The pharmacokinetics of serum total thyroxine concentration (TT4) in euthyroid dogs was studied after concomitant administration of a levothyroxine oral solution with different types of dry diet.
Mixing levothyroxine with different types of dry diet did not have any effect on TT4 pharmacokinetics in the dogs. This finding indicates that changing from one diet to another during levothyroxine-replacement therapy should not impact therapeutic effectiveness, and should be helpful for improvement of compliance with thyroid hormone replacement therapy in dogs treated for life with this replacement therapy.
Source : R. Iemura et al., 2013. Effects of type of diet on pharmacokinetics of levothyroxine sodium oral solution. Res Vet Sci online January 2013. doi: 10.1016/j.rvsc.2012.12.010