Research Communications of the 24th ECVIM-CA Congress

Ten of the 19 cats were started on a once-daily L-T4 regimen (100 lg); of these, only 2 (20%) had suppression of high serum TSH values into the reference interval (RI). Of the 8 cats that had persistently high TSH values, 5 were switched to twice-daily administration (75-100 lg, BID), which successfully lowered high TSH concentrations in 4 cats. The remaining 9 cats were started on twice daily L-T4 (75 lg, BID); of these, normalization of TSH occurred in 5 cats. Overall, L-T4 treatment was successful in normalizing TSH concentrations in 11 (58%) cats, 2 with once-daily and 9 with twice-daily dosing. Peak serum T4 concentrations of ≥30 nmol/L were needed in most cats to normalize TSH values. Higher serum T4 and lower TSH concentrations were achieved when L-T4 was administered on an empty stomach rather than given with food. A significant decrease (P < 0.003) in serum creatinine occurred after treatment with L-T4.