Pharmacologic Therapy PDF

11/7/23, 2:02 PM Realizeit for Student Pharmacologic Therapy Synthetic levothyroxine is the drug of choice for the treatment of hypothyroidism (Drake, 2018). The general range is 75 to 150 mcg per day and treatment is generally started at the lower dose and titrated slowly until desired levels of...

11/7/23, 2:02 PM Realizeit for Student Pharmacologic Therapy Synthetic levothyroxine is the drug of choice for the treatment of hypothyroidism (Drake, 2018). The general range is 75 to 150 mcg per day and treatment is generally started at the lower dose and titrated slowly until desired levels of serum TSH concentration are achieved (Singh & Clutter, 2019). Older adult patients generally require a lower dose; normal TSH levels are often achieved with 50 mcg per day (Singh & Clutter, 2019). Some patients on thyroid hormone replacement may complain of continued clinical manifestations despite normal TSH levels (Chaker et al., 2017). Prevention of Cardiac Dysfunction Any patient who has had hypothyroidism for a long period usually has associated elevated serum cholesterol, atherosclerosis, and coronary artery disease. As long as metabolism is subnormal and the tissues (including the myocardium) require relatively little oxygen, a reduction in blood supply is tolerated without overt symptoms of coronary artery disease. When thyroid hormone is given, the oxygen demand increases, but oxygen delivery cannot be increased unless, or until, the atherosclerosis improves. This occurs very slowly, if at all. The occurrence of angina and acute coronary syndrome is the signal that the oxygen needs of the myocardium exceed its blood supply. Angina or arrhythmias can occur when thyroid replacement is initiated because thyroid hormones enhance the cardiovascular effects of catecholamines. If angina or arrhythmias occur, thyroid hormone administration must be discontinued immediately. Later, when it can be resumed safely, it should be prescribed cautiously at a lower dosage and with close monitoring by the primary provider and the nurse. Prevention of Medication Interactions Oral thyroid hormones interact with many other medications. They increase the effect of warfarin and the cardiovascular effects of adrenergic agents (bronchodilators and vasopressors). In addition, the dosage of insulin and oral hypoglycemic medications used to treat diabetes may require adjustment. Caution is also needed in patients who are concomitantly taking estrogen, which may necessitate an increased dosage of the oral thyroid hormone. Absorption may be affected by any supplement or food that contains calcium, iron, magnesium or zinc (Vallerand & Sanoski, 2018). Even in small IV doses, hypnotic and sedative agents may induce profound somnolence, lasting far longer than anticipated and leading to narcosis (stuporlike condition). Furthermore, they are likely to cause respiratory depression, which can easily be fatal because of decreased respiratory reserve and alveolar hypoventilation. The dose of these medications should be one half or one third of that typically prescribed for patients of similar age and weight with normal thyroid function. Supportive Therapy Severe hypothyroidism and myxedema coma require prompt, aggressive management to maintain vital functions. Arterial blood gases may be measured to determine carbon dioxide retention and to guide the use of assisted ventilation to combat hypoventilation. Oxygen saturation levels should be monitored using pulse oximetry. Fluids are given cautiously because of the danger of water intoxication. Passive rewarming with a blanket is recommended versus active rewarming such as application of external heat (e.g., heating pads). The latter should be avoided to prevent increased oxygen demands and hypotension. Thyroid Drugs Levothyroxine (Synthroid, Levoxyl), a synthetic preparation of thyroxine, serves as the prototype thyroid drug and is considered the standard of care for long-term treatment of hypothyroidism. This potent form of T4 contains a uniform amount of hormone and can be administered orally and parenterally. Pharmacokinetics Absorption of levothyroxine varies after oral administration from 48% to 79%. Taking the drug on an empty stomach increases absorption. In malabsorption syndromes, this results in excessive loss of the drug in the feces. Most (99%) of the circulating drug is bound to serum proteins, including thyroid-binding globulin as well as thyroid-binding prealbumin and albumin. Levothyroxine has a long half-life, about 6 to 7 days in a euthyroid state, but it is prolonged to 9 to 10 days in hypothyroidism and shortened to 3 to 4 days in hyperthyroidism. The drug is metabolized in the liver and excreted in the urine. Action https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=0Dn26kXyU%2f6F5gOCz4%2f2IZMyySaAjt8dTx3FnIrt15HOKniKu5nqplgCFS7%2bEIEJ2a… 1/4 11/7/23, 2:02 PM Realizeit for Student Levothyroxine increases the metabolic rate in the body's tissues, increasing oxygen consumption, respiratory rate, and heart rate. It also increases the metabolism of fats, carbohydrates, and proteins and enhances the growth process. Use Health care providers use levothyroxine as replacement therapy for people with hypothyroidism. Other uses include the following: Treatment and prevention of euthyroid goiters in patients with pituitary suppression of TSH Management of thyroid cancer Prevention of goitrogenesis, hypothyroidism, and thyrotoxicosis during pregnancy (in combination with antithyroid medications) Treatment of myxedema coma It is important to note that the FDA has issued a BLACK BOX WARNING ♦ cautioning prescribers not to order thyroid hormones, either alone or with other therapeutic agents, for the treatment of obesity or for weight loss. Significant and serious complications may develop in euthyroid people who take thyroid hormones. Use in Older Adults Thyroid hormone replacement with levothyroxine increases the workload of the heart and may cause serious adverse effects in older adults, especially those with cardiovascular disease. In such patients, cautious treatment is necessary because of a high risk of adverse effects on the cardiovascular system. Thus, use of smaller initial dosages and smaller drug increments at longer intervals than younger adults is essential. It is important to have periodic measurements of serum TSH levels to monitor drug therapy and to adjust doses when indicated. Also, regular monitoring of blood pressure and pulse is essential. In general, levothyroxine should not be given if the resting heart rate is more than 100 beats/min. Use in Patients With Hepatic Impairment QSEN Alert: Safety Hepatic metabolism of levothyroxine in patients with hypothyroidism is slow, so drug metabolism may be delayed. Many drugs given to these patie important to assess drug reactions in patients with hepatic impairment. Use in Patients With Critical Illness Management of patients in thyroid storm or thyrotoxic crisis is common in the critical care unit. Increased rate of cellular metabolism and oxygen consumption occur with a resultant increase in heat production. The hypermetabolic state increases the metabolism of medications, so increased or more frequent dosing may be necessary. Adverse Effects Adverse effects of levothyroxine include signs and symptoms of hyperthyroidism. Other more serious adverse effects are tachycardia, cardiac dysrhythmias, angina pectoris, myocardial infarction, and heart failure. Nervousness, hyperactivity, insomnia, diarrhea, abdominal cramps, nausea, vomiting, weight loss, fever, and an intolerance to heat have also been reported. Most adverse reactions stem from excessive doses, and signs and symptoms produced are the same as those occurring with hyperthyroidism. Excessive thyroid hormones make the heart work very hard and fast in attempting to meet tissue demands for oxygenated blood and nutrients. Symptoms of myocardial ischemia occur when the increased cardiac workload is prolonged. Cardiovascular problems are more likely to occur in patients who are elderly or who already have heart disease. Contraindications Contraindications to levothyroxine include a known hypersensitivity to active or extraneous constituents of the drug, thyrotoxicosis, and acute myocardial infarction related to hypothyroidism. Caution is warranted in Addison's disease. Affected patients require corticosteroids prior to administration of levothyroxine. Thyroid hormones increase tissue metabolism and tissue demands for adrenocortical hormones. If adrenal insufficiency is not treated first, administration of thyroid hormone may cause acute adrenocortical insufficiency, a life-threatening condition. Also, caution is necessary during lactation and with coronary artery disease or angina. Nursing Implications Preventing Interactions Many medications interact with levothyroxine, increasing and decreasing its effects (Box 42.2 ). https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=0Dn26kXyU%2f6F5gOCz4%2f2IZMyySaAjt8dTx3FnIrt15HOKniKu5nqplgCFS7%2bEIEJ2a… 2/4 11/7/23, 2:02 PM Realizeit for Student Administering the Medication Several factors affect the dosage of levothyroxine: the choice of drug, age and general condition, severity and duration of hypothyroidism, and clinical response to drug therapy. It is essential to individualize the dosage to approximate the amount of thyroid hormone needed to make up the deficit in endogenous hormone production. As a rule, the initial dosage is relatively small, and gradual increases at approximately 2-week intervals are appropriate until symptoms are relieved and a normal serum TSH level (0.5–4.2 microunits/L) is reestablished. Determination of the maintenance dosage for long-term therapy depends on the patient’s clinical status and periodic measurement of serum TSH. People should take levothyroxine in the morning on an empty stomach. If the pulse rate prior to administering the drug is more than 100 beats/min, it is important to notify the prescriber. When giving levothyroxine to an infant or young child, it may be necessary to crush the tablet and add a small amount of formula or water. The child should take the solution with the medication soon after it is mixed; storing the liquid for long periods is a practice to avoid. It is also appropriate to sprinkle the crushed tablet on a small amount of food and then administer it. Assessing for Therapeutic Effects In hypothyroidism, thyroid replacement therapy is lifelong. Medical supervision is necessary frequently during early treatment and at least annually after the patient’s condition has stabilized, and maintenance dosage has been determined. The brand of medication should be consistent; patients should not change brands. The nurse assesses for the following conditions: Increasing energy and diminished sleep Level of alertness and interest in the environment and surroundings Increased pulse rate and blood pressure Bowel regularity and decreased symptoms of constipation Reversal of coarseness of the skin and hair Laboratory values (should decrease as the thyroid hormone is replaced): serum cholesterol, creatinine phosphokinase, lactate dehydrogenase, and aspartate aminotransferase In patients with cretinism, the nurse records the patient’s height periodically to determine an increased in linear growth. In patients with myxedema, the nurse assesses for decreased edema and loss of weight. Assessing for Adverse Effects The nurse assesses for tachycardia and any cardiac dysrhythmias. Excessive thyroid hormones make the heart work very hard and fast in an attempt to meet the tissue demands for oxygenated blood and nutrients. It is necessary to assess for chest pain, edema, and signs of https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=0Dn26kXyU%2f6F5gOCz4%2f2IZMyySaAjt8dTx3FnIrt15HOKniKu5nqplgCFS7%2bEIEJ2a… 3/4 11/7/23, 2:02 PM Realizeit for Student heart failure. Symptoms of myocardial infarction occur when the myocardium does not have an adequate supply of oxygenated blood. Symptoms of heart failure occur when the increased cardiac workload is prolonged. Patient Teaching Box 42.3 provides patient teaching guidelines for levothyroxine. BOX 42.3 Patient Teaching Guidelines for Levothyroxine Thyroid hormone is required for normal body functioning and for life. When your thyroid gland is unable to produce enough thyroid hormone, levo substitute. Thus, levothyroxine therapy for hypothyroidism is lifelong; stopping it may lead to a life-threatening illness. Have periodic tests of thyroid function. Understand that dosage adjustments may occur according to clinical response and results of thyroid function tests. Do not switch from one drug brand to another; effects may be different. Consult a health care provider before taking over-the-counter drugs that stimulate the heart or cause nervousness (e.g., asthma remedies, cold r stimulates the central nervous system and the heart; excessive stimulation may occur if it is taken with other stimulating drugs. In addition, you s caffeine-containing beverages to two to three servings daily. Take the drug every morning, on an empty stomach, for best absorption. Also, do not take the drug with an antacid (e.g., Tums, Maalox), an iron These drugs decrease absorption of levothyroxine. If it is necessary to take one of these drugs, take levothyroxine 2 hours before or 4 to 6 hours Take the drug at about the same time each day for more consistent blood levels and more normal body metabolism. Report chest pain, heart palpitations, nervousness, or insomnia to the prescriber. These adverse effects result from excessive stimulation and ma other stimulants needs to be reduced. https://herzing.realizeithome.com/RealizeitApp/Student.aspx?Token=0Dn26kXyU%2f6F5gOCz4%2f2IZMyySaAjt8dTx3FnIrt15HOKniKu5nqplgCFS7%2bEIEJ2a… 4/4