Associate Prof Bill Pomroy from Massey University said how farmers used the new Zolvix drench, developed by Novartis Animal Health, would be interesting, but they had to use it to ensure they got maximum mileage.
Queenstown recently hosted the international launch of the first new drench family to be released in over 25 years, at which Prof Pomroy said drench resistance was slowly increasing and farmers could strategically use Zolvix to extend the life of cheaper drenches.
Novartis said because Zolvix acted differently from existing drenches by attacking the nervous system of internal parasites, it killed parasites that were resistant to existing drenches.
The actual cost of drench resistance was not known but estimated at between $200 million and $300 million in lost production.
Novartis has not yet announced the cost of Zolvix but said it would be the most costly drench on the market.
It took eight years to develop at a cost of between $200 million and $600 million.
The company's head of animal health parasitology research, Dr Ronald Kaminsky, said his work was inspired by an email in 2000 to New Zealand staff asking if drench resistance was a problem.
When told it was, he started work and discovered a new chemical family, called AAD, from which his team synthesised more than 700 molecules, of which Zolvix was the first to show real promise.
Dr Kaminsky said it consistently killed 99.9% of intestinal parasites, including those resistant to other drench families because it operated by interfering with the nervous system of the parasite.
The registration document extends to more than 100,000 pages and Dr Kaminsky said Zolvix had been proven safe for animals, humans and the environment.
While it would be expensive (its retail prices has not been set yet), Dr Kaminsky said rates of application were lower than existing drenches.
Novartis global brand manager for farm animal marketing Arthur Redpath said farmer research revealed that drench application was the second most significant issue they faced.
He said this highlighted how animal health companies had not given farmers a choice.
Drench was sold in 20-litre drums, which were difficult to dispose of, and guns were of a generic pistol-type design.
Novartis decided to redesign the applicator and sold Zolvix in one, two-and-a-half and five-litre aluminium pouches, which could be recycled or disposed of and which fitted into a backpack designed so the weight was carried around the hips and not the shoulders or back.