Synthroid (levothyroxine)

Clinical Medications Worksheets Generic Name levothyroxine

Trade Name Synthroid

Peak 1-3 wk

Onset unknown

Classification Thyroid preparations Duration 1-3 wk

Why is your patient getting this medication Replacement/substitution in diminished or absent thyroid function. Mechanism of action and indications (Why med ordered) Levothyroxine acts like the endogenous thyroid hormone thyroxine (T4, a tetra-iodinated tyrosine derivative). In the liver and kidney, T4 is converted to T3, the active metabolite. In order to increase solubility, the thyroid hormones attach to thyroid hormone binding proteins, thyroxin-binding globulin, and thyroxin-binding prealbumin (transthyretin). Transport and binding to thyroid hormone receptors in the cytoplasm and nucleus then takes place. Thus by acting as a replacement for natural thyroxine, symptoms of thyroxine deficiency are relieved.

Interactions with other patient drugs, OTC or herbal medicines (ask patient specifically) Lanoxin: The clearance of or sensitivity to digitalis glycosides may be increased in previously hypothyroid patients when a euthyroid state is achieved after the addition of thyroid hormones. Lantus, NovoLog: The efficacy of oral hypoglycemic agents and insulin may be diminished by certain drugs, including thiazides and other diuretics, corticosteroids, estrogens, progestins, thyroid hormones, human growth hormone, phenothiazines, atypical antipsychotics, sympathomimetic amines, protease inhibitors, phenytoin, clozapine, megestrol, danazol, isoniazid, asparaginase, pegaspargase, diazoxide, temsirolimus, as well as pharmacologic dosages of nicotinic acid and adrenocorticotropic agents. These drugs may interfere with blood glucose control because they can cause hyperglycemia, glucose intolerance, new-onset diabetes mellitus, and/or exacerbation of preexisting diabetes. Food interactions: Consumption of certain foods as well as the timing of meals relative to dosing may affect the absorption of T4 thyroid hormone (i.e., levothyroxine). T4 absorption is increased by fasting and decreased by foods such as soybean flour (e.g., infant formula), cotton seed meal, walnuts, dietary fiber, calcium, and calcium fortified juices.

Synthroid (levothyroxine)

Dose 125 mcg

Route PO

Time/frequency qd

Normal dosage range Hypothyroidism--50 mcg as a single dose initially; may be increased q 2-3 wk; usual maintenance dose is 75-125 mcg/day (1.5 mcg/kg/day). Severe hypothyroidism--12.5-25 mcg/day; may increase q 2-4 wk by 25 mcg/day; usual maintenance dose is 75-125 mcg/day (1.5 mcg/kg/day). Geriatric Patients and Patients with Increased Sensitivity to Thyroid Hormones: 12.5-25 mcg as a single dose initially; may be increased q 6-8 wk; usual maintenance dose is 75 mcg/day. For IV meds, compatibility with IV drips and/or solutions N/A Nursing Implications (what to focus on) Contraindications/warnings/interactions Hypersensitivity, recent MI, thyrotoxicosis. Cardiovascular disease (initiate therapy with lower doses), secere renal insufficiency, uncorrected adrenocortical disorders, swallowing difficulty. Desiccated thyroid preparations (Armour thyroid, Thyrar) appear on Beers list due to concerns about cardiac effects. Also, Geriatric patients areextremely sensitive to thyroid hormones in general and initial dosage should be markedly reduced. Myxedematous patients (extremely sensitive to thyroid hormones--initial dosage should be markedly reduced). Common side effects Insomnia, irritability, nervousness, CARIOVASCULAR COLLAPSE, arrhythmias, tachycardia, weight loss Lab value alterations caused by medicine Monitor thyroid function studies prior to and during therapy. Monitor blood and urine glucose in diabetic patients. Insulin or oral hypoglycemic dose may need to be increased. Be sure to teach the patient the following about this medication Instruct patient to take medication as directed at the same time each day. Take missed doses as soon as remembered unless almost time for next dose. If more than 2-3 doses are missed, notify health care professional. Do not discontinue without consulting health care professional. Instruct patient and family on correct technique for checking pulse. Dose should be withheld and health care professional notified if resting pulse >100 bpm. Explain to patient that medication does not cure hypothyroidism; it provides a thyroid hormone. Therapy is lifelong. Caution patient not to change brands of thyroid preparations, as this may affect drug bioavailability. Advise patient to notify health care professional if headache, nervousness, diarrhea, excessive sweating, heat intolerance, chest pain, increased pulse rate, palpitations, weight loss >2 lb/wk, or any unusual symptoms occur. Caution patient to avoid taking other medications concurrently with thyroid preparations unless instructed by health care professional. Instruct patient to inform health care professional of thyroid therapy. Emphasize importance of follow-up exams to monitor effectiveness of therapy. Thyroid function tests are performed at least yearly.

Nursing Process- Assessment (Pre-administration assessment) Assess apical pulse and blood pressure prior to and periodically during therapy. Assess for tachyarrhythmias and chest pain.

Synthroid (levothyroxine)

Assessment Why would you hold or not give this med? Overdose is manifested as hyperthyroidism (tachycardia, chest pain, nervousness, insomnia, diaphoresis, tremors, weight loss). Usual treatment is to withhold dose for 2-6 days. Acute overdose is treated by induction of emesis or gastric lavage, followed by activated charcoal. Sympathetic overstimulation may be controlled by antiadrenergic drugs (beta blockers), such as propranolol. Oxygen and supportive measures to control symptoms such as fever are also used. Hypersensitivity. Cardiac complications. Resting pulse >100.

Evaluation Check after giving Lab values approaching normal (TSH: 0.4-4.5 U/ml, T3 Total: 60181 ng/mL, T4 Total: 5.5-12.3 ng/mL), free from hypothyroid symptoms