Thyforon Dose

Hi, I’m hoping for some general advice on dosages of thyforon please. Our 31kg Golden Retriever was suffering from Hypothyroidism and was started on Thyforon a month ago. She was given 400 microgram (MCG) tablets and we were told to give 1.5 of these 400mcg tablets twice a day, which we did. Unfortunately now, after a blood test, we discover she is now Hyperthyroid (T4 over 70 - no surprise as she was showing clinical signs). When I look at the dose she’s been on, it looks like she’s been on double the starting dose? The starting dose appears to be 10ųg (10 micrograms?) per kg of body weight twice a day which would make 310 microgams of Thyforon twice a day for a 31kg dog - but she was on 600 mcg twice a day (1.5 x 400 mcg tablet twice a day). Am I missing something here? It looks like she’s been on double the starting dose so not really a surprise her T4 is through the roof? We were told  they were starting her on a very low dose and didn’t question the initial dosage. We have now been told to give her 1.5 tablets (600mcg) once a day instead of twice. This still seem high to me? I’m sure I’m missing something or maybe there’s just been a pharmacy error but I’d be really grateful of any advice please. Many thanks.

The recommended starting dosage of levothyroxine sodium, according to the datasheet, appears to be 10 µg/kg (ten micrograms per kilo of body weight) orally every 12 hour.  Please note that I know nothing about this particular patient and these particular circumstances, but I would tend to agree with you that what you describe looks to be unusual and would recommend asking the vet, and / or the practise leader, about this.

If you look inside the drug-packet, you should have been provided with what is known as a data-sheet.  Usually this is a page of very small-print, giving supplementary guidance as to how the drug should be dosed - this may be what you have already read.  I quote:  Overdoses of three up to six times label recommended starting dose for 4 consecutive weeks in healthy, euthyroid dogs resulted in no significant clinical signs.  However, where high doses were given long-term, side effects were reported such as excessive drinking, excessive urinating, weight-loss, a rapid heart-rate and 'nervousness'.  The presence of these signs should result in evaluation of T4 serum concentrations to confirm (that the dose is too high) and immediate discontinuance of the supplementation.  The sheet goes on to reccommend that once these signs have stopped and the animal has recovered, days to weeks later, the dose should be reviewed and the drug restarted under close observation.  Again, your vet will have a copy of the data-sheet and should be prepared to talk about any concerns.