Formulation Development of Sustained-Release Microencapsulated IR3535? with Long-Duration Mosquito Repellency

Synopsis Bites from pathogen-harboring insects (e.g., mosquitos and sandflies) and noninsect arthropod pests (e.g., ticks) can result in a variety of vector-borne pathogenic diseases. Numerous commercial repellent products containing DEET, IR3535 (R) (Merck KGaA, Darmstadt, Germany), or other repellent active ingredients & mdash;but lacking sustained-release technology & mdash;are effective at repelling pests from human skin for several hours. To reduce or prevent the potential for arthropod vector-borne diseases, sustained release formulations of repellent active ingredients with long-duration benefits are needed to increase efficacy and user compliance. Here, the authors present the formulation development of a Lewis acid-Lewis base adduct encapsulated emulsion containing 20% w/w IR3535. Stability testing of the lotion was performed at ambient room temperature (20 degrees-25 degrees C) and 40 degrees C. Repellency efficacy on human subjects was tested against Aedes aegypti mosquitos in laboratory arm-in-cage studies. Anti-infective properties were assessed against multiple bacterial species. A series of sustained-release lotions of microencapsulated IR3535 was prepared. During formulation development, chemical stability was problematic. However, chemical stability was achieved by buffering the lotion with sodium citrate-citric acid. The microencapsulated formulation manifested a long -duration efficacy of 12-13 hours against A aegypti mosquitos in laboratory arm-in-cage studies. The lotion also demonstrated anti-infective properties against multiple bacterial species. This sustained release formulation achieved a long-duration efficacy benefit superior to commercial repellent products, without the unpleasant odor or oily feeling that is customary for DEET-containing products.