Radionuclide administration to nursing mothers: mathematically derived guidelines

Medications and Breast-Feeding: A Guide for Pharmacists, Pharmacy Technicians, and other Healthcare Professionals Part III

Objective:

To provide a guide for practicing pharmacists, pharmacy technicians, and other healthcare professionals so that they are able to counsel and advise breast-feeding mothers and fellow healthcare professionals on the safety and use of antiinfectives, vaccines, antiepileptics, benzodiazepines, psychotherapeutic drugs, and radiopharmaceuticals during breast-feeding.

Data Sources:

Primary texts used by the breast-feeding community ( Medications and Mothers' Milk, Drugs in Pregnancy and Lactation, Drugs and Human Lactation) were searched, as well as Micromedex, MEDLINE, PubMed, EMBASE, and EMBASE2 (1984–February 2004).

Study Selection/Data Extraction:

Multiple sources were used wherever available to validate the data, and primary articles were used to verify all tertiary source information. Search terms included breast-feeding, lactation, nursing, and medications, as well as specific drug names.

Data Synthesis:

Concerns regarding medication use during breast-feeding have caused mothers to either discontinue nursing or not take necessary medications. Complete avoidance of medications or cessation of breast-feeding is often unnecessary. Although there are drugs that can be harmful to nursing infants, breast-milk concentrations of most drugs are insufficient to cause any harm.

Conclusions:

Having objective and reliable information on medications enables pharmacists, pharmacy technicians, other healthcare providers, and mothers to make educated decisions regarding drug therapy and breast-feeding.

Differentiation of postpartum Graves' thyrotoxicosis from postpartum destructive thyrotoxicosis using antithyrotropin receptor antibodies and thyroid blood flow

BACKGROUND

Postpartum thyroid dysfunction occurs in approximately 5-10% of women in the general population within one year of delivery. Differentiation of postpartum Graves' thyrotoxicosis (PPGr) from postpartum destructive thyrotoxicosis (PPDT) is essential because of the difference in treatment measures between the two. However, it is sometimes difficult because radioactive iodine uptake is contraindicated when patients are lactating. We examined the usefulness of determining the time of onset postpartum and measurement of antithyrotropin (anti-TSH) receptor antibodies and thyroid blood flow.

METHODS

Forty-two patients with newly developed thyrotoxicosis after delivery were examined: 18 had Graves' disease and 24 had destructive thyrotoxicosis. Serum free thyroxine (fT4), free triiodothyronine (fT3), and TSH were measured by chemiluminescent immunoassays. Anti-TSH receptor antibodies (TRAb), antithyroglobulin antibodies (TgAb), and antithyroid peroxidase antibodies (TPOAb) were measured by the Elecsys electrochemiluminescence immunoassay. Thyroid volume and blood flow (TBF) were measured quantitatively by color flow Doppler ultrasonography.

RESULTS

Onset of thyrotoxicosis was distributed from 2 to 12 months postpartum. Twelve (85.7%) of 14 patients who developed thyrotoxicosis at three months or earlier after delivery had PPDT. On the other hand, all 11 patients who developed thyrotoxicosis at 6.5 months or later had PPGr. All patients with PPGr had positive TRAb (14.9±14.9 IU/L, mean±standard deviation (SD)) and all patients with PPDT had negative TRAb (0.1±0.3 IU/L, p<0.0001). Fifteen (83.3%) of 18 PPGr patients had high TBF of more than 4.0% (8.9±4.4), and all PPDT patients had low TBF of <4.0% (1.6±1.0, p<0.0001). The fT3/fT4 ratio was higher in PPGr (64.0±23.9) than in PPDT (38.9±13.1, p<0.0002), but absolute values overlapped between the two.

CONCLUSION

Early onset of thyrotoxicosis postpartum was associated mainly with PPDT, and a late onset was suggestive of PPGr. Positive TRAb and high TBF >4.0% are indicators of postpartum onset of Graves' disease.

Quantitative measurement of thyroid blood flow for differentiation of painless thyroiditis from Graves' disease

OBJECTIVE

Differentiation between destruction-induced thyrotoxicosis and Graves' thyrotoxicosis is important for selection of proper therapy. It is, however, often difficult to make this distinction without measurement of radioactive iodine uptake. We investigated the possibility that assessment of thyroid blood flow would allow differentiation between the two entities.

PATIENTS AND MEASUREMENTS

One hundred and fourteen untreated patients with thyrotoxicosis (56 Graves' disease, 28 painless thyroiditis, 30 subacute thyroiditis) and 25 normal controls were examined. Serum levels of freeT4 (FT4), freeT3 (FT3) and TSH were measured by chemiluminescent immunoassay, and anti-TSH receptor antibodies (TSH-binding inhibitory immunoglobulin, TBII) were measured by enzyme-linked immunosorbent assay. Thyroid volume and blood flow (TBF) were measured quantitatively by ultrasonography.

RESULTS

TBF was significantly higher in Graves' disease (mean +/- 1SD: 14.9 +/- 6.4%, P < 0.0001) than in painless thyroiditis (0.8 +/- 0.5%), subacute thyroiditis (0.9 +/- 0.7%) and in normal controls (0.8 +/- 0.5%). All patients with Graves' disease had TBF values of more than 4% and all patients with painless thyroiditis and subacute thyroiditis had TBF values less than 4%. TBF values significantly correlated with values of radioactive iodine uptake (RAIU) either at 3 h (r = 0.492, P < 0.01) or 24 h (r = 0.762, P < 0.001) within the Graves' disease and painless thyroiditis groups. There was no relationship between TBF values and thyroid volumes or values of TBII in the Graves' disease group. All patients with Graves' disease had positive TBII of 15% or more. Three of 28 patients with painless thyroiditis and one of 30 patients with subacute thyroiditis had positive TBII.

CONCLUSION

TBF was quantitatively measured by power Doppler ultrasonography and was more effective than TBII for differentiation between destruction-induced thyrotoxicosis (painless or subacute thyroiditis) and Graves' thyrotoxicosis. TBF values of less than 4% in untreated thyrotoxic patients are laboratory signals of destruction-induced thyrotoxicosis and if these are determined, the radioactive iodine uptake test can be omitted for differential diagnosis of these two types of thyrotoxicosis.

Radioiodine fallout and breast-feeding

The rationale for suspension of breast-feeding after exposure to radioiodine in fallout is presented.

Postpartum thyroiditis and autoimmune thyroiditis in women of childbearing age: recent insights and consequences for antenatal and postnatal care

Postpartum thyroiditis is a syndrome of transient or permanent thyroid dysfunction occurring in the first year after delivery and based on an autoimmune inflammation of the thyroid. The prevalence ranges from 5-7%. We discuss the role of antibodies (especially thyroid peroxidase antibodies), complement, activated T cells, and apoptosis in the outbreak of postpartum thyroiditis. Postpartum thyroiditis is conceptualized as an acute phase of autoimmune thyroid destruction in the context of an existing and ongoing process of thyroid autosensitization. From pregnancy an enhanced state of immune tolerance ensues. A rebound reaction to this pregnancy-associated immune suppression after delivery explains the aggravation of autoimmune syndromes in the puerperal period, e.g., the occurrence of clinically overt postpartum thyroiditis. Low thyroid reserve due to autoimmune thyroiditis is increasingly recognized as a serious health problem. 1) Thyroid autoimmunity increases the probability of spontaneous fetal loss. 2) Thyroid failure due to autoimmune thyroiditis-often mild and subclinical-can lead to permanent and significant impairment in neuropsychological performance of the offspring. 3) Evidence is emerging that as women age subclinical hypothyroidism-as a sequel of postpartum thyroiditis-predisposes them to cardiovascular disease. Hence, postpartum thyroiditis is no longer considered a mild and transient disorder. Screening is considered.

Artifacts, anatomical and physiological variants, and unrelated diseases that might cause false-positive whole-body 131-I scans in patients with thyroid cancer

The whole body 131-I scan remains an important component in the postoperative treatment of patients with well-differentiated thyroid cancer. Because normal thyroid tissue remnants and residual or metastatic foci of well-differentiated thyroid cancer have the unique ability to concentrate, organify, and store 131-I, the whole body scan provides a depiction of those tissues that can be ablated with therapeutic doses of 131-I. Over time, it has become obvious that the whole body scan may also reveal foci of 131-i uptake owing to a wide variety of other causes. We provide a detailed pathophysiological classification of the artifacts, anatomic and physiological variants, and nonthyroidal diseases that may give rise to false-positive whole body scans in postoperative patients with thyroid cancer. These include ectopic foci of normal thyroid tissue; nonthyroidal physiological sites (eg, choroid plexus, salivary glands, gastric mucosa, urinary tract); contamination by physiological sections; ectopic gastric mucosa; other gastrointestinal abnormalities; urinary tract abnormalities; mammary abnormalities; serous cavities and cysts; inflammation and infection; nonthyroidal neoplasms; and currently unexplained causes. This article also provides a detailed review of the widely scattered English language literature in which these phenomena were originally described.

Iodine-131 elimination from breast milk: a case report

This case report describes the management of a breastfeeding mother who had been given radioactive iodine and technetium for diagnosis of thyroid disease. The mother requested to submit weekly milk samples for monitoring of radioactivity. Once activity fell below measurable counts, the mother resumed lactation.

Determining the breast-feeding interruption schedule after administration of 123I-iodide

Radioactivity after administration of 123I-sodium iodide was measured in breast milk samples obtained from a patient with postpartum thyroiditis. The breast milk was collected over 93 h during the infant's regular feeding times. The radioactivity in the breast milk was calculated with a 123I capsule of the same lot number as the standard source. 123I was excreted exponentially with an effective half-life of 5.5 h; 2.5% of the total radioactivity administered was excreted in the breast milk over the 93 h, 95% of which was excreted within the first 24 h, and 98.2% within 36 h. The first milk sample collected at 7 h after administration of the radiopharmaceutical contained 48.5% of the total radioactivity excreted. We estimated the potential absorption of radioactivity to an infant's thyroid in uninterrupted breast-feeding to be 30.3 mGy. With a 24-hour interruption, the absorbed radioactivity would be 1.25 mGy; with a 36-hour interruption, it would be 0.24 mGy. According to our calculations, breast feeding should be curtailed for 36 h to reduce the infant's exposure to 123I radioactivity. By using a correction factor based on maximum radioactivity from another 123I capsule of the same lot, we were able to ascertain the appropriate protocol for our patient and establish a measurement method that can be applied in similar clinical situations.

Postpartum thyroid dysfunction

Four disorders of the postpartum period are associated with thyroid dysfunction. The most common is PPT. Although recovery from thyroid dysfunction often occurs in PPT, many patients eventually develop permanent hypothyroidism. Postpartum Graves' Disease is less common than PPT, but it is not unusual. Whereas antithyroid drugs are indicated for postpartum Graves' Disease, they are not useful in PPT. Although they are rare, lymphocytic hypophysitis and postpartum pituitary infarction are important entities because they cause deficiencies of many critical hormones. The autoimmune nature of PPT, postpartum Graves' disease, and lymphocytic hypophysitis highlights the unique effects of pregnancy on the immune system.

The excretion of radiopharmaceuticals in human breast milk: additional data and dosimetry

The amount of radioactivity excreted in breast milk following administration of 11 different radiopharmaceuticals, including technetium-99m labelled microspheres, pyrophosphate, diisopropyl-iminodiacetic acid (DISIDA) and sestamibi, has been measured. This report summarises the data collected from 60 patients. An effective decay constant for the series of samples from each patient was calculated from exponential curves fitted by least squares to the data. It is difficult to compare values from individual patients, since times of expression, volumes of milk and the activity administered are not uniform. In order to formulate reliable guidelines, we therefore calculated the total activity theoretically excreted in milk until complete decay of the radionuclide, which is usually higher than that actually measured over the actual period of collection. Of the various 99mTc compounds, pertechnetate clearly reaches the highest concentrations in breast milk. The wide variability of data from different patients who received the same radiopharmaceutical despite identical methods of sample collection and data processing confirms the impression gained from literature that transfer of radionuclides into milk varies greatly between individuals. Although we have calculated average values for each compound, very large standard deviations were obtained, and we believe that for radiation protection purposes, a "worst case" approach is the most appropriate. With new data available and the revision of ICRP recommendations, the guidelines applicable when radiopharmaceuticals are administered to breast-feeding mothers are reviewed. The effective dose resulting from close contact between patient and infant was included in these calculations. Breast feeding need not be interrupted after administration of 99mTc-DISIDA, -sulphur colloid, -gluconate and -methoxyisobutylisonitrile (MIBI). However, after administration of 99mTc-MIBI, close contact should be restricted. 99mTc-pyrophosphate and -microspheres require interruption periods of several hours. High activities of 99mTc-pertechnetate may require interruption longer than 2 days. For pertechnetate and 99mTc-labelled red blood cells, interruption of breast feeding with measurement of activity in expressed milk samples is recommended. Breast feeding is contra-indicated after administration of 67Ga and 131I. General guidelines regarding breast feeding after administration of radiopharmaceuticals are summarised.

Excretion of technetium 99m hexakismethoxyisobutylisonitrile in milk

The amount of radioactivity excreted in breast milk following the administration of technetium 99m hexakismethoxyisobutylisonitrile (99mTc-MIBI) to a patient referred for cold spot myocardial scintigraphy was determined. During the first 24 h after administration, only 41.2 kBq 99mTc (0.0084% of the injected dose) was excreted in 448 ml milk with the highest concentration of 0.49 kBq/ml in the first sample. The images obtained show a high concentration of 99mTc-MIBI in the lactating breasts contrary to the very small percentage excreted in the milk. Comparison with various recommendations regarding nursing after administration of radiopharmaceuticals seems to indicate that the administration of 99mTc-MIBI does not necessitate an interruption of breast-feeding.