From the Guidelines
Cynomel (liothyronine) dosing for thyroid hormone replacement should start at 5-12.5 mcg daily for adults, with gradual increases based on clinical response and thyroid function tests, considering the patient's age, frailty, and comorbidities, such as cardiac disease. For patients without risk factors, full replacement can be estimated using ideal body weight for a dose of approximately 1.6 mcg/kg/d, as suggested by recent guidelines 1. However, for those older than age 70 years and/or frail patients with multiple comorbidities, including cardiac disease, it is recommended to titrate up from a lower starting dose of 25-50 mcg, to minimize the risk of adverse effects. Key considerations in dosing and monitoring include:
- Starting dose: 5-12.5 mcg daily for adults
- Dose adjustments: Gradual increases of 5-12.5 mcg every 1-2 weeks until the desired therapeutic effect is achieved
- Maintenance dose: Usually ranges from 25-75 mcg daily, divided into 2-3 doses
- Monitoring: Thyroid function tests (TSH, free T3) every 2-4 weeks during dose adjustments and then every 6-12 months once stable, along with regular assessment of clinical symptoms
- Special considerations: Elevated TSH can be seen in the recovery phase of thyroiditis, and in asymptomatic patients with FT4 that remains in the reference range, it is an option to monitor before treating to determine whether there is recovery to normal within 3-4 weeks, as indicated by 1. Development of a low TSH on therapy suggests overtreatment or recovery of thyroid function, and dose should be reduced or discontinued with close follow-up, as per 1.
From the Research
Cynomel (Liothyronine) Dosing and Monitoring
- Cynomel, also known as liothyronine, is a synthetic form of the thyroid hormone triiodothyronine (T3) used in patients requiring thyroid hormone replacement 2.
- The appropriate dosing of liothyronine in combination with levothyroxine (LT4) for patients who remain symptomatic on LT4 therapy is to reduce the LT4 dose by 25 mcg/day and add 2.5-7.5 mcg liothyronine once or twice a day 2.
- For patients with primary hypothyroidism, a normal thyrotropin (TSH) level of 1-2 mU/L is considered the determinant of optimal daily levothyroxine sodium dose, whereas normal thyroxine and triiodothyronine levels in the mid or upper normal range may denote optimal replacement in patients with central hypothyroidism 3.
- Monitoring of thyroid function is vital in patients on liothyronine therapy, with regular checks of TSH, free T4, and free T3 levels to avoid over-replacement or under-replacement 4, 5.
Special Considerations
- In elderly patients or those with a history of coronary artery disease, it is recommended to start with a low dose of levothyroxine and gradually titrate to the full calculated dose to avoid cardiac events 3.
- Chronic over-replacement with thyroid hormone may induce osteoporosis, particularly in postmenopausal women, and should be avoided 3.
- Patients on liothyronine therapy should be monitored for adverse effects, such as transient episodes of hypertriiodothyroninemia, and the dose adjusted accordingly 2.
Clinical Practice
- Combination therapy with LT4 and LT3 may be considered for patients who remain symptomatic despite adequate levothyroxine monotherapy, but this should be undertaken by clinicians experienced in the field with appropriate monitoring for adverse outcomes 5.
- The use of desiccated thyroid extract, which contains a combination of T4 and T3, is not formally regulated by the FDA, and consistency of T4 and T3 contents is monitored by manufacturers only 2.