master.on
New Member
Stability of cabergoline in fox baits in laboratory and field conditions
Abstract
Cabergoline is a potent inhibitor of prolactin release and a potential fertility control agent for foxes. To understand how cabergoline could behave in baits deployed for fox control, we conducted laboratory and field trials to investigate the stability of cabergoline when ( 1) in solution, ( 2) injected into a bait ( deep- fried liver and Foxoff (R)) and ( 3) exposed to a range of environmental conditions, including burial. Cabergoline, dissolved in a 1% acetic acid solution, and its carboxylic acid hydrolysis product can be assayed using high- performance liquid chromatography. When stored at 4 degrees C and at room temperature, cabergoline in solution was stable for up to 36 days. When stored under cool (<= 15 degrees C), dry conditions, cabergoline ( 800 mu g) in commercial Foxoff (R) and deep- fried ox-liver baits was stable for 28 and 7 days, respectively; stability was reduced by increases in temperature ( tested up to 40 degrees C) and humidity. Recovery of cabergoline from buried baits exposed to a range of field conditions decreased rapidly in the first week, but after 56 days remained detectable at levels of 6 - 22% of the injected amounts. This study has important implications for baiting campaigns that use cabergoline for fox control.
(PDF Download Available). Available from:
Stability of cabergoline in fox baits in laboratory and field conditions (PDF Download Available)
Stability of cabergoline in solution
The stability of cabergoline in solution on storage was determined
with a solution of 1 mg mL–1 divided into ten 1-mL
aliquots placed into 1.5 mL Teflon septum-sealed, screw-capped
glass vials. The vials were kept at 4°C (n = 5) or 10–15°C
(ambient temperature) (n = 5) and analysed after 0, 7, 14 and
36 days. To investigate long-term stability in solution, we
assessed the concentration of cabergoline (1 mg mL–1 in 1%
acetic acid) after 14 months storage at 4°C. For analysis, 40 µL
were removed and diluted to 1 mL with 1% acetic acid, and
20 µL of this solution (nominally containing 800 ng cabergoline)
was injected into the HPLC.
To study the effect of pH on the stability of cabergoline,
80 µL of 1 mg mL–1 1% acetic acid were diluted to 2 mL with
distilled water or buffers of pH 7, 8 or 9. Phosphate buffer
(0.067 M) was used for pH 7 and 8, and carbonate buffer (0.1 M)
for pH 9. After incubation at 60°C (high temperature was used
to increase the rate of break down) for up to 120 min, 200-µL
aliquots were removed, acidified with 50 µL 0.25 M HCl, and
analysed by HPLC.
Results
Stability of cabergoline in solution
Calibration curves were prepared daily by dilution of the
primary solution of cabergoline with 1% acetic acid. The curves
showed excellent linearity over the range 10–1600 ng injected in
20 µL. However, curves were usually prepared over a smaller
range (10–800 ng) to suit the needs of the stability studies
(Fig. 1). The lower limit of quantification was taken to be the
lowest point (10 ng) on the curve. There was no loss of cabergoline
from solutions in 1% acetic acid when stored in the
refrigerator at 4°C or at room temperature for up to 36 days.
After 14 months’ storage at 4°C, however, the concentration of
cabergoline in solution had fallen by 50%.
When heated with base (pH 8 or 9), cabergoline disappeared
over time and was replaced by another peak that eluted just
before it (Fig. 2). HPLC-MS analysis confirmed that the caber
goline peak gave a characteristic [M + H+] ion at m/z 452, while
the earlier peak give an [M + H+] ion at m/z 297, and was the
carboxylic acid breakdown product (cab acid), formed by
hydrolysis of the acylurea bond in the cabergoline. The rate of
decomposition of cabergoline increased with increasing pH
(Fig. 3).
An attempt was made to identify breakdown products other
than cab acid, as cab acid was not being detected in all bait
samples. We did this using the solution that had been kept for
14 months at 4°C. Although the concentration of cabergoline had
fallen to 50% of its original concentration, there was only a minor
amount (2%) of cab acid detected by HPLC-MS. The only other
breakdown product detected was a minor component with ions
4 atomic mass units higher than cabergoline. This was possibly a
hydrogenated cabergoline, formed after long contact with the
reducing sugar, lactose, that was present in the Cabaser tablets.
Abstract
Cabergoline is a potent inhibitor of prolactin release and a potential fertility control agent for foxes. To understand how cabergoline could behave in baits deployed for fox control, we conducted laboratory and field trials to investigate the stability of cabergoline when ( 1) in solution, ( 2) injected into a bait ( deep- fried liver and Foxoff (R)) and ( 3) exposed to a range of environmental conditions, including burial. Cabergoline, dissolved in a 1% acetic acid solution, and its carboxylic acid hydrolysis product can be assayed using high- performance liquid chromatography. When stored at 4 degrees C and at room temperature, cabergoline in solution was stable for up to 36 days. When stored under cool (<= 15 degrees C), dry conditions, cabergoline ( 800 mu g) in commercial Foxoff (R) and deep- fried ox-liver baits was stable for 28 and 7 days, respectively; stability was reduced by increases in temperature ( tested up to 40 degrees C) and humidity. Recovery of cabergoline from buried baits exposed to a range of field conditions decreased rapidly in the first week, but after 56 days remained detectable at levels of 6 - 22% of the injected amounts. This study has important implications for baiting campaigns that use cabergoline for fox control.
(PDF Download Available). Available from:
Stability of cabergoline in fox baits in laboratory and field conditions (PDF Download Available)
Stability of cabergoline in solution
The stability of cabergoline in solution on storage was determined
with a solution of 1 mg mL–1 divided into ten 1-mL
aliquots placed into 1.5 mL Teflon septum-sealed, screw-capped
glass vials. The vials were kept at 4°C (n = 5) or 10–15°C
(ambient temperature) (n = 5) and analysed after 0, 7, 14 and
36 days. To investigate long-term stability in solution, we
assessed the concentration of cabergoline (1 mg mL–1 in 1%
acetic acid) after 14 months storage at 4°C. For analysis, 40 µL
were removed and diluted to 1 mL with 1% acetic acid, and
20 µL of this solution (nominally containing 800 ng cabergoline)
was injected into the HPLC.
To study the effect of pH on the stability of cabergoline,
80 µL of 1 mg mL–1 1% acetic acid were diluted to 2 mL with
distilled water or buffers of pH 7, 8 or 9. Phosphate buffer
(0.067 M) was used for pH 7 and 8, and carbonate buffer (0.1 M)
for pH 9. After incubation at 60°C (high temperature was used
to increase the rate of break down) for up to 120 min, 200-µL
aliquots were removed, acidified with 50 µL 0.25 M HCl, and
analysed by HPLC.
Results
Stability of cabergoline in solution
Calibration curves were prepared daily by dilution of the
primary solution of cabergoline with 1% acetic acid. The curves
showed excellent linearity over the range 10–1600 ng injected in
20 µL. However, curves were usually prepared over a smaller
range (10–800 ng) to suit the needs of the stability studies
(Fig. 1). The lower limit of quantification was taken to be the
lowest point (10 ng) on the curve. There was no loss of cabergoline
from solutions in 1% acetic acid when stored in the
refrigerator at 4°C or at room temperature for up to 36 days.
After 14 months’ storage at 4°C, however, the concentration of
cabergoline in solution had fallen by 50%.
When heated with base (pH 8 or 9), cabergoline disappeared
over time and was replaced by another peak that eluted just
before it (Fig. 2). HPLC-MS analysis confirmed that the caber
goline peak gave a characteristic [M + H+] ion at m/z 452, while
the earlier peak give an [M + H+] ion at m/z 297, and was the
carboxylic acid breakdown product (cab acid), formed by
hydrolysis of the acylurea bond in the cabergoline. The rate of
decomposition of cabergoline increased with increasing pH
(Fig. 3).
An attempt was made to identify breakdown products other
than cab acid, as cab acid was not being detected in all bait
samples. We did this using the solution that had been kept for
14 months at 4°C. Although the concentration of cabergoline had
fallen to 50% of its original concentration, there was only a minor
amount (2%) of cab acid detected by HPLC-MS. The only other
breakdown product detected was a minor component with ions
4 atomic mass units higher than cabergoline. This was possibly a
hydrogenated cabergoline, formed after long contact with the
reducing sugar, lactose, that was present in the Cabaser tablets.
