Use of a 1-n-(halo-3-pyridylmethyl)-n-methylamino-1-alkylamino-2-nitroethylene derivative for preparing a topical veterinary pharmaceutical composition for combating external parasites

A method of topically administering to a domestic animal a composition comprising at least one 1-N-(halo-3-pyridylmethyl)-N-methylamino-1-alkylamino-2-nitroethylene derivative of formula (I) below:

• in which:
• Hal represents a halogen atom chosen from fluorine, chlorine, bromine and iodine,
• R1 and R2, which may be identical or different, represent a hydrogen atom, a C1-C6 alkyl radical or a C3-C7 cycloalkyl radical,
• R3 represents a hydrogen atom or a C1-C6 alkyl radical,
• and of at least one pharmaceutically acceptable carrier,
• wherein said animal is a cat, and
• wherein said composition is applied to said animal at four week or more intervals to kill external parasites on said animal.