Primary Hypothyroidism: When Initial Levothyroxine Has Not Normalised TSH
Not all patients reach the TSH target on an initial levothyroxine regimen. When a standard first-line course is completed but the thyroid-stimulating hormone level remains outside the normal range at reassessment, a structured next step is required.
Prior therapy: Levothyroxine — standard weight-based initial dosing, taken once daily under the prescribed timing conditions.
Target not achieved: TSH within the normal range (0.4 to 4.5 mIU/L) on recheck at six to eight weeks.
When TSH remains out of range after initial therapy, the protocol involves a directed approach to levothyroxine dosage adjustment — guided by the direction of the TSH deviation — with reassessment at defined intervals until the target is met. The complete adjustment algorithm is available in the full protocol.
References
- If the TSH level is abnormal, the clinician should assess patient adherence, evaluate drug-drug interactions, and adjust the levothyroxine dosage every six to eight weeks until the TSH level normalizes (Figure 2).
- When TSH is high (under-replacement), the daily dosage is increased by 12.5 to 25 mcg per day.
- When TSH is low (over-replacement), the daily dosage should be decreased by 12.5 to 25 mcg.