During April 2017 our laboratory has been working on developing an assay for the veterinary antibiotic ceftiofur
Why do we need an assay for ceftiofur?
In Australia there are two formulations of ceftiofur:
- ceftiofur sodium which is registered for use in horses, cattle, and dogs and
- ceftiofur crystalline free acid (CFA) (marketed as Excede® by the company Zoetis, West Ryde, NSW) which is registered to treat lung infections in cattle. This formulation is interesting as a single dose is effective in cattle for up to 5 days.
So we have had a request from Dr Larry Vogelnest, senior veterinarian at Taronga Zoo whether CFA may be useful for the treatment of ‘Lumpy Jaw’ in kangaroos and wallabies. These animals eat tough grasses and these grasses along with teeth grinding cut the gums and make a pathway for bacteria in the mouth to enter the jaw resulting in bone infections. So Larry suggested that we determine the best dosage of CFA to treat bone infections in these Australian marsupials.
So in order to work out the best dosage…. we need to administer the CFA to the animals and detect the concentration in the blood. So we need an assay to measure the CFA in the blood.
Why is the assay tricky?
The CFA assay is one of the trickiest assays we have done!
When ceftiofur is administered to animals it rapidly undergoes metabolism and is converted to desfuroylceftiofur (DFC) which also has antibacterial activity. So we need to detect the concentrations of ceftiofur and DFC. So the strategy to do this is to convert all the ceftiofur to DFC.
How is this done? Firstly the ceftiofur needs to be cut into two molecules. One of these molecules is the desfuroylceftiofur. This molecule then undergoes stabilisation to desfuroylceftiofur acetamide…. which is what we can measure on the machine readout. We can then relate the concentration of desfuroylceftiofur acetamide back to the original CFA concentration. We have worked out this assay in sheep plasma and look forward to planning a CFA study in some kangaroos and wallabies.