Thyroxine levothyroxine

Thyroxine (levothyroxine) is indicated in hypothyroidism as a maintenance therapy on a long-term basis. The initial dose must not exceed 100 pg. The usual maintenance dose is 100-200 pg. The dose is decreased in elderly patients. Thyroxine must be taken in the morning. 

Loss of efficacy relates to the pharmacokinetic properties of the drugs. With some short t/f drugs there is a simple issue of a transient drop in plasma concentration below a defined therapeutic level. But with others there may be complex issues such as recovery of negative feedback homoeostatic mechanisms, e.g. adrenocortical steroids. Therajjeutic effect may not decline in parallel with plasma concentration. With some drugs a single missed dose may be important, e.g. oral contraceptives, with others (long tj ) several doses may be omitted before there is any serious decline in efficacy, e.g. thyroxine (levothyroxine). 

Levothroid thyroxine, levothyroxine sodium thyroxine, levoxadrol dloxadrol. levoxadrol hydrochloride dioxadrol. 

Despite the availability of a wide array of thyroid hormone products, it is clear that synthetic levothyroxine (LT4) is the treatment of choice for almost all patients with hypothyroidism. LT4 mimics the normal physiology of the thyroid gland, which secretes mostly T4 as a prohormone. As needed, based on metabolic demands, peripheral tissues convert thyroxine (T4)... 

Levothyroxine (L-thyroxine, T4) is the drug of choice for thyroid hormone replacement and suppressive therapy because it is chemically stable, relatively inexpensive, free of antigenicity, and has uniform potency however, any of the commercially available thyroid preparations can be used. Once a particular product is selected, therapeutic interchange is discouraged. 

Levothyroxine (also marketed as Levoxyl, Levothroid, Synthroid, or L-thyroxine sodium) is the only thyroid system prescription that has recently featured prominently among the top 200 medications in the United States. Thus, 75.1 million, 80.7 million, and 79.4 million levothyroxine prescriptions were dispensed in 2003, 2004, and 2005, respectively. At these rates, levothyroxine by itself comprised 3.5, 2.9, and 3.4% of the total prescriptions in the top 200 most popular drugs in the United States in 2003, 2004, and 2005, respectively, making it the most prescribed drug. Levothyroxine is a synthetic version of the natural hormone thyroxine, which is released by the thyroid gland. The natural hormone is important in the development of fetuses and newborns, playing a role in cmcial processes such as the development... 

Hypothyroidism can occasionally be treated with a regular intake of iodide, but in the case of non-functioning of the gland thyroxine must be used. Synthetic levothyroxine... 

Lithium Plus Thyroid Supplementation. Treatment-resistant and rapid-cycling bipolar patients may have an increased frequency of thyroid dysfunction. Further, some patients suffer from subclinical hypothyroidism and improve with the addition of thyroid supplementation. In this context, several case reports involving this population found that high doses of the thyroid hormone levothyroxine sodium (T ) were clinically beneficial (122,123 and 124). Kusalic (1.25) found that 6 of 10 rapid cyclers had hypothyroidism, based on their thyrotropin-releasing hormone stimulation tests. Further, the average number of mood episodes per year decreased by more than 75% (i.e., from 9.7 to 2.2) after thyroxine was added to the treatment regimen. 

The only effective treatment is replacement therapy with thyroid hormones. Levothyroxine, a synthetic levoisomer of thyroxine (T4), is the drug of choice since it is stable, relatively inexpensive, free of antigenicity, and of uniform potency. It results in a pool of thyroid hormone that is rapidly converted into the more potent T3. Levothyroxine can be administered orally or... 

It is best used for short-term suppression of TSH. Because oral administration of T3 is unnecessary, use of the more expensive mixture of thyroxine and liothyronine (liotrix) instead of levothyroxine is never required. 

As with all forms of long-term therapy, adherence to the prescribed dosage of levothyroxine is not always optimal, and an unwarranted fear of thyroid-induced osteoporosis can add to this lack of adherence. Inadequacy of thyroxine replacement therapy is not always easily recognized. Several patients were reported with clearly inadequate or excessive consumption of levothyroxine despite a correct prescription. All patients had depression, which could be an additional susceptibility factor by promoting lack of adherence, and the resulting hypothyroidism or hyperthyroidism could further aggravate the depression (12). 

When replacement therapy is with levothyroxine only, the T4/T3 ratio is increased compared with healthy subjects, suggesting that thyroid secretion of T3 is physiologically important. Animal studies have shown that euthyroidism is not restored in all tissues by levothyroxine alone (13). Mood and neuropsychological function improved in hypothyroid patients when 50 micrograms of thyroxine was replaced by 12.5 micrograms of liothyr-onine (14). 

Several studies have failed to confirm the benefits of combined levothyroxine and liothyroninc therapy. Liothyroninc given once a day results in non-physiologi-cal peak serum concentrations of T3. Modified-release triiodothyronine plus thyroxine can normalize serum biochemistry, but it is not known whether this formulation is superior to levothyroxine alone (15). 

Although liothyronine is three to four times more potent than levothyroxine, it is not recommended for routine replacement therapy because of its shorter half-life (24 hours), which requires multiple daily doses its higher cost and the greater difficulty of monitoring its adequacy of replacement by conventional laboratory tests. Furthermore, because of its greater hormone activity and consequent greater risk of cardiotoxicity, T3 should be avoided in patients with cardiac disease. It is best used for short-term suppression of TSH. Because oral administration of T3 is unnecessary, use of the more expensive mixture of thyroxine and liothyronine (liotrix) instead of levothyroxine is never required. 

However, a contaminated mass spectrometer may cause various response trends toward different compounds. For example, after a triple quadrupole MS was contaminated with ascorbic acid, different response patterns were observed for levothyroxine (ANA), liothy-ronine (ANB), and their internal standard (thyroxine-13C6) during the repetitive injections of pure reference solutions containing these three components (Fig. 11). The responses of ANA were relatively stable while those of ANB and IS decreased significantly over a time period of about 1 and half hours, which resulted in increasing analyte/IS response ratios for levothyroxine and decreasing ratios for liothyronine. 

Fig. 11 An ascorbic acid-contaminated triple quadrupole mass spectrometer affected the responses of levothyroxine (ANA), liothyronine (ANB), and 13C6-thyroxine (IS) differently when a neat solution sample was repeatedly injected, resulting in a gradual increase of analyte/IS response ratios for one analyte (ANA) while gradual decrease for the other (ANB)...

Hypothyroidism is treated with levothyroxine (T4). The drug is given once daily because of its long half-life. Steady state is achieved at 6-8 weeks. Toxicity is directly related to thyroxine levels and manifests itself as nervousness, heart palpitations and tachycardia, intolerance to heat and unexplained weight loss. 

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