albugo candida) on cabbage. Relative to the control, the comparator (0.15 μm /mL) was slightly more effective than the same-strength azoxystrobin/pro-Pheroid® formulations (71.64% compared to equal effectiveness of 70.15%) against late blight on tomatoes. In the control of white blister on cabbage, the comparator (0.94 μm /mL) was more effective than the double strength azoxystrobin/pro-Pheroid® formulations and significantly more effective than the same-strength azoxystrobin/pro-Pheroid® formulations relative to the control. The efficacy and possible phytotoxicity of the chlorpyrifos/pro-Pheroid® formulation were tested against African Bollworm (Helicoverpa armigera) on tomatoes and cabbage aphids (Brevicoryne brassicae). In the control of African bollworm in tomatoes, half the standard strength chlorpyrifos/pro-Pheroid® (0.36 μg /mL) was 15.3% more effective than the comparator (0.72 μg /mL). At the same strength than the comparator (0.24 μg /mL), it was 14.9% more effective in controlling cabbage aphids than the comparator. Conclusion The incorporation of the two anti-infective compounds, azoxystrobin (fungicide) and chlorpyrifos (insecticide) in Pheroid® technology was not equally successful. The azoxystrobin/pro-Pheroid® formulations did not provide increased efficacy compared to the comparator whereas the chlorpyrifos/pro-Pheroid® formulation delivered results that were superior to the comparators in the control of late blight on tomatoes (at half the concentration) as well as white blister on cabbage (at the same concentration). Pheroid® technology’s potential in the agricultural industry (with specific reference to anti-infective application) was observed in the chlorpyrifos/pro-Pheroid® formulation; therefore, it was concluded that the solubility studies for the azoxystrobin/pro-Pheroid® formulations should be revisited in the near future.