Block & replace regime versus titration regime of antithyroid drugs for the treatment of Graves' disease: a retrospective observational study.

Context: Two widely used antithyroid drug (ATD) regimes for Graves' disease (GD) include the 'block & replace' (B&R) regime (a fixed high-dose of ATD combined with levothyroxine) and the 'titration' regime (a titrating dose of ATD). Anecdotally, it is believed that B&R is less prone to fluctuating thyroid function.

Objective: To study whether, in routine clinical practice, the B&R regime, compared with the titration regime, is associated with more stable thyroid function.

Methods: We retrospectively analysed case-records for 450 patients treated with ATDs for GD at a secondary care hospital. Exclusion criteria included treatment with ATDs for <6 months, thyrotoxicosis due to other causes, treatment with radioiodine or thyroidectomy and pregnancy.

Results: Two hundred and twenty three patients were treated with the B&R regime ('B&R group'), 149 with the titration regime ('titration group') and 78 with both regimes. The number of thyroid function tests (TFTs) performed per year (mean(SD): 3·2(1·2) vs 3·4(1·5); adjusted mean difference = -0·4; 95% CI: -0·7 to -0·1; and P = 0·008) and the number of hospital clinic visits per year (mean (SD): 2·9 (1·0) vs 3·2 (1·3); adjusted mean difference = -0·4; 95% CI: -0·7 to -0·2; and P = 0·002) were lower in the B&R group than the titration group. The number of abnormal TFT results per year was similar in the two groups (mean(SD): 1·8(1·3) vs 1·8(1·4); adjusted mean difference = 0·05; 95%CI: -0·3 to 0·4; and P = 0·74).

Conclusions: In this retrospective study, there was little evidence that patients under B&R have more stable thyroid function. Further data from prospective studies, however, are needed to confirm this finding.