In vitro susceptibility testing using the broth dilution method does not accurately reflect the true antimicrobial activity for CTC vs. slow growing organisms like Mycoplasma hyopneumoniae because of the tendency for chlortetracycline hydrochloride todegrade in the media over the prolonged incubation times required by these organisms. The relative results from studies using broth dilution to compare MIC values for TC, CTC and OTC for slow growing organisms like mycoplasma spp, could be questionable.The in vitro antimicrobial susceptibility profile is only one part of the antibiotic decision-making process. The pharmacokinetic/pharmacodynamic characteristics should also be taken into consideration. Feedgrade CTC is formulated to be stable in feed until consumed by the pig, A recently completed study confirmed that 97% of the CTC activity was still present in the feed at 28 days post-manufacture. This is in contrast to water soluble CTC which must be mixed fresh daily to maintain potency.
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