|LETTER TO THE EDITOR
|Year : 2015 | Volume
| Issue : 3 | Page : 124-125
Phosphate binders bind levothyroxine and affect the control of hypothyroidism
Akihito Tanaka1, Yuichi Ito2
1 Department of Nephrology, Nakatsugawa City Hospital, Gifu Prefecture, Nakagawa-ku, Nagoya, Japan
2 Department of Emergency Medicine, Nagoya Ekisaikai Hospital, Nakagawa-ku, Nagoya, Japan
|Date of Web Publication||16-Oct-2015|
Dr. Akihito Tanaka
Department of Nephrology, Nakatsugawa City Hospital, 1522-1 Komaba, Nakatsugawa City, Gifu Prefecture - 508 8502
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Tanaka A, Ito Y. Phosphate binders bind levothyroxine and affect the control of hypothyroidism. Thyroid Res Pract 2015;12:124-5
The number of patients who receive regular hemodialysis (HD) is increasing. Among the HD patients, many patients show excessive high levels of phosphate and are administered phosphate binders, such as calcium carbonate (CaCO 3 ), sevelamer hydrochloride (SevHCl), lanthanum carbonate (LaCO 3 ) and so on. On the other hand, hypothyroidism is often seen. Complication of hypothyroidism in HD patients is not rare. Thyroid replacement therapy for HD patients must be performed carefully because phosphate binders bind not only phosphate but also to other medicines, including levothyroxine (LT4).
A female in her twenties had been administered LT4 for hypothyroidism from childhood. She initiated HD for end-stage renal disease (ESRD) due to reflux nephropathy 5 years ago. She started to receive regular HD sessions in our clinic last year. Then, she showed hyperphosphatemia, 8.7 mg/dl, with CaCO 3 4500 mg/day. And her hypothyroidism was well controlled with LT4 150 µg/day, such as thyroid stimulating hormone (TSH) 0.023 µU/ml, free triiodothyronine (FT3) 3.5 pg/ml and free thyroxine (FT4) 1.46 ng/ml. Additional administration of SevHCl 3000 mg/day for hyperphosphatemia was performed which resulted in the control of hypothyroidism getting worse (TSH 9.773 µU/ml). Simultaneously, she complained feeling colder than usual. We diagnosed exacerbation of hypothyroidism. We changed the timing of taking LT4 to at bedtime from morning because the timing was reported to be the best for absorption from intestine  and aimed to separate from phosphate binders. After change of timing, her hypothyroidism improved a little (TSH 5.185 µU/ml). We considered that addition of phosphate binders caused the exacerbation of hypothyroidism. Hence, we performed nutritional guidance. Then, hyperphosphatemia improved and withdrawal of SevHCl became possible, following improvement of hypothyroidism (TSH 2.642 µU/ml). However, she had large appetite and often could not control diet. The level of phosphats kept around 6 mg/dl or above. New administration of LaCO 3 (750 mg/day) made the control of hypothyroidism unstable (TSH 5.185 µU/ml). Hence, we performed nutritional guidance repeatedly. Successively, the control of hypothyroidism and hyperphosphatemia is improving (TSH 4.000 µU/ml and phosphorus 5.5 mg/dl with CaCO 3 4500 mg/day and SevHCl 3000 mg/day). Her clinical course is shown in [Figure 1].
|Figure 1: Clinical course of phosphate and TSH. The administration of phosphate binders were associated with increasing TSH levels. Sev HCl: sevelamer hydrochloride. CaCO3: calcium carbonate. LaCO3: Lanthanum carbonate. TSH: Thyroid stimulating hormone. LT4: Levothyroxine. P: Phosphate|
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This report confirms that phosphate binders, such as CaCO 3 , SevHCl and LaCO 3 , bind LT4 and make the control of hypothyroidism unstable. CaCO 3 is famous for this fact,  however, SevHCl  and LaCO3  also bind and affect absorption of LT4. For the HD patients with LT4 and phosphate binders, adjustment of phosphate binders must be careful. Increasing dose of phosphate binders may cause malabsorption of LT4 and make the control of hypothyroidism worse. Then, more dose of LT4 may be necessary. Or the timing of taking LT4 must be separated from phosphate binders at least 4 hours and is favorable at bedtime. Needless to say, the control of hyperphosphatemia is also important.
It is important to know that phosphate binders, not only CaCO 3 but also SevHCl and LaCO 3 bind LT4 and affect its absorption. Health care providers must know this fact and control hypothyroidism and hyperphosphatemia carefully.
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