Leventa^® Questions and Answers

Feeding does have a significant effect on the absorption of Leventa. Dogs given Leventa on an empty stomach (at least 2 hours prior to feeding) will absorb around 50% more than those dogs given Leventa with food¹. It is therefore essential that the timing of feeding and Leventa dosing is consistent.

In order to achieve consistent absorption of L-thyroxine, it is recommended to administer L-thyroxine 2 – 3 hours prior to feeding, which will maximise the degree of absorption and minimize variation in absorption.

If Leventa is administered less than 2 hours before feeding, at or after feeding, the feed given (type and amount) should be standardised.

Dogs that have concurrent cardiac disease, diabetes mellitus or Addison’s need to be started on treatment cautiously.  It is recommended to start these dogs on 25% of the normal dose (5μg/kg) and increase by 25% increments every 2 weeks until stabilised. 

Cardiac disease – by supplementing these dogs with thyroid hormone the metabolic rate will increase and there may also be an increase in activity levels.  This may increase myocardial and peripheral tissue oxygen consumption and increase heart rate and may increase blood pressure which could worsen cardiac disease. 

Diabetes – Insulin requirements may change once treatment for hypothyroidism commences.  In most cases there will be a reduction in the amount of insulin required, however the reverse can also happen (due to increased insulin catabolism).  Blood glucose should be monitored carefully 

Addison’s – Dogs must have their Addison’s controlled prior to starting thyroid replacement.  T4 supplementation must be started gradually to prevent a hypoadrenocortical crisis. 

L-thyroxine absorption may be impaired by the concomitant administration of antacids, e.g. aluminium or magnesium salts or calcium carbonate, or ferrous sulphate, and sucralfate. Therefore, concomitant administration of Leventa with the above mentioned compounds should be avoided. At least 2 hours should elapse between administration of Leventa and such products.

The therapeutic response to Leventa may be altered by any compound that influences thyroid hormone metabolism and disposition (e.g. drugs displacing protein-binding site, modifying serum thyroxine-binding globulin concentration, or altering hepatic degradation of thyroxine or peripheral conversion of thyroxine to triiodothyronine). Thus, in case of concomitant administration of Leventa with a compound exhibiting one of these properties, it is recommended to recheck that thyroid hormone concentrations are appropriate and to adjust the dose of Leventa accordingly if needed.

Conversely, L-thyroxine supplementation may affect the pharmacokinetics and activity of concurrent therapies. In diabetic dogs treated with insulin, L-thyroxine supplementation may alter insulin requirements. In dogs with cardiac insufficiency, therapeutic response to cardiac glycosides may be decreased by L-thyroxine supplementation. Therefore, if treated with any of these compounds, dogs should be monitored carefully during initiation of treatment with Leventa.