New flukicide too similar to closantel, warn vets

A move to give full UK licensing to the previously specially imported flukicide rafoxanide should be met with caution by farmers due to its chemical similarities to closantel.

This is according to industry bodies Control of Worms Sustainably (Cows) and Sustainable Control of Parasites in Sheep (Scops) in light of “confusion” around the active.

Rafoxanide is not an appropriate alternative to closantel due to it being similar in mode of action and chemical make-up, according to a joint Cows and Scops announcement.

See also: The risks of using rafoxanide for liver fluke explained

“With a very limited number of different flukicide actives in the armoury and increasing reports of resistance to triclabendazole (TCBZ), product choice is extremely important,” said the statement.

Rafaxonide is an adulticide, shown to achieve an 80-99% kill rate when fluke are 10-12 weeks old (adult stage) and is for use in spring and summer, vets advise.

An industry source said Flukanide by Univet is the sole rafoxanide product licensed and available in the UK. It was initially imported on a special certificate in 2019 from Ireland, but is now fully licensed.

The following four messages have been underlined by Cows and Scops.  

1. Rafoxanide is not a new flukicide

Some countries (Ireland and Australia) have been using the active since the 1980s. 

2. Rafoxanide is the same class as closantel and oxyclozanide

There is evidence of cross-resistance between rafoxanide and closantel in field and laboratory studies.

3. Do not rotate with closantel

Using rafoxanide interchangeably with closantel will hasten the development of resistance to closantel.

4. Spring and summer use

Rafoxanide is only effective against adult fluke, so it is an option in the spring or early summer, providing closantel has not been used earlier in the season.

Table of flukicides (sheep)

Active ingredient Age of fluke (kill rate %) Optimum time of year to use
  1 2 3 4 5 6 7 8 9 10 11 12+
Albendazole                   50-70 80-99 Spring/summer
Oxyclonazide                   50-70 80-99 Spring/summer
Nitroxynil                    50-90        91-99 Late autumn/winter
Closantel           23-73 91               91-85      97-100 Autumn
Triclabendazole 90-99                                   99-99.9 Autumn
Source: Professor Diana Williams