Optimal daily levothyroxine dose in primary hypothyroidism: its relation to pretreatment thyroid hormone indexes

Article Abstract:

The use and effectiveness of thyroid hormone indexes, obtained at the time of the primary diagnosis of hypothyroidism, were evaluated as the means of establishing a pretreatment regimen of levothyroxine dosage for patients suffering from hypothyroidism. Hypothyroidism is a deficiency in the secretion of thyroid, characterized by an overall decrease in metabolic rate and physical activity. Persons suffering from hypothyroidism are prone to such symptoms as obesity, dry skin and hair, low blood pressure, slow pulse, sluggishness, goiter, and depressed muscular activity. Thyroid hormone indexes were tested as predictors of the most effective dose of levothyroxine sodium replacement in the treatment of primary hypothyroidism in a population of 156 persons suffering from primary hypothyroidism, ranging in age from 25 to 84 years. Levothyroxine sodium is closely related to thyroxine, the hormone produced by the thyroid gland, and is used in treating thyroid gland deficiencies. There is little information regarding dose maintenance guidelines in younger patients. In the elderly, levothyroxine replacement doses must be carefully regulated to avoid untoward side effects such as irregular heart beats, angina, or congestive heart failure. In the absence of data on the use of this drug in younger patients, the initial levothyroxine dose has been based on the judgment of individual physicians. This study indicates that the use of thyroid hormone indexes may provide a useful guide in establishing maintenance levothyroxine doses in subjects of all ages. Blood levels of thyroid stimulating hormone (TSH) were considered the most reliable of the indexes tested. The levothyroxine dose may be calculated based on a definite range of thyroid-stimulating hormone levels, but a calculation should also take into account the presence of other associated chronic conditions as well as the cause of the hypothyroidism. Persons suffering from hypothyroidism exhibit an extreme variability in the range of optimal daily levothyroxine doses they require. This wide range makes its very difficult to calculate the average daily dose for a given individual. This underscores the importance of determining the final levothyroxine dose by means of an index rather than by means of calculating an average replacement levothyroxine dose.

Health aspects, Thyroid hormones

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Reappraisal of thyroxine treatment in primary hypothyroidism

Article Abstract:

Thyroid hormone (TH) is essential for normal growth and development in children, and TH deficiencies lead to abnormal physical growth and mental deficiency. However, screening of all newborns and the availability of thyroxine for thyroid hormone replacement has made normal development possible in affected children. The dose of thyroxine, as with any other drug, must be within appropriate limits, as too low a dose would be inadequate, while an excessive dose is associated with adverse side effects. Several ways are available to determine if a dose of thyroxine is biologically appropriate. One is a relatively new test which allows measurement of thyroid stimulating hormone (TSH). TSH is a pituitary hormone which stimulates the thyroid gland to produce TH. Blood levels of TSH increase if TH levels are too low or decrease if TH is too high. The heart is a target of TH action; measurement of heart pumping rhythm is another indicator of TH adequacy. The appropriateness of TH dosages in 13 children (9 female), aged 3 to 16 years was evaluated with these techniques and by measuring blood TH levels. TSH levels were very responsive to decreases in thyroxine dosage. The final thyroxine doses used to maintain TSH levels within the appropriate range were slightly lower than the initial doses taken by the children, and responses were less variable when thyroxine dose was titrated to children's body surface area rather than body weight. One-third of the children reacted to low levels of thyroxine during the study with altered heart rhythm. TSH responses to thyroxine changed more during intervals of increasing thyroxine than during intervals of decreasing thyroxine. This is probably related to the long time needed for the body to eliminate thyroxine. These results suggest that alterations in thyroxine dosages should be made gradually, particularly when dose is reduced. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Low serum thyrotropin (thyroid-stimulating hormone) in older persons without hyperthyroidism

Article Abstract:

Thyrotropin (thyroid stimulating hormone, TSH), a hormone secreted by the pituitary gland, controls the release of thyroid hormone and aids the growth and functioning of the thyroid gland. New, highly sensitive measures of TSH are now available that clearly distinguish between people with normal levels of TSH and those with hyperthyroidism, in whom the concentration is clearly low. There has been very little published about older people with hyperthyroidism, in whom the condition is usually not evident. To remedy this situation, 1,534 women and 1,041 men enrolled in the Framingham Heart Study were examined. All of the subjects were over 60 years old. It was found that many more older people had low levels of TSH than had hyperthyroidism; therefore a low TSH concentration does not confirm a diagnosis of hyperthyroidism in elderly patients, and it may be caused by thyroid hormone treatment. This can be ascertained from the medical history. Although the new assays for measuring serum TSH are the best method for detecting hyperthyroidism, in older people this is not always sufficient. It is recommended that a low serum TSH level be followed by a serum thyroxine (T4) measurement, and observation and repeated testing if necessary. (Consumer Summary produced by Reliance Medical Information, Inc.)

Diagnosis, Measurement, Demographic aspects, Hyperthyroidism

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