Public health assessment
In 2003 the APVMA commissioned a review of publicly available scientific literature relating to antimicrobial resistance and macrolides. This assessment found that although there was qualitative evidence that antimicrobial use in animals can lead to resistance in bacteria or to their resistance genes being passed to humans via the food chain, there were no reports recording the specific transfer of macrolide resistance, from animals to humans, in Campylobacter spp. and Enterococci spp., two food-borne bacterial genera of concern in the context of macrolide antibiotics.
The APVMA also reviewed a quantitative risk assessment of tylosin prepared by a registrant in 2005. The risk assessment was not comprehensive enough to determine that the likelihood of developing resistance to macrolide was very low, as concluded in the risk assessment report.
In 2013 the APVMA commissioned an assessment of sub-therapeutic administration of tylosin to food-producing animals and its impact on antimicrobial resistance. This concluded that the sub-therapeutic use of tylosin will encourage the emergence and maintenance of resistant strains not only to tylosin but also to the more important related veterinary macrolides.
Efficacy
APVMA commissioned an assessment of the efficacy studies submitted to the review. This assessment concluded that kitasamycin is efficacious in improving average daily weight gain in pigs between 4.7 kg and 35 kg. Tylosin has been shown to be effective in improving average weight gain in pigs under a range of conditions, although its effect on food conversion efficiency appears to be more variable. Tylosin, at labelled doses, has a significant effect on susceptible disease agents including Brachyspira hyodysentriae, Lawsonia intracellularis, Mycoplasma hyopneumoniae, Erysipelothrix rhusiopathiae and Actinobacillus pleuropneumoniae, which may explain the positive effect of tylosin on weight gain and food conversion efficiency. Tylosin has also been shown to control liver abscessation in feedlot cattle. No data supporting the claims of efficacy of oleandomycin were provided for this review.
Scheduling committee decision
At the commencement of the review in 2001, products containing 50 ppm or less of tylosin were classified in Schedule 5 of the Standard for the Uniform Scheduling of Medicines and Poisons (SUSMP) and could be sold in retail outlets without a veterinary prescription. From 1 June 2014, all registered macrolide products were classified in Schedule 4 of the SUSMP, meaning that such products can only be supplied through veterinary prescription.
