Action and use
Antihelminthic; ectoparasiticide
DEFINITION
Moxidectin Pour-on is a pour-on solution. It contains Moxidectin in a suitable vehicle.
The pour-on complies with the requirements stated under Veterinary Liquid Preparations for Cutaneous Application and with the following requirements.
Content of moxidectin, C37H53NO8
90.0 to 110.0% of the stated amount.
IDENTIFICATION
A. Carry out the method for thin-layer chromatography, Appendix III A, using the following solutions.
(1) Dilute a quantity of the pour-on solution, with shaking, in sufficient methanol to produce a solution containing 0.04% w/v of Moxidectin; filter a 5-mL portion through a 0.45-μm PTFE membrane filter and use the filtrate.
(2) 0.04% w/v of moxidectin BPCRS in methanol.
CHROMATOGRAPHIC CONDITIONS
(a) Use as the coating silica gel.
(b) Use the mobile phase as described below.
(c) Apply 5 μL of each solution.
(d) Develop the plate to 15 cm.
(e) After removal of the plate, dry in air, spray with anisaldehyde solution R1, heat at 105° for 5 to 10 minutes and allow to cool.
MOBILE PHASE
8 volumes of a 15% w/v solution of ammonium acetate adjusted to pH 9.6 with ammonia, 19 volumes of propan-2-ol and 43 volumes of ethyl acetate.
CONFIRMATION
The principal spot in the chromatogram obtained with solution (1) corresponds in position, colour and size to that in the chromatogram obtained with solution (2).
B. In the Assay, the retention time of the principal peak in the chromatogram obtained with solution (1) is similar to that of the principal peak in the chromatogram obtained with solution (2).
ASSAY
Carry out the method for liquid chromatography, Appendix III D, using the following solutions in acetonitrile.
(1) Dilute a weighed quantity of the pour-on solution to produce a solution containing 0.1% w/v of Moxidectin, shake and mix with the aid of ultrasound for 10 minutes. Allow to cool and filter the resulting solution through a 0.45-μm membrane
filter, discarding the first few mL of filtrate.
(2) 0.1% w/v of moxidectin BPCRS.
(3) 0.1% w/v of moxidectin for system suitability EPCRS.
CHROMATOGRAPHIC CONDITIONS
(a) Use a stainless steel column (15 cm × 3.9 mm) packed with end-capped octadecylsilyl silica gel for chromatography (4 μm) (Waters Nova-Pak and Waters Pico-Tag are suitable).
(b) Use isocratic elution and the mobile phase described below.
(c) Use a flow rate of 2.5 mL per minute.
(d) Use a column temperature of 50°.
(e) Use a detection wavelength of 242 nm.
(f) Inject 10 μL of each solution.
MOBILE PHASE
40 volumes of a 1.925% w/v solution of ammonium acetate in water, adjusted to pH 4.8 with glacial acetic acid, and 60 volumes of acetonitrile.
When the chromatograms are recorded under the prescribed conditions the retention time of moxidectin is about 12 minutes and the retention time of impurity D relative to that of moxidectin is about 0.94.
SYSTEM SUITABILITY
The test is not valid unless, in the chromatogram obtained with solution (3), the peak-to-valley ratio is at least 3.0 where Hp is the height above the baseline of the peak due to impurity D and Hv is the height above the baseline of the lowest point of the curve separating this peak from the peak due to moxidectin.
DETERMINATION OF CONTENT
Determine the weight per ml of the pour-on solution, Appendix V G, and calculate the content of C37H53NO8, weight in volume, using the declared content of C37H53NO8 in moxidectin BPCRS.
