• Home
• About Leventa
  • Label
  • Handling
  • Stability
  • Storage
  • Syringes
• Using Leventa
  • Pharmacokinetics
  • Dosing
  • Dosage Adjustments
  • Converting to Leventa
• Hypothyroidism
  • About Hypothyroidism
    • Etiology
    • Signalment
    • Clinical Signs
    • Diagnosis
    • Euthyroid Sick Syndrome
  • Treatment
  • Monitoring & Control
• FAQs
• Contact Merck Animal Health

Treatment of Hypothyroidism

The therapy of choice for hypothyroidism is thyroid hormone supplementation with a synthetic levothyroxine product. With oral supplementation of T4, the serum concentrations of T4, T3 and TSH should return to normal in the hypothyroid dog. Ideally, a product with proven efficacy in dogs should be used, as some preparations of levothyroxine sodium have variable concentrations of active ingredient. (Fish et al, 1987). 

Leventa® is a once-a-day liquid formulation of levothyroxine sodium with a concentration of 1 mg per ml.   Pharmacokinetic studies have shown that Leventa’s liquid formulation allows for optimal absorption and bioavailability of levothyroxine sodium.  Once-a day treatment with Leventa® will maintain the serum T4 concentration within the therapeutic range for 24 hours.

Dosage of Leventa®
The dosage of Leventa® is 20 μg per kg s.i.d. (0.1 mL/10 lbs SID).  While the initial dosage of levothyroxine has traditionally been established to be 20 μg per kg b.i.d. (0.1 mL/10 lbs) , it has been confirmed through pharmacokinetic studies that Leventa® oral solution should be started at a dosage of 20 μg per kg s.i.d. (0.1 mL per 10 lbs s.i.d.). For example, a 50-lb. dog should receive 0.5 ml of Leventa® once daily.

Starting Dose of Leventa® When Treating Concurrent Disease
In the presence of concurrent disease (when euthyroid sick syndrome has been ruled out), the initial starting dose of Leventa® may need to be decreased, especially when increasing the metabolic rate of the hypothyroid patient may have undesirable effects. Cardiomyopathy is an example of a disease that may worsen when increasing the metabolic rate of the patient, since levothyroxine sodium may cause an increase in the heart rate and oxygen demand of peripheral tissues.¹

1. In such a case, start Leventa® at 25 percent of the recommended starting dose s.i.d. For Example, a patient who would normally receive 0.5 ml of Leventa® s.i.d. would instead receive 0.12 ml s.i.d. initially.  This dose may be gradually increased over the following four weeks, depending on the response by the patient.  For questions regarding specific hypothyroid cases, please contact our Technical Services department at 800-224-5318.

Converting a Patient to Leventa®
If a patient is currently on another levothyroxine sodium product at a dosage of 20 μg per kg b.i.d. (0.1 mL/10 lbs), and you would like to convert the patient to Leventa®, first measure the patient’s peak serum T4 and TSH concentrations.

If the patient is well regulated, (based on clinical signs and the T4 and TSH values), it is recommended to continue the patient on the original dose administered once daiy instead of twice daily. Therefore, a patient receiving 0.5 mg BID of another levothyroxine sodium product would initially receive 0.5 mL SID of Leventa®.

When converting a well-regulated patient from another levothyroxine sodium product at a dosage of 20 μg per kg s.i.d. (0.1 mL/10 lbs), start the patient on the same dosage of Leventa® (20 μg per kg or 0.1 mL/10 lbs s.i.d.).

Check the peak serum T4 and TSH concentration two to four weeks after changing from another product to Leventa® and adjust the dose as necessary based on the guidelines below.