The Effect of Calcium Supplements on Levothyroxine after Total Thyroidectomy: Results from a Single Centre, Retrospective Study in Kelantan, Malaysia

Thyroid hormone replacement (levothyroxine) needs to be prescribed and calcium supplements may be administered with levothyroxine to overcome hypocalcaemia following total thyroidectomy. Evidences have shown that there is an interaction between those two. Therefore, we aimed to assess the effect of calcium supplements on levothyroxine after total thyroidectomy. Methods: A retrospective study was conducted from 1 April to 30 September 2022 involving all patients who underwent total thyroidectomy in Hospital Raja Perempuan Zainab II, Kelantan, Malaysia from 1 January 2019 to 31 December 2020. They were prescribed either levothyroxine or levothyroxine with calcium supplements for at least three months after the surgery. Those with incomplete data were excluded. Thyroxine (T4), thyroid stimulating hormone (TSH) and calcium levels were compared between patients receiving levothyroxine with and without calcium supplements using independent t-test in Statistical Package for Social Sciences (SPSS) version 22.0. A statistically significant test result was set at a P-value of less than 0.05. Results: A total of 50 patients were included in the study. They were mostly prescribed levothyroxine with calcium supplements (74%, n=37). When compared, those taking both medications had significantly lower T4 [11.56 (4.04) pmol/L vs 15.68 (7.59) pmol/L; P=0.017] and higher TSH [9.66 (12.44) vs 1.13 (1.54); P<0.001] levels. However, there was no significant difference of calcium levels between patients receiving levothyroxine with and without calcium supplements [2.13 (0.22) vs 2.13 (0.16), P=0.929). Conclusion: Calcium supplements were observed to have an effect on levothyroxine after total thyroidectomy. Thus, it is important for healthcare providers and patients to be aware of the interaction between levothyroxine and calcium supplements