Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 February 2021 | 13(2): 17639–17645
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
https://doi.org/10.11609/jott.5745.13.2.17639-17645
#5745 | Received 30 January 2020 | Final
received 06 February 2021 | Finally accepted 16 February 2021
Potential remote drug delivery
failures due to temperature-dependent viscosity and drug-loss of aqueous and
emulsion-based fluids
Derek Andrew Rosenfield 1,
Alfredo Acosta 2, Denise Trigilio Tavares
3 & Cristiane Schilbach Pizzutto 4
1,4 Department of Animal
Reproduction, Faculty of Veterinary Medicine and Animal Science, University of Sao Paulo, SP 05508-270,
Brazil.
2 Department of
Preventive Veterinary Medicine and Animal Health, Experimental Epidemiology Applied to
Zoonosis, Faculty of Veterinary Medicine and Animal Science, University of Sao
Paulo, SP 05508-270, Brazil.
3 Department of
Chemical Engineering, Polytechnic School, University of Sao Paulo, SP
05508-270, Brazil.
1 dro@usp.br
(corresponding author), 2 alfredoacosta@usp.br, 3 denise.tavares@usp.br,
4 crissp@usp.br
Editor: Aniruddha Belsare, Michigan State University, East Lansing, USA. Date
of publication: 26 February 2021 (online & print)
Citation: Rosenfield, D.A., A. Acosta, D.T. Tavares & C.S. Pizzutto (2021). Potential remote drug delivery failures due to
temperature-dependent viscosity and drug-loss of aqueous and emulsion-based
fluids. Journal of Threatened Taxa 13(2): 17639–17645. https://doi.org/10.11609/jott.5745.13.2.17639-17645
Copyright: © Rosenfield et al. 2021. Creative
Commons Attribution 4.0 International License.
JoTT allows unrestricted use, reproduction,
and distribution of this article in any medium by providing adequate credit to
the author(s) and the source of publication.
Funding: We thank the Pneu-Dart, Inc.,
Williamsport, Pennsylvania, for their
cooperation and material contributions. The project was partially
funded by FAPESP, Sao
Paulo, Brazil. Project Number 2016/12549-5.
Competing interests: The authors declare no competing interests.
Author details: Derek Andrew Rosenfield (DVM; MSc; DSc) is a post-graduate researcher at the
Department of Animal Reproduction (Wildlife), Faculty of Veterinary Medicine
and Animal Science (FMVZ), University of Sao Paulo (USP), Brazil. His research
focuses on wildlife population control to mitigate human-wildlife conflicts and
zoonotic disease transmission, through reversible contraceptive methods, with
emphasis on immunocontraception. Alfredo Acosta, graduated as
agricultural engineer, and currently pursuing his doctorate at the Department
of Preventive Veterinary Medicine and Animal Health, Faculty of Veterinary
Medicine and Animal Science, University of São Paulo. Experience in
epidemiology and preventive veterinary medicine, with an emphasis on Animal
Health. Denise
Trigilio Tavares (MSc) Department of Chemical
Engineering, Polytechnic School, University of Sao Paulo. Graduated in
Chemistry and in Environmental Technology. She
currently works as a laboratory technician at the Department of Chemical
Engineering at the Polytechnic School of the University of São Paulo, with an
emphasis on the area of Petroleum Derivatives and Thermal and Mechanical
Separations. Cristiane Schilbach Pizzutto
is a professor and research supervisor at the Department of Animal
Reproduction, Faculty of Veterinary Medicine and Animal Science (FMVZ),
University of Sao Paulo (USP), Brazil. In addition, her research focuses on
animal wellbeing through environmental enrichment, supported by her role as
President of the Animal Welfare Committee, at the State Board of Veterinary
Medicine, SP, and Member of the International Environmental Enrichment
Conference Committee.
Author contributions: DAR—conceived the work, designed, and conducted the
field surveys, data collection, and analysis. Wrote the manuscript.
AA—conducted data analysis. Spanish context.
DTT—conducted lab work and analysis. CSP—contributed to manuscript and
data analysis.
Acknowledgements: The project was partially funded by the Sao Paulo
Research Foundation (FAPESP), doctoral scholarship - grant number 2016/12549-5
and by Pneu-Dart, Inc., Williamsport, PA, USA,
providing equipment and material.
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 (7ºC), plus an
ambient temperature (20ºC). 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.
Keywords: Ballistic, darts, inject,
immunogenic, remote drug delivery system, tranquilizer, vaccines, wildlife.
Abbreviations: RH—Efficiency assessment of
remote drug delivery systems.
Spanish Resumen:
La habilidad para inyectar animales salvajes a distancia,
utilizando sistemas de administración remota de
medicamentos (RDDS), es una de las más efectivas y humanizadas prácticas
en el manejo de la vida silvestre. Varios factores afectan la administración exitosa de
medicamentos usando RDDS. Por ejemplo, el cambio de viscosidad, dependiente de la temperatura en fluidos acuosos (newtonianos)
o las emulsiones de agua en
aceite (no newtonianos), comúnmente usados en tranquilizantes y en vacunas con base de adyuvantes; estos cambios pueden
potencialmente resultar en fallas
en la administración
de los fármacos. Para comprender
mejor los impactos debidos a los cambios
de viscosidad, investigamos la
dinámica de fluidos y balística involucrados en la administración
remota de fármacos. Nuestra investigación
se dividió en dos fases: en la primera
fase investigamos la física viscosimétrica para
determinar el comportamiento
del fluido a diferentes niveles de temperatura,
simulando la temperatura de almacenamiento
recomendada (7ºC), además de una temperatura ambiente
(20ºC); en la segunda fase,
evaluamos la eficacia de la administración de fármacos mediante dardos especializados
utilizando un rifle de precisión
de CO2 y una cerbatana. Se realizó
una evaluación de la eficiencia comparando el volumen de fármaco original con el volumen real inyectado después de disparar el dardo en una piel de cerdo fresca montada en un gel balístico. Antes de la prueba, configuramos la velocidad de impacto mínima requerida para nuestros parámetros y la inyección intramuscular
(determinada como ˃ 40 m/s). Todos los despliegues de dardos se comportaron
satisfactoriamente, a pesar de las
preocupaciones iniciales de
una posible entrega incompleta del
fármaco. Sin embargo, se observó
una pérdida de fármaco notable
(~ 10%) asociada al residuo
de fármaco en el espacio muerto de la jeringa / dardo y dentro de la aguja de transferencia.
Esto podría potencialmente
resultar en una dosificación
inexacta dependiendo del medicamento utilizado. Por otra
parte, el uso de la cerbatana para administración
remota de medicamentos (> 3 m) es desaconsejada,
especialmente cuando se utilizan
dardos especializados, debido a que la velocidad mínima requerida
para una penetración adecuada
es difícil de alcanzar, además
de la pérdida de precisión al apuntar.
Palabras clave: balístico, dardos, inyectable, inmunogénico, sistema
de administración remota de fármacos, tranquilizante,
vacunas, vida silvestre.
Introduction
The ability to inject wild animals from a distance
without the need for physical restraint has many advantages, including
logistics, safety, and improved animal welfare.
Several factors, however, influence the success of drug delivery using a
remote drug delivery system (RDDS), including the user’s ability to accurately
use RDDS (Cattet et al. 2006), ambient influences
(weather/light), dart ballistics, and drug solution characteristics. The drug’s specific fluid characteristics can
potentially interfere with the delivery efficiency when used in a dart and can
be easily overlooked, especially when it comes to temperature-dependent
viscosity (Evans et al. 2015). This is
an important issue for wildlife vaccines.
Vaccines developed for wildlife applications have to be highly
immunogenic, thus permitting a single dose application. The duration of immunity after vaccination
should also last long. Water-in-oil
emulsions and adjuvants provide such attributes, but depending on temperature,
the emulsion’s viscosity (fluid resistance) can be a hindrance if remote drug
delivery is to be used for vaccine delivery.
RDDS technologies have progressed significantly in
recent times, allowing for specific application needs. For example, a vaccine with the
aforementioned characteristics has to be injected as a bolus (depot),
subcutaneously or intramuscularly. This
can be accomplished with a single-port cannula dart. On the other hand, a tranquilizer drug is
delivered using a dart with a tri-port cannula that injects the drug over a
large area in a dispersed fashion, facilitating quicker drug absorption for
faster biological effects.
The work described in this paper was motivated by an
experience during our immunocontraception project for wildlife population
control. While administering the immunocontraceptive vaccine stored at 4–7 ºC
intramuscularly by a hand syringe, a substantial manual force was required even
with a large diameter cannula (18 gauge).
We were, therefore, concerned about potential delivery failure or incomplete
delivery with RDDS. A potential solution
was to increase the temperature of the vaccine to ambient temperature before
deployment. This study aimed to assess
the impact of temperature on the delivery of a solution while using RDDS. Although there are several publications on the
use of darts in wildlife (Kreeger 1997; Cattet et al. 2006; Cracknell 2013; Evans et al. 2015;
Griffin 2015; McCaan et al. 2017; Rosenfield 2017),
to our best knowledge, none addressed the fluid dynamics and efficiency of drug
delivery. Furthermore, we investigated
if specialized darts for vaccine delivery can be adequately deployed by
blowguns.
Objectives
1) To assess temperature-dependent viscosity dynamics
of aqueous and emulsion solution by comparing Newtonian (aqueous) and
non-Newtonian (emulsion) fluid behavior under the
influence of temperature variance on their viscosity dynamics.
2) To determine
minimum impact velocity and dart delivery ballistics by classifying the minimum
impact velocity (MIV) necessary for adequate dart penetration, to minimize
potential tissue damage using:
CO2 projector (20m)
Blowgun (3m)
3) To evaluate
drug delivery efficiency of aqueous and emulsion-based solutions at two
different temperature conditions (storage 7ºC; ambient 20ºC), by comparing
weights of the syringe, transfer needle, dart, and dart cannula before and
after use/deployment to identify any potential drug volume loss.
Materials & Methods
Experimental design for fluid behavior
of emulsion and aqueous solution:
To determine the impact of temperature on the
viscosity of aqueous and emulsion-based fluids, as typically found in
injectable anesthetics and vaccines, we used the
programmable Rheometer, Brookfield DV-III, a cone plate version viscometer, and
the Waele’s Ostwald equation:
whereby:
• K (flow consistency index) expressed in (N/m ^ 2).
(Sn)
• n (flow behavior index),
dimensionless.
• du / dy (shear rate),
expressed in 1/s.
Water-in-oil emulsion (non-Newtonian fluid)
We analyzed the temperature
impact on the viscosity of an injectable, water-in-oil based emulsion. We used an original sham vaccine (USDA, NWRC,
Fort Collins, USA) at two temperature settings.
First, simulating the manufacturer’s recommended storage temperature of
7ºC, and second, at an ambient temperature of 20ºC. The temperature of the tested fluid was
maintained by using the Rheometer’s temperature-controlled circulating
bath. Subsequently, the viscosity was
measured with different spindle sizes and rotation velocities. Each test was then repeated.
Aqueous solution (Newtonian fluid)
For comparison, we also tested an aqueous-based fluid,
simulating a drug consistency commonly found in tranquilizer drugs by preparing
a saline/ethylene glycol solution (90% v/v to 10% v/v). The viscosity tests were performed at
20ºC. Subsequently, the viscosity was
measured with different spindle sizes and rotation velocities. Each test was then repeated.
Statistics
To evaluate the differences between the means for
viscosity samples, a bi-caudal Welch’s t-test was used considering unequal
sample sizes. The data was analyzed using Stats Package (Version 3.6.2) in R (R Core
Team 2020).
Dart-delivery assessment
Equipment
CO2 Projector: Distance darting was
performed using a high-precision CO2 projector (X-Caliber, 50 cal. [12.3mm] Pneu-Dart,
Inc., Williamsport, PA, USA) with a mounted scope.
Blowgun: For the blowgun tests, we used a 58.5cm
length blowgun, with a 12.3mm diameter (Pneu-Dart,
Inc.).
Darts (n=6): The employed dart specifications: Type P,
cannula length 31,75mm, gel collar, single-port, and a tri-port, with an
explosive charge.
Chronographer: Dart-velocity recording was performed
by using a precision chronographer, recorded in m/sec (accuracy +/- 0.25%),
along with external digital data recording (Ballistic Precision Speed
Chronograph, Caldwell, USA). The
chronographer was placed 30cm in front of the target field. The darts were fired in such a way, that they
pass two screens, and the time it takes for the darts to travel the distance
between the screens is measured electronically.
Target: The target was a 112mm thick piece of fresh
pigskin with an intact layer of adipose tissue and some visible areas of
connected muscular tissue, serving as an indicator for intramuscular (IM)
injection (Image 1). The pigskin was
mounted onto a block of 10% ballistic gel.
Basic set-up - Distance darting: The CO2
projector was mounted on a rifle shooting rests (Caldwell, USA), with the scope
zeroed-in at a distance of 20m.
Shooting execution: Using the manufacturer’s
guidelines for initial pressure settings on the CO2 projector, we
developed our own settings, designated as “minimum impact velocity” (MIV). Most common dart delivery-failures are due to
inadequate pressure settings on the CO2 projector. Too low of a pressure and the dart will not
reach their intended targets or bounce off the animal. Too high of a pressure, and the dart may
provoke extensive tissue injury or ricochet.
MIV refers to the lowest functional pressure setting, allowing for the
dart to reach its target with adequate intramuscular penetration, believed to
minimize tissue damage. Optimal depth was considered when the dart’s gel collar
was positioned on the far side of the pork skin’s adipose tissue, allowing for
the cannula orifice to reach muscle tissue.
This was accomplished by gradually increasing the gas pressure and recording
the dart’s velocity. The results were
quantified by needle penetration depth:
* Full =
gel collar past skin/fat layer
* ½ = gel
collar stuck within the skin/fat layer
* F =
failure of gel collar to penetrate the skin
The setting with the lowest pressure that resulted in
full penetration was used as the new MIV.
Basic set-up - Blowgun
Darting via blowgun was performed from a distance of
3m, using the same chronograph setup to assess minimum impact velocity.
Assessment of Drug Delivery Efficiency
Before testing, all syringes, transfer needles, and
darts were identified with permanent markers.
The efficiency of drug delivery was determined by the weight-differences
between:
1) original quantity (1mL) of the sham vaccine,
prefilled in 3mL syringes (Henke-Sass, Wolf GmbH, Germany)
2) 18G x 76.2mm transfer needle (Pneu-Dart,
Inc.), before and after use
3) Dart empty weight
4) Full-filled dart weight (dart + drug load) prior to
deployment
5) Dart weight after deployment (drug injected into
the target)
Weight differences were determined by using a digital
precision top scale (500g x 0.01g).
The difference in weight between the original sham
vaccine-loaded syringe and the weight of the vaccine-filled dart after
deployment was considered the net drug weight deposited. Any weight difference not being equal to the
1mL sham vaccine weight was considered to be the amount of drug lost.
RESULTS
Fluid behavior
Water-in-oil emulsion (non-Newtonian fluid)
The rheological behavior of
the sham vaccine, a water-in-oil emulsion, indicated that there is no linear
relationship between tension and strain rate.
It is, therefore, a liquid with non-Newtonian behavior. As for the temperature, it was observed that
the increase in temperature implies a greater fluidity of the emulsion, a behavior that is typical of viscous liquids (Fig.1). The emulsion’s viscosity was significantly
different at two different temperatures, 7ºC vs. 20ºC (Bi-caudal Welch’s t-test
[p=0.04052;95% CI, 598.00–20160.65]).
Aqueous Solution (Newtonian fluid)
The aqueous solution presented a linear relationship
between the stress and the rate of deformation, i.e. Newtonian behavior. Therefore,
the viscosity of the aqueous solution can be defined as being constant at a
temperatures of 7ºC, and constant at a temperature of 20ºC, however,
significantly different when compared to one another, (viscosity cP 8 to cP 2, respectively),
(Fig. 2) (Bi-caudal Welch’s t-test [p=0.0000156; 95% CI,-7.634565/-5.850435]).
Minimum impact velocity
For our specific equipment, the pre-determined impact
velocity necessary for adequate dart cannula penetration to reach intramuscular
tissue was ≥ 40m/s. As demonstrated in
Images 1 & 2, the identified MIV allowed all deployed darts to reach IM
injection depth.
Overall drug delivery quality
Not considering drug volume loss due to
cannula/syringe/dart dead-space, the drug volume deposited of all deployed
darts were satisfactorily (Image 3).
Images 4 A and B demonstrate the different deposit characteristics with
a single-port and a tri-port cannula, respectively.
Dart weight-differences
We identified a mean drug weight difference between
original drug volume (1mL pre-deployment) and injected volume (0.886mL)
post-deployment). The weight difference of 0.114gm was statistically
significant (p<0.01; 95% CI, 0.076–0.123).
Weight Difference of deposited drug volume by
temperature variations:
Differences in deposited drug volume due to
temperature variant (7°C vs. 20°C) were considered statistically not
significant (p=0.3194).
Drug Volume Loss
The only significant drug loss identified was related
to the residue in the transfer needle in addition to the residue in the syringe
hub (dead space), (Image 5), a space
between the syringe needle and barrel.
Hypothesized drug loss using dead space’s volume
calculations for transfer syringe/needle and dart/canula
Formula: V = πr2h
Where the 18G syringe needle volume (dead space) =
0.84 mm ID x 76.2 mm length.
V = 4.22mm³ = 0.00422mL
Where the 14G Dart cannula = 1.6mm ID x 31.75mm
V = 67.06mm³ = 0.06706mL
Total syringe needle/dart canula residue volume:
0.07128mL
Also, prior identified dead space of conventional 1mL
syringes (Küme et al. 2012; UC Davis 2016) of
0.066mL, including the same volume amount for the dart hub, the total hub
volume projected is 0.132mL. Adding the calculated syringe/cannula and the hub
dead space, the total residue volume could be as high as 0.203mL, a potential
20% drug loss.
DISCUSSION
The initial concern due to the potential increase in
fluid resistance for an emulsion-based drug stored at 7ºC was
corroborated during the viscosity assessment, where temperature-dependent
rheological behavior was evident. Similar concerns were reported by Baker et
al. (2005) and Kirkpatrick et al. (2011), when observing delivery failure,
potentially linked to the viscosity issue of a polymer mixture. Our experiment results confirmed a
significant temperature impact on emulsion-based fluids. Specifically, that a decrease in solution temperature
increases fluid resistance (Palm et al. 2015).
Although drug delivery using darts was efficient for
fluids at 7ºC as well as 20, as observed in our pork skin/ballistic gel setup,
attention should be paid to other potential delivery failures when darting live
animal, in particular, due to drug fluids traveling back the wound channel, as
described by (Evans et al. 2015). The
use of a blow-gun is discouraged as the indicated minimum impact velocity of
specialized darts for adequate perforation would be difficult to achieve,
leading to inadequate injection depth, failure to trigger propellent mechanism
or bounce-backs.
Finally, drug loss due to accumulated residue in the
syringe and dart dead spaces, dart cannula and transfer needle should be
considered when using drugs sensitive to minute variations. To the best of our knowledge, scientific
literature on potential drug loss due to dead-space in darts does not exist,
however, similar corroborated information can be found in human medicine (Bobashev & Zule 2010; UC
Davis, YSP, 2016).
CONCLUSION
Contrary to our initial concerns, the findings of this
study demonstrated efficient drug deliveries, without the need to warm an
emulsion-based vaccine to ambient temperatures.
Nevertheless, the drug volume loss attributed to dead-space residues of
the syringe, needle, dart during drug transfer from the syringe to dart, is
noteworthy. Drug delivery with
specialized darts, using any kind of propellant, will bring about tissue
damages to a certain degree. But risks
associated with physical restraint (nets, traps, etc.) are much greater. Remote drug delivery systems, with their high
precision, reliability of drug delivery, and safety for animals and personnel,
may outweigh the potential adverse effects.
Overall, our results suggest that RDDS can be used for emulsion-based
drug delivery.
For figures
& images - - click here
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