Thyrox 50mcg

Introduction

Thyrox 50 is a medicine used to treat an underactive thyroid gland (hypothyroidism). It replaces the hormone which was not being produced by your thyroid gland in sufficient quantity and helps regulate your body’s energy and metabolism. Before you start taking Thyrox 50, your doctor will do a blood test to see what dose you need. Once you start taking the medicine, you will have regular blood tests to see how well it is working, and the dose may be adjusted from time to time. Take this medicine exactly as directed by your doctor. It is best taken on an empty stomach before your first meal of the day. You should take this medicine regularly to get the maximum benefit. It may take several weeks before your symptoms start to improve. Keep using this medicine even if you feel well. You may need to take it for the rest of your life. If you stop taking it, your symptoms are likely to come back. The most common side effects of this medicine are caused by taking a bigger dose than you need. Possible side effects include palpitations (irregular heart beat), vomiting, anxiety, diarrhea, weight loss, nervousness or restlessness. Most side effects will disappear once you are on the right dose. Some people may suffer a severe reaction to high levels of thyroid hormone. Call your doctor straight away if you have a very high temperature, fast or irregular heart rate, low blood pressure, yellowness in eye/skin, confusion or fits. Thyrox 50 may cause weight loss but should not be prescribed or taken to treat obesity. If you become pregnant while taking this medicine, inform your doctor right away as the dose may have to be increased/readjusted. Many other drugs affect the way this medicine works. Ask your doctor for advice if you are taking any other medications.

Uses of Thyrox 50

• Hypothyroidism

Side effects of Thyrox 50

• Palpitations
• Vomiting
• Anxiety
• Diarrhea
• Flushing (sense of warmth in the face, ears, neck and trunk)
• Weight loss
• Nervousness
• Restlessness

How to use Thyrox 50

Take this medicine in the dose and duration as advised by your doctor. Swallow it as a whole. Do not chew, crush or break it. Thyrox 50 is to be taken empty stomach.

How Thyrox 50 works

Thyrox 50 is a synthetic version of a hormone produced by the thyroid gland. It works by replacing the thyroid hormones that your thyroid gland cannot produce in a sufficient quantity, and relieves the symptoms of hypothyroidism (tiredness, weight gain, and depression).

What if you forget to take Thyrox 50?

If you miss a dose of Thyrox 50, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular schedule. Do not double the dose.

Indication

Hypothyroidism, TSH suppression, Myxoedema coma

Administration

Should be taken on an empty stomach with full glass of water. Take on an empty stomach ½-1 hr before meals.

Adult Dose

Oral Mild Hypothyroidism 1.7 mcg/kg or 100-125 mcg PO qDay; not to exceed 300 mcg/day >50 years (or <50 yr with CV disease) Usual initial dose: 25-50 mcg/day May adjust dose by 12.5-25 mcg q6-8Week >50 years with CV disease Usual initial dose: 12.5-25 mcg PO qDay May adjust dose by 12.5-25 mcg q4-6weeks until patient becomes euthyroid and serum TSH concentration normalized; adjustments q6-8weeks also used Dose range: 100-125 mcg PO qDay Severe Hypothyroidism Initial: 12.5-25 mcg PO qDay Adjust dose by 25 mcg/day q2-4Week PRN Subclinical Hypothyroidism Initial: 1 mcg/kg PO qDay may be adequate, OR If replacement therapy not initiated, monitor patient annually for clinical status TSH suppression For thyrotropin-dependent well-differentiated thyroid cancer: Doses >2 mcg/kg/day may be given as a single dose to suppress TSH to <0.1 MIU/L. For benign nodules and nontoxic multinodular goitre: Target TSH is generally higher at 0.1-0.5 MIU/L for nodules and 0.5-1 MIU/L for multinodular goitre.

Child Dose

Oral Hypothyroidism Age 1-3 months 10-15 mcg/kg/day PO Use lower starting dose (25 mcg/day) if patient at risk of cardiac failure; if initial serum T4 lower than 5 mcg/dL begin treatment at higher dose (50 mcg/day) Age 3-6 months 8-10 mcg/kg/day PO, OR 25-50 mcg/day PO Age 6-12 months 6-8 mcg/kg/day PO, OR 50-75 mcg/day PO Age 1-5 years 5-6 mcg/kg/day PO, OR 75-100 mcg/day PO Age 6-12 years 4-5 mcg/kg/day PO, OR 100-125 mcg/day PO >12 years 2-3 mcg/kg/day PO, OR 150 mcg/day PO Start children with severe or chronic hypothyroidism at 25 mcg/day; adjust dose by 25 mcg qweek

Contraindication

Untreated hyperthyroidism; uncorrected adrenal failure; recent MI.

Mode of Action

Levothyroxine Na is a synthetic form of thyroxine which increases the basal metabolic rate (BMR) and the utilisation and mobilisation of glycogen stores and stimulates protein synthesis. It is also involved in normal metabolism, growth and development. These effects are mediated at the cellular level by the thyroxine metabolite, tri-iodothyronine.

Precaution

Patients w/ CV (e.g. angina, heart failure, HTN), DM and diabetes insipidus, epilepsy, pre-existing myasthenia syndrome, long-standing hypothyroidism. Elderly, pregnancy and lactation. Monitoring Parameters Monitor thyroid function test, clinical signs of hypo- and hyperthyroidism, heart rate and BP. Lactation: Enters breast milk; use caution

Side Effect

Nervousness, excitability, tremor, muscle weakness, fatigue, cramps; sweating, flushing, heat intolerance, headache, fever, insomnia, tachycardia, palpitations, restlessness, anginal pain, HTN, severe depression, difficulty in sleeping, excessive wt loss; menstrual irregularities; diarrhoea, vomiting, psychosis or agitation. Increased bone resorption and reduced bone mineral density, especially in post-menopausal women; elevated LFT. Potentially Fatal: Thyrotoxic crisis including convulsions, cardiac arrhythmia, heart failure, coma.

Interaction

Reduced absorption w/ iron, antacids, bile acid sequestrants, colestyramine, simeticone, Ca carbonate, sucralfate, cation exchange resins. Reduced tri-iodothyronine serum levels w/ amiodarone and propranolol. Reduced serum levels of thyroxine w/ carbamazepine, phenytoin, phenobarbital, rifampicin, lithium, oestrogens, sertraline. Androgens may decrease levothyroxine-binding globulins serum levels. May alter requirements of antidiabetic drugs. Increased risk of significant HTN and tachycardia w/ ketamine. Increased metabolic demands w/ sympathomimetics (e.g. epinephrine). May increase anticoagulant effect of warfarin.