Clinical exacerbations of hyperthyroidism caused by RAI treatment are relatively uncommon. Pretreatment with antithyroid drugs have been shown to attenuate transient increases in thyroid hormone levels following treatment (35). They may also lower the baseline hormone levels, reducing the clinical significance of any transient increase in these levels (36). Beta blockers may reduce symptoms related to hyperthyroidism, although it should not be solely relied upon to prevent impending thyroid storm. To reduce symptoms which may occur during treatment, beta-blocker medications, such as propranolol, 80-160 mg/day, or atenolol, 50-150 mg/day, can be considered in patients without significant contraindications to this class of medication. Beta blockers may be continued during RAI treatment.
To reduce morbidity from hyperthyroidism and prevent worsening of symptoms before the effects of radioiodine are realized, patients may also be given antithyroid medications several days before or after RAI treatment. If given, such medications should be discontinued three to five days prior to RAI administration. These drugs generally can be resumed 3 to 10 days following treatment, or earlier, if clinically necessary (Table 2).
Pretreatment with propylthiouracil (PTU), with discontinuation up to one week prior to treatment, may increase the failure rate of radioiodine treatment (37). PTU interferes not only with iodine organification, but also may cause an iodide diuresis (38). For this reason, some have advocated higher doses (e.g., increase by 25%) for patients receiving antithyroid medications shortly before or after RAI treatment (39). Compared with PTU, pretreatment with methimazole may have a lesser effect on the failure rate of RAI treatment (40). Several prospective studies, where patients were randomized to no pretreatment with anti-thyroid drugs versus pretreatment with methimazole up to four to six days prior to RAI administration, found no significant differences in the success rate or the time to therapeutic response (41,42). The adverse effect of antithyroid
Table 2 Preparing Hyperthyroid Patients for Radioactive Iodine Treatment
Withdraw drugs which may interfere with RAI treatment: antithyroid medications for at least three days, multivitamins for one week, over-the-counter medications (expectorants, topical iodine, kelp, agar, potassium iodide solutions) for 2-3 weeks or longer depending on the iodine content, radiographic contrast agents for 4 weeks, and amiodarone for at least three to six months.
Review results from previous biochemical tests, RAI uptake measurements, and thyroid scintiscans. Confirm the appropriateness of treatment and treatment dose.
Obtain written informed consent. Provide verbal and written instructions.
Consider pretreatment with beta blockers for symptomatic control. Beta blockers may be continued during treatment.
Patients who have the potential to become pregnant should undergo pregnancy testing. If history indicates pregnancy is impossible, testing may be omitted at physician's discretion.
Breastfeeding patients should be instructed to stop for at least two days prior to treatment. Patients must be instructed not to resume breastfeeding until the birth of their next child.
Patient identity must be confirmed immediately before treatment in accordance with institutional requirements.
Abbreviation: RAI, radioactive iodine.
medications on RAI treatment efficacy may be more significant for toxic nodular goiters than for GD (43).
Patients should not eat solid foods or drink dairy products for at least two hours before and after treatment. Water is advised, however, to reduce radiation exposure to the genitourinary tract. Multivitamins should be discontinued seven days prior to treatment. Low iodine diets for about one week prior to RAI treatment have also been advocated, although this has not been convincingly shown to improve response when RAI is used for the treatment of hyperthyroidism. Written informed consent should be obtained at the time of treatment. Informed consent should include a review of the disease, the rationale for treatment, treatment alternatives, potential side effects and outcomes, and the need for follow-up, in addition to radiation precautions, which should be provided both verbally and in written form. Patients with GD should be counseled regarding the risks of ophthalmopathy. The prescribed activity should be verified in a dose calibrator and the patient's identity should be confirmed immediately prior to treatment.
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