Can you start levothyroxine with TSH 7.75 on lithium 300mg?

Management of Hypothyroidism in a Patient on Lithium with TSH 7.75

Levothyroxine therapy should be initiated for a patient with TSH 7.75 who is on lithium 300mg, as this represents subclinical hypothyroidism that warrants treatment, especially given the known thyroid-suppressive effects of lithium therapy. 1

Rationale for Treatment

Lithium therapy is known to affect thyroid function in several ways:

• Inhibits thyroid hormone release from the thyroid gland 2
• May inhibit peripheral conversion of T4 to T3 in some patients 3
• Increases risk of hypothyroidism in approximately 20% of patients 2
• Can cause goiter in up to 40% of patients 2

The TSH level of 7.75 mIU/L represents subclinical hypothyroidism that warrants treatment, particularly in the context of lithium therapy which likely contributed to this thyroid dysfunction.

Treatment Protocol

1. Initial Dosing:

   • Start levothyroxine at a dose of approximately 1.6 mcg/kg/day for average-weight adults without risk factors 1
   • For patients over 60 years or with cardiac disease, start with a lower dose (25-50 mcg/day) 1
   • Administer as a single daily dose on an empty stomach, 30-60 minutes before breakfast with a full glass of water 4

2. Medication Administration:

   • Take levothyroxine at least 4 hours before or after drugs that may interfere with absorption 4
   • Do not administer with foods that decrease absorption (e.g., soybean-based products) 4

3. Monitoring:

   • Check TSH and free T4 levels 6-8 weeks after initiating therapy 1
   • Target TSH level within normal reference range (0.4-4.0 mIU/L) 1
   • Once adequately treated, repeat testing every 6-12 months or as indicated for a change in symptoms 5

Special Considerations with Lithium

• Continue lithium therapy: Lithium treatment should not be stopped if a patient develops thyroid abnormalities, as it may be essential for managing bipolar disorder 6
• More frequent monitoring: Consider checking thyroid function more frequently (every 4-6 months) due to ongoing lithium therapy 6
• Watch for progression: Lithium may cause progressive thyroid dysfunction over time, so continued vigilance is necessary 7

Potential Pitfalls and Caveats

1. Avoid overtreatment: Starting with too high a dose in elderly or cardiac patients can cause cardiac complications
2. Medication interactions: Ensure proper spacing between levothyroxine and other medications that may affect absorption
3. Monitoring compliance: Emphasize the importance of consistent daily dosing and regular follow-up
4. Continued lithium effect: Be aware that thyroid function may continue to be affected by ongoing lithium therapy, requiring dose adjustments over time
5. TSH variability: Remember that a single abnormal TSH value should not be the sole basis for diagnosis or treatment decisions 5

When to Consult Endocrinology

Consider endocrine consultation in the following scenarios:

• Unusual clinical presentations
• Concern for central hypothyroidism
• Difficulty titrating hormone therapy 5
• Development of goiter or thyroid nodules 6

Proper management of hypothyroidism in patients on lithium therapy requires balancing the need for adequate thyroid hormone replacement while continuing necessary psychiatric treatment.