From the Guidelines
Patients on Xtandi (enzalutamide) may need their levothyroxine dose adjusted due to the potential interaction between enzalutamide and levothyroxine metabolism. According to the study 1, enzalutamide is a novel AR signaling inhibitor that can affect thyroid function, with 8.1% of patients experiencing hypothyroidism compared to 2.0% in the placebo group.
Key Considerations
- Enzalutamide is a strong CYP3A4 enzyme inducer that can increase the metabolism of levothyroxine, potentially reducing its effectiveness.
- Patients taking both medications should have their thyroid function tests (TSH and free T4) monitored more frequently, especially in the first 2-3 months after starting Xtandi or after any dose changes.
- If TSH levels rise above the target range, the levothyroxine dose may need to be increased by approximately 25-50% to maintain euthyroid status.
Monitoring and Dose Adjustment
- Patients should be educated about potential symptoms of hypothyroidism (fatigue, cold intolerance, weight gain, constipation) and advised to report these promptly to their healthcare provider for appropriate dose adjustments.
- The exact adjustment depends on individual patient factors and laboratory results, and close monitoring is necessary to ensure optimal thyroid hormone levels.
Clinical Implications
- The interaction between enzalutamide and levothyroxine highlights the importance of regular monitoring and potential dose adjustments to prevent hypothyroidism and ensure optimal patient outcomes.
- Healthcare providers should be aware of this potential interaction and take steps to mitigate its effects, including frequent monitoring and patient education.
From the Research
Levothyroxine Dose Adjustment and Xtandi
- There is no direct evidence in the provided studies to suggest that Xtandi affects levothyroxine dose adjustment.
- However, studies suggest that various factors can influence levothyroxine dose adjustment, including concomitant medical conditions and medications 2.
- Levothyroxine therapy requires careful management and dose adjustments to maintain biochemical and clinical euthyroidism throughout a patient's lifetime 2.
- Physicians should consider a patient's overall medical situation, including any concomitant medications, when adjusting levothyroxine doses 3, 2.
- The clinical utility of thyroid function tests, including TSH and free thyroid hormone tests, is crucial in managing thyroid disorders, but results should be interpreted in the context of the patient's clinical situation 4, 5, 3.
Factors Influencing Levothyroxine Dose Adjustment
- Physiological changes throughout life, such as weight or hormonal changes, may require levothyroxine dose adjustments 2.
- Concomitant medical conditions, certain medications, and pregnancy may also necessitate dose adjustments 2.
- Patients should be closely monitored, and their levothyroxine therapy should be adjusted accordingly to maintain euthyroidism and prevent adverse events 2.