REASSESSING CARBIMAZOLE DOSING STRATEGIES

ASSOCIATION BETWEEN INITIAL DOSE AND SIX-WEEK THYROID FUNCTION

Abstract

INTRODUCTION
Carbimazole is a commonly used antithyroid medication for the treatment of hyperthyroidism. Dosage recommendations typically vary based on the severity of biochemical hyperthyroidism, particularly free thyroxine (FT4) levels. However, real-world dosing practices may deviate from guideline-based recommendations, potentially leading to suboptimal outcomes such as persistent hyperthyroidism or iatrogenic hypothyroidism. This study evaluates whether adherence to recommended dosing based on initial FT4 levels is associated with appropriate thyroid function outcomes at six weeks.

METHODOLOGY
We conducted a retrospective observational study involving 125 patients with confirmed hyperthyroidism. Patients were categorized based on whether their initial carbimazole dose was lower than, consistent with, or higher than the recommendations outlined in the American Thyroid Association guidelines. Thyroid function outcomes at 6 weeks were classified as euthyroid, hypothyroid, or persistent hyperthyroid based on repeat thyroid function tests. A chi-square test was performed to evaluate the association between dosing appropriateness and thyroid outcome.

RESULT
The mean age of participants was 48.9 years (SD = 15.0). Based on initial FT4 values, 23.2% were within 1–1.5× upper normal limit (UNL), 23.2% were 1.5–2× UNL, and 53.6% were >2× UNL. Among the 63 patients who received a correct dose, 58.6% became hypothyroid, and 35.0% became euthyroid. In contrast, 52.5% of those given a lower dose achieved euthyroidism, while only 17.2% became hypothyroid. Higher-than-recommended doses resulted in 24.1% hypothyroid outcomes. The chi-square test demonstrated a statistically significant association between dose category and thyroid outcome (p = 0.003).

CONCLUSION
Initial carbimazole dosing based on FT4 levels is significantly associated with short-term thyroid outcomes. Interestingly, lower-than-recommended doses were more likely to achieve euthyroidism without excessive hypothyroidism. These findings suggest the need to re-evaluate dosing strategies to optimize early treatment outcomes and reduce the risk of overtreatment in hyperthyroid patients.