Potential remote drug delivery failures due to temperature-dependent viscosity and drug-loss of aqueous and emulsion-based fluids

Abstract

The ability to inject wild animals from a distance using remote drug delivery systems (RDDS) is one of the most effective and humane practices in wildlife management. Several factors affect the successful administration of drugs using RDDS. For example, temperature-dependent viscosity change in aqueous (Newtonian) or water-in-oil emulsion (non-Newtonian) fluids, commonly used in tranquilizer and adjuvant-based vaccines, respectively, can potentially result in drug delivery failure. To better understand impacts due to viscosity changes, we investigated the fluid dynamics and ballistics involved in remote drug delivery. Our research was divided into two phases: we investigated the viscosimetric physics in the first phase to determine the fluid behavior under different temperature settings, simulating recommended storage temperature (7°C), plus an ambient temperature (20°C). In the second phase of our study, we assessed the drug delivery efficiency by specialized darts, using a precision CO2 projector and a blowgun. Efficiency assessment was done by comparing the original drug volume with the actual volume injected after firing the dart into a fresh pork hide mounted on a ballistic gel. Before testing, we configured the required minimum impact velocity as our parameter for intramuscular injection (determined as > 40 m/sec). All executed dart-deployments performed satisfactorily, despite initial concerns of potential incomplete drug delivery, however, noteworthy drug loss was observed (>10%) associated with drug residues in syringe/dart dead space and within the transfer needle. This could potentially result in inaccurate dosing depending on the drug used. Furthermore, the use of a blowgun for remote drug delivery (>3m) is discouraged, especially when using specialized darts, as the required minimum dart velocity for adequate penetration is difficult to reach, in addition to a loss of precision during targeting.