Pharmacokinetics/pharmacodynamics are helpful in drug development and regimen adjustment for refractive or extralabel applications. However, we must realize that this field is of secondary importance to a properly conducted clinical trial, says Mike Apley, DVM, PhD, Dipl. ACVCP, Kansas State University.
“Areas where we can mislead ourselves include forgetting about railers in our evaluation of treatment outcome, applying high-risk clinical trial outcomes to low-risk cattle, looking at days-on-feed (DOF) when mortalities occur rather than the DOF for fatal disease onset (their first treatment for that disease), and finally considering a drug that reduces fever to be doing the same thing as an antimicrobial that reduces fever because it helps the body overcome the source of the fever,” Apley says.
There are things we still don't know after all these years of research such as does routine revaccination or vaccination in the face of an outbreak do us any good? What is the optimal duration of therapy for BRD? “We can't confuse how long we wait to determine success/failure with how long they are actually receiving therapy,” Apley states. Does switching the drug for the next therapy really do any good? What are the best criteria to classify cattle as being in need of treatment for control of BRD?
"My biggest frustration," Apley says, "is what is going on with those groups of cattle that just keep giving us pulls throughout the feeding period? I am convinced all the things we try on them just depend on the timing of our rain dance. If allowed a chance to guess I would vote that we have some genetic lines with absolute crap immune systems. How many veterinarians work with a yard that has elected to stop feeding cattle from a certain ranch?”