Thyroid hormone therapy. What, when, and how much

Levothyroxine and insulin requirement in autoimmune polyglandular type 3 syndrome: a real-life study

PURPOSE

To evaluate factors influencing the insulin and levothyroxine requirement in patients with autoimmune polyglandular syndrome type 3 (APS-3) vs. patients with type 1 diabetes mellitus (T1DM) and autoimmune hypothyroidism (AH) alone, respectively.

METHODS

Fifty patients with APS-3, 60 patients with T1DM and 40 patients with AH were included. Anthropometric, clinical and biochemical parameters were evaluated in all patients. Insulin requirement was calculated in patients with APS-3 and T1DM, while levothyroxine requirement was calculated in APS-3 and AH.

RESULTS

Patients with APS-3 showed higher age (p = 0.001), age of onset of diabetes (p = 0.006) and TSH (p = 0.004) and lower total insulin as U/day (p < 0.001) and U/Kg (p = 0.001), long-acting insulin as U/day (p = 0.030) and U/kg (p = 0.038) and irisin (p = 0.002) compared to T1DM. Patients with APS-3 had higher waist circumference (p = 0.008), duration of thyroid disease (p = 0.020), levothyroxine total daily dose (p = 0.025) and mcg/kg (p = 0.006), triglycerides (p = 0.007) and VAI (p = 0.010) and lower age of onset of thyroid disease (p = 0.007) than AH. At multivariate analysis, levothyroxine treatment and VAI were associated with insulin and levothyroxine requirement in APS-3, respectively. VAI was independently associated with insulin requirement in T1DM. Circulating irisin levels were independently associated with levothyroxine requirement in AH.

CONCLUSION

Patients with APS-3 show lower insulin requirement and higher levothyroxine requirement than T1DM and AH alone, respectively. Levothyroxine treatment and VAI affect insulin and levothyroxine requirement, respectively, in APS-3. In T1DM, adipose tissue dysfunction, indirectly expressed by high VAI, is associated with an increased insulin requirement, while circulating irisin levels influence the levothyroxine requirement in AH.

Levothyroxine: therapeutic use and regulatory issues related to bioequivalence

Levothyroxine is the overwhelming choice of clinicians for the treatment of hypothyroidism and for the suppression of goitre and thyroid nodules in selected cases. The monitoring of serum levels of thyroid stimulating hormone is necessary for appropriate dosage adjustment of levothyroxine. Levothyroxine has a narrow therapeutic index: both underdosage (subclinical hypothyroidism) and excessive dosage (subclinical hyperthyroidism) are associated with adverse symptoms and pathophysiological effects and are to be avoided. The consequent necessity for careful titration of doses has had an impact on the issue of switchability, or bioequivalence, of the various marketed levothyroxine products. In this article, the basis for concern about currently accepted standards of the FDA for pharmacological bioequivalence are examined in the context of levothyroxine. The history and status of the recent request by the FDA for a new drug application for all levothyroxine products, and its impact on the market leader Synthroid, is also discussed.

Exaggerated levothyroxine malabsorption due to calcium carbonate supplementation in gastrointestinal disorders

OBJECTIVE

To describe a patient with primary hypothyroidism in whom ingestion of levothyroxine with calcium carbonate led to markedly elevated serum thyrotropin concentrations.

CASE SUMMARY

A 61-year-old white woman with primary hypothyroidism, systemic lupus erythematosus, celiac disease, and history of Whipple resection for pancreatic cancer was euthyroid with levothyroxine 175-188 micrograms/d. After taking a high dose of calcium carbonate (1250 mg three times daily) with levothyroxine, she developed biochemical evidence of hypothyroidism (thyrotropin up to 41.4 mU/L) while remaining clinically euthyroid. Delaying calcium carbonate administration by four hours returned her serum thyrotropin to a borderline high concentration (5.7 mU/L) within a month. Serum concentrations of unbound and total thyroxine and triiodothyronine tended to decrease, but remained borderline low to normal while the patient concomitantly received levothyroxine and calcium carbonate.

DISCUSSION

Concomitant administration of levothyroxine and calcium carbonate often results in levothyroxine malabsorption. While in most patients the clinical consequences of this interaction, even with prolonged exposure, are relatively small, overt hypothyrodism may develop in patients with preexisting malabsorption disorders. However, as the current case illustrates, the clinical manifestations of the initial levothyroxine deficit may not always be apparent and, of all usual laboratory thyroid function tests, only thyrotropin measurement will reliably uncover the exaggerated levothyroxine malabsorption.

CONCLUSIONS

Decreased absorption of levothyroxine when given with calcium carbonate may be particularly pronounced in patients with preexisting malabsorption disorders. Once recognized, a change in drug administration schedule usually minimizes or eliminates this interaction.

Hormonal profile of infertile Makkans

Male factor infertility, being a complex and heterogeneous disorder, precludes any reliance on a single laboratory test and requires broad spectrum assessment. Sociobiological factors also influence the parameters. In this context we examined serum concentrations of nine hormones in infertile and fertile male Makkans. Infertility was implicated in 21% of the population with correlated abnormalities of gonadotrophins, thyroid, thyroid stimulating hormone (TSH), and testosterone. Hypothyroidism was established in 35% and hyperthyroidism in 14% of the infertile population, where 28% of thyroid abnormality constituted an independent infertile group. Hyperprolactinaemia associated with low levels of luteinizing hormone (LH) and testosterone signifies a cluster of 28%, while 14% of testosterone deficiency alone was causal for infertility. However, infertility in 9% of the patients examined might have been psychogenic in nature. We present a responder panel based on cluster analysis.

Diagnosis and management of hypothyroidism in pregnancy

Hypothyroidism is not a common occurrence in pregnancy, but it is important that nurse practitioners recognize it early. Complications of hypothyroidism in pregnancy are pregnancy-induced hypertension, preeclampsia, abruptio placentae, low birth weight and stillbirth, and fetal distress in labor. Careful monitoring of pregnant women for hypothyroidism and correction with levothyroxine therapy can prevent these complications. During pregnancy, the thyroxine needs of women with hypothyroidism are increased, and their dosage of levothyroxine should be individualized. Nurse practitioners can provide holistic care to the woman with hypothyroidism to ensure optimal maternal and fetal health.

Management of Thyroxine Therapy During Pregnancy

OBJECTIVE

To review the management of thyroxine (T4) therapy in pregnant patients with hypothyroidism.

METHODS

The results of pertinent published studies are summarized, and practical recommendations are presented.

RESULTS

The conditions for which T4 therapy is administered during pregnancy are the same as those in nonpregnant patients: hypothyroidism, thyrotropin or thyroid-stimulating hormone (TSH) control after surgical treatment of thyroid cancer, and, in selected patients, suppression treatment for postsurgical thyroid remnants, thyroid nodules, or goiter. Untreated hypothyroidism during pregnancy can potentially cause adverse effects in both mother and fetus. Up to 75% of T4-treated women with hypothyroidism require higher doses of T4 during pregnancy than before or after conception, to maintain serum TSH levels in the normal range. Otherwise, in a substantial percentage of these women, subnormal serum free T4 levels, TSH elevations >20 microIU/L, or both will develop. The mean T4 dose needed to correct hypothyroidism during pregnancy is about 150 microg/day, but individual dose requirements vary widely.

CONCLUSION

The increment in T4 dose needed to normalize an increased TSH level in women taking T4 can be estimated from the serum TSH concentration during pregnancy. Increased TSH levels can appear as early as 4 to 8 weeks of gestation or as late as the third trimester. Although the optimal schedule is uncertain, assessing the TSH once each trimester seems reasonable. After pregnancy, the T4 dose should be reduced to the preconception level, and postpartum reassessment should be done at 6 to 12 weeks.

Advances in the management of patients with thyroid disease

Discoveries related to thyroid immunology, especially concerning the thyroid-stimulating hormone (TSH) receptor, may facilitate new immunologic approaches to the therapy of Graves' disease and the thyroiditis syndromes. Advances in genetics are being applied to the thyroid hormone resistance syndromes and papillary and medullary carcinomas. The development of ever more sensitive TSH assays has led to the detection of subclinical thyroid disease, which has special implications for the sick and elderly patients. Sensitive TSH assays also allow more precise titration of levothyroxine (T4) dosages, especially for patients with a past history of thyroid cancer. Evidence continues to accumulate suggesting that postmenopausal women on T4 doses that suppress the TSH level below 0.1 ulU/mL have lower bone mineral density than matched patients with healthy TSH levels. Also, pregnant hypothyroid women need higher T4 doses to normalize the TSH levels. In the evaluation of thyroid nodules, fine-needle aspiration biopsy is the single most definitive modality in selecting the patients for surgery. Scintigraphy provides a complimentary role, especially in defining autonomously functioning thyroid adenomas (AFTA), because these should not be treated with T4 suppression. Ultrasound-guided needle biopsy is occasionally helpful with nodules that are difficult to palpate. Concern for possible tracheal compression after treatment of toxic multinodular goiter with large doses of radioactive iodine (I-131) in the range of 50 to 150 mCi (1.85 to 5.5 GBq) does not seem warranted. Work, primarily out of Italy, suggests AFTA can be ablated with repeat ethanol injections. Residual tissues after thyroidectomy for differentiated carcinoma can be "stunned" by tracer doses of 131I greater than 3.0 mCi (111 MBq), which diminishes the uptake and effectiveness of a subsequent therapy dose. Positron emission tomograph, imaging with thallium-201, and Technetium 99m Sestamibi can identify a small number of patients shown to have metastases from differentiated thyroid carcinoma by increasing thyroglobulin levels in the absence of 131I uptake. Several groups have recently advocated treating such patients empirically with 131I.