Effect of pretreatment with carbimazole on early outcome following radio-iodine (131I) therapy

Efficacy of methimazole before the administration of radioactive iodine in the management of Graves' disease: a systematic review and meta-analysis

BACKGROUND

The efficacy of anti-thyroid drugs in conjunction with radioactive iodine therapy in the management of Graves' disease is still controversial.

OBJECTIVE

To compare the efficacy of pretreatment with methimazole before the administration of radioactive iodine for the treatment of Graves' disease.

DESIGN AND SETTING

A systematic review and meta-analysis was conducted at a teaching/tertiary hospital in Ibadan, Nigeria.

METHODS

A systematic search of the PubMed, Embase, Cochrane Library, and Web of Science databases was performed from inception to December, 2021.

RESULTS

Five studies with 297 participants were included. There was no difference in the risk of persistent hyperthyroidism when radioactive iodine was used in conjunction with methimazole compared with when radioactive iodine was used alone (relative risk: 1.02, 95% confidence interval, CI: 0.62-1.66; P = 0.95, I2 = 0%). Subgroup analysis based on the duration between discontinuation of methimazole and the administration of radioactive iodine showed a lower risk of persistent hyperthyroidism when methimazole was discontinued within 7 days before radioactive iodine use, although this did not reach statistical significance (risk ratio: 0.85, CI: 0.28-2.58).

CONCLUSIONS

The use of methimazole before radioactive iodine administration was not associated with an increased risk of persistent hyperthyroidism. Concerns about medication toxicity and adverse effects should be considered when clinicians make decisions on combination therapies for the treatment of Graves' disease.

PROSPERO REGISTRATION

CRD42020150013, https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=150013.

Observational Study on Outcomes after Radioiodine Ablation in Hyperthyroid Patients

INTRODUCTION

Radio-active Iodine (RAI) is a safe, definitive, and cost-effective modality of treatment that is used as the first line of treatment for Graves' hyperthyroidism by most endocrinologists. Very few reports are available from India, observational follow-up data is needed to determine the meaningful prognostic outcomes of RAI ablation in the Indian population.

AIMS

To study the outcomes in hyperthyroid patients undergoing RAI ablation.

MATERIALS AND METHODS

This observational cohort study was conducted at Department of Endocrinology at Indraprastha Apollo Hospital, New Delhi. A total of 82 hyperthyroid patients who underwent RAI ablation between June 2014 to June 2018 were enrolled. RAI dose was calculated arbitrarily in most cases; often by an empirical fixed dose based on the goiter size and RAIU. The patients were reviewed at 1, 3 and 6 months post-RAI ablation. During follow-up, along with a detailed clinical examination, free T4, free T3 and TSH were checked.

RESULTS

The dose of I-131 varied from 6 mCi to 14 mCi. Most of the patients were given RAI in the dose of 7.1-10 mci. About 63.4% of patients achieved hypothyroidism in 6 months, 6.1% in 1 month, 37.8% in 3 months, and 19.5% in 6 months. Gender, age, etiology of hyperthyroidism, baseline thyroid function, goiter, and ophthalmopathy did not affect outcomes after RAI ablation. Those who were not treated with antithyroid drugs prior to RAI therapy were found to have higher rates of conversion to a hypothyroid state.

CONCLUSION

RAI can be given safely as the first line of treatment in Graves' disease and antithyroid drug naïve patients respond better to therapy.

Effect of thyroid volume on radioiodine therapy outcome in hyperthyroid cats

Radioiodine therapy is commonly used in hyperthyroid cats and has a high success rate, ranging from 85-95%. As in humans, thyroid volume has been reported to influence radioiodine therapy outcome in hyperthyroid cats. The purpose of this study was to relate total thyroid volume, calculated by a newly constructed formula for feline patients (0.438 × length × width²), to the outcome of radioiodine therapy. To search for a correlation between total thyroid volume and therapy outcome, 167 hyperthyroid cats were included. Patients were categorised according to the administered radioiodine dose and therapy outcome. Our analysis did not show a significant relationship between an increasing total thyroid volume and the odds for a final low total thyroxine concentration (TT4; P = 0.3930) or a final hyperthyroid outcome (P = 0.0901). A significant relationship was found for an increase in the odds for a final low TT4 outcome with an increase in the number of foci detected on the pertechnetate thyroid scan (P = 0.0238). This was not true for a final hyperthyroid outcome (P = 0.7435). The number of detected foci was also significantly associated with the total thyroid volume (P = 0.0006). Findings indicated that the presence of multiple affected foci influences therapy outcome towards a low TT4 outcome. Bilateral hyperthyroidism and its potential effect on a final low TT4 outcome should therefore be addressed when informing owners of the possible outcomes of radioiodine therapy for their cat.

Long-term carbimazole pretreatment reduces the efficacy of radioiodine therapy

INTRODUCTION

Data from several studies suggest that pretreatment with antithyroid drugs (ATD) before (131)I increases the risk of treatment failure. This effect has been demonstrated more consistently with propylthiouracil than with carbimazole (CMZ) or methimazole (MMI). Men with Graves' disease (GD) have a lower rate of remission with (131)I compared to women and the impact of long-term ATD pretreatment on the success of (131)I is unknown. The objective of our study was to compare the efficacy of fixed doses of radioiodine between patients with and without long-term CMZ pretreatment.

MATERIALS AND METHODS

We performed a retrospective study on 335 male patients with GD treated with (131)I from 1998 to 2008. 148 patients had been pretreated with CMZ, and the remaining 187 patients received (131)I without pretreatment. We compared the success rate of a single dose of (131)I, between patients with and without long-term CMZ pretreatment.

RESULTS

The success rate of a single dose of (131)I was significantly higher in patients without pretreatment than in patients who were pretreated with CMZ (91.4% vs. 82.3%, P = 0.01). The rate of hypothyroidism in the first 6 months after (131)I therapy was significantly higher in patients without pretreatment (55.1% vs. 44.6%, P = 0.05). There was also a trend for higher cumulative rate of hypothyroidism at last follow-up in nonpretreated patients (78.1% vs. 69.7%).

CONCLUSION

Male patients with Graves' hyperthyroidism pretreated with CMZ have lower efficacy with 131I therapy compared to nonpretreated patients. CMZ pretreatment given for a prolonged period reduces the efficacy of (131)I therapy.

Radioiodine therapy in patients with Graves' disease and the effects of prior carbimazole therapy

The use of radioiodine as the first line of treatment in Graves' disease is restricted in India because of its limited availability and an unrealistic risk perception associated with it. Additionally, the effectiveness of radioiodine ablation in Graves' disease is influenced by many factors. Prior medical antithyroid therapy is one such important factor.

AIMS

To analyze the efficacy of low dose radioiodine therapy (5 mCi) in treatment of naive patients of Graves' disease in comparison to that in which it was already primed with an antithyroid drug, carbimazole.

SETTINGS AND DESIGN

A non-randomized, interventional study conducted in the Department of Medicine and Endocrinology of a tertiary care institute in South India.

MATERIALS AND METHODS

The study had two groups; Group A (36 treatment naive, uncomplicated Graves' disease patients) and B (34 Graves' disease patients on carbimazole prior to radioiodine therapy). Both groups had baseline clinical, biochemical evaluation and were reassessed at 3 and 6 months for evaluating the clinical status for possible documentation of cure.

RESULTS

The cure rate was 61.1% in drug naive group and 58.8% in pretreated group at 6 months following radioiodine (P = 0.845). Higher baseline 999m technicium (99m Tc) uptake, male gender, BMI and higher baseline free thyroxine (fT4) level predicted treatment failure following radioiodine therapy.

CONCLUSIONS

Administration of carbimazole prior to low dose radioiodine therapy does not alter the efficacy of radioiodine. Low fixed dose (5 mCi) of radioactive iodine may be a safe and effective primary therapeutic option in Graves' disease patients pretreated with antithyroid drugs.

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.

Two-day thionamide withdrawal prior to radioiodine uptake sufficiently increases uptake and does not exacerbate hyperthyroidism compared to 7-day withdrawal in Graves' disease

The appropriate period of antithyroid drug (ATD) discontinuation before radioiodine therapy is the most critical problem in Graves' disease patients under going treatment with ATD. To determine the optimal period that does not alter the outcome of radioiodine therapy or exacerbate hyperthyroidism, we compared serum FT4 levels at radioiodine uptake (RAIU) and therapy outcomes between a 2-day withdrawal group and 7-day withdrawal group. We prospectively recruited 43 patients for the 2-day withdrawal protocol and retrospectively reviewed 49 patients treated with radioiodine following the protocol of 7-day withdrawal. There was no significant difference in RAIU between the 2 groups. The mean serum FT4 level measured on the first day of 24-h RAIU of the 7-day group was significantly higher than that in the 2-day group. There were no significant differences in the outcomes at each point (6 months, 1 year, and 2 years after therapy) between the 2 groups. Our results indicated that withdrawal of ATD for 2 days is superior to 7 days in that 2 days discontinuation did not exacerbate hyperthyroidism. In order to prevent serum thyroid hormone increase after ATD withdrawal and radioiodine therapy, a 2-day ATD withdrawal period before radioiodine therapy may be useful for high-risk patients such as the elderly and patients with cardiac complications. We believe that the 2-day ATD withdrawal method may be useful for patients undergoing treatment with ATD who are to undergo radioiodine therapy.

The effect of methimazole on cure rates after radioiodine treatment for Graves' hyperthyroidism: a randomized clinical trial

Forty-two newly diagnosed patients with Graves' hyperthyroidism were randomly assigned to receive 131I therapy after pretreatment with methimazole (21) or beta-blocker alone (21) and prospectively evaluated, to determine possible effects of methimazole on 131I treatment outcome. After randomization, 8 patients were excluded from the study (5 from pretreatment group and 3 from nonpretreatment group). Radioactive iodine (baseline dose 15 mCi, adjusted for goiter size and/or 131I uptake) was administered after pretreatment with methimazole (30 mg initial dose for at least 2 months and stopped 6 days before treatment) and beta-blocker or pretreatment with beta-blocker alone (atenolol 50-100 mg/d). All but one patient in each group became hypothyroid. A similar length of time was required by both groups to achieve hypothyroidism (112 days, [95% confidence interval [CI] = 28 to 196 days) in the pretreated group and 106 days, [95% CI = 45 to 167 days] in nonpretreated patients). Free thyroxine (T4) normalized 44 +/- 39 days after therapy in the nonpretreated group and 35 +/- 30 days in the pretreated group (p = 0.57) and decreased to subnormal levels 80 +/- 70 days in nonpretreated and 65 +/- 32 days in pretreated patients (p = 0.46). We conclude that pretreating patients with methimazole before radioactive iodine therapy does not interfere with the final outcome. Similar cure rates and time required to achieve hypothyroidism after radioiodine were observed when patients were pretreated with methimazole compared to nonpretreated patients.

Radioiodine therapy in Graves' disease patients with large diffuse goiters treated with or without carbimazole at the time of radioiodine therapy

We sought to ascertain how high the success rates of radioiodine therapy are for Graves' disease patients with large diffuse goiters when aiming for a constant absorbed dose of 250 Gy. Thirty-six patients with a thyroid volume of 50-110 mL were evaluated for changes in thyroid function and appearance 3, 6, and 12 months after radioiodine therapy. Success was defined as definitive elimination of hyperthyroidism following therapy (hypothyroidism corrected with thyroxine on diagnosis); failure as persistent/recurrent hyperthyroidism after 12 months. Overall success rate was 50%. However, a subgroup of 20 patients without simultaneous carbimazole (carbimazole-off) showed a highly significantly larger success rate (85%) than the 16 patients with simultaneous carbimazole (carbimazole-on) at the time of radioiodine therapy (6.3%, p < 0.000005). Successful cases showed a significantly higher volume reduction after radioiodine than failures (75.5% vs. 35.4%, p < 0.00005). Stepwise logistic regression showed that therapy failure was related to administration of carbimazole during radioiodine therapy (p < 0.0250 and absorbed dose (p < 0.05), but not thyroid function (free triiodothyronine [FT3] and free thyroxine [FT4]), initial thyroid volume or thyrotropin-receptor antibody (TRAb) value. However, a significant correlation of therapy success to absorbed dose (r = 0.69, p < 0.005) could be shown only for carbimazole-off patients, but not for the others. Finally, multivariate factor analysis consistently showed that therapy success was correlated only to absorbed dose and antithyroid drugs, not to initial thyroid volume, TRAb value, or thyroid function. Thyroid volume per se is not responsible for the lower success rate in Graves' disease patients with large goiters because even a comparable group of 32 Graves' disease patients with small thyroid glands (< or =20 mL) and without simultaneous carbimazole showed a success rate of 87.5%. The high failure rate in the carbimazole-on patients (absorbed dose comparable to carbimazole-off) is due to the simultaneous administration of carbimazole. Therefore, if clinically feasible, we recommend discontinuing carbimazole at least one day before beginning radioiodine therapy.

Success rate of radioiodine therapy in Graves' disease: the influence of thyrostatic medication

There is controversy whether simultaneous thyrostatic medication influences the outcome of radioiodine (131I) therapy in Graves' disease by reducing the absorbed energy dose of 131I when delivering a standard dose. We therefore sought to ascertain whether the outcome of ablative 131I therapy is in any way affected by simultaneous thyrostasis (carbimazole) by aiming for a constant absorbed dose of 200-250 Gy. We prospectively studied 207 patients with Graves' disease (106 with and 101 without simultaneous carbimazole at the time of 131I therapy). All patients were reexamined 3, 6, and 12 months after 131I therapy. The 101 nonthyrostatic patients showed a highly significantly greater success rate (93%) than the 106 thyrostatic patients (49%). Stepwise logistic regression demonstrated that failure was related to the administration of carbimazole during 131I therapy (P < 0.00005) and the absorbed dose (P < 0.025), but was not related to free T3, free T4, TSH receptor antibodies, or thyroid volume. The success rate was 100% in 93 nonthyrostatic patients with absorbed doses of 200 Gy or more, but was only 12.5% (1 of 8) for absorbed doses less than 200 Gy. Correlation between success and absorbed dose was significantly higher for nonthyrostatic than for thyrostatic patients (r = 0.93 vs. r = 0.24). Sixteen patients who discontinued thyrostasis 1-3 days before 131I therapy showed 94% successes. Simultaneous thyrostasis is the decisive factor against a successful 131I therapy even if the significantly reduced 131I uptake/half-life values under thyrostasis are compensated with a higher delivered dose to ensure a comparable absorbed dose, possibly due to the additionally effective radioprotective properties of carbimazole. Therefore, if clinically feasible, we recommend discontinuing thyrostasis at least 1 day before beginning 131I therapy, because even in hyperthyroid nonthyrostatic patients the success rate was 100%.

Time interval between the last dose of propylthiouracil and I-131 therapy influences cure rates in hyperthyroidism caused by Graves' disease

PURPOSE

To examine the effects of propylthiouracil (PTU) pretreatment on the outcome of initial I-131 therapy for Graves' disease.

DESIGN

A retrospective chart review was done.

PATIENTS AND METHODS

The authors studied 106 patients in an outpatient nuclear medicine setting who were given initial I-131 therapy for Graves' disease from September 1989 to March 1993 and followed for at least 6 months after therapy. These patients were divided into groups based on whether they had ever received PTU or, if they had received PTU, the length of time between the last dose of PTU and the I-131 therapy dose. Measured failure rates of initial I-131 therapy were based on recurrent or continued hyperthyroidism.

RESULTS

Treatment failure rates increased markedly from 2.5% in non-PTU-treated patients (n = 80) to 23.1% (n = 26) in patients pretreated with PTU (P = 0.003). Although not significant, two PTU-pretreated subgroups showed a trend toward increased failure rates. The failure rate was 15.4% (n = 13) in patients whose last dose of PTU was 7-14 days before I-131 therapy, and it increased further to 30.8% (n = 13) in patients whose last dose of PTU was within 1 week of I-131 therapy.

CONCLUSIONS

PTU pretreatment within 2 weeks of I-131 treatment is a strong independent risk factor in failure rates after initial I-131 therapy in patients with Graves' disease. Patients should be free of PTU for 2 weeks before I-131 therapy if they are able to tolerate it, otherwise the dose of I-131 may need to be adjusted upward to diminish the risk that the initial I-131 therapy will fail.

A Clinical Guide to the Management of Graves’ Disease with Radioactive Iodine

More than 50 years have passed since radioactive iodine (RAI) was initially demonstrated as a therapeutic modality for the treatment of Graves' Disease. Today, more than a million patients have been treated with RAI. RAI is considered safe and highly effective. Its side-effect profile, ease of administration, and relative cost make RAI the treatment of choice for Graves' Disease of thyroidologists in this country. Questions continue to be raised as to which patients will benefit most from RAI therapy. Marked differences still exist between the practice preferences of thyroidologists as to whom, when, and how to treat with RAI. Factors that influence patient selection for RAI include age, the presence of pre-existing ophthalmopathy, lifestyle, history of previous treatment failure, and goiter size. Treatment goals, dosimetry, use of thionamides prior to therapy, safety recommendations following therapy, and prophylactic therapy with glucocorticoids for patients with ophthalmopathy highlight are some of the controversial issues facing the endocrinologist treating Graves' Disease with RAI. This symposium article reviews the current management of Graves' Disease with RAI.

Low-dose radioiodine given six-monthly in Graves' disease

Experience using low-dose radioiodine given six-monthly instead of yearly in hyperthyroid patients with Graves' disease is reported. One hundred and thirty-five patients have been treated over a three-year period with 74 MBq (2 mCi) doses of 131I. Thirty-eight percent were controlled with a single dose. Those patients requiring more than one dose were treated with a further 74 MBq (2 mCi) 131I at six-monthly intervals until euthyroid. Using this approach, 46% were euthyroid one year after starting treatment, and 75% were euthyroid at two years. The incidence of hypothyroidism following treatment was 2.2% at one year, with a yearly incidence thereafter of 4-6%. Six-monthly scheduling of low-dose radioiodine in Graves' disease can reduce the time taken to become euthyroid, compared with conventional yearly low-dose treatments. Further follow up is required to confirm the present low incidence of hypothyroidism following treatment.