Question

Assignment chapter 37,Thyroid and parathyroid Agents

Learning Objective(s) Group Assignments 1. As a group, prepare a table describing the therapeutic actions, indications, pharmacokinetics, most common adverse reactions, contraindications, and important drug-drug interactions for thyroid and parathyroid agents. 2. Divide the class into three groups. Assign each group an age group: children, adults, or older adults. Each group is to discuss the use of thyroid and parathyroid agents in the assigned age group. What are the most likely reasons that each age group is receiving one of these drugs? Prepare a presentation describing special considerations for using these agents in the assigned age group. 3. Construct a table that compares and contrasts the prototype drugs levothyroxine, propylthiouracil, strong iodine products, calcitriol, alendronate, and calcitonin with other thyroid or parathyroid agents in their class. Look for similarities and differences among groups.

Answer 1

THYROID AGENTS   :

THYROID HORMONES

Drug Name Usual Indications	Dosage/Route	Usual Indications
Levothyroxine Levoxyl, Levothroid, others)	Adult: 0.05–0.2 mg/d PO, Pediatric: 0.025–0.4 mg/d PO	Replacement therapy in hypothyroidism; suppression -stimulating hormone (TSH) release; treatment of myxedema coma and thyrotoxicosis
Liothyronine (Cytomel, Triostat	Adult: 25–100 mcg/d PO Pediatric: 20–50 mcg/d PO	Replacement therapy in hypothyroidism; suppression of TSH release; treatment of thyrotoxicosis; synthetic hormone used in patients allergic to desiccated thyroid Special considerations: not for use with cardiac or anxiety problems
liotrix (Thyrolar)	Adult: 60–120 mg/d PO Pediatric: 25–150 mcg/d PO based on age and weight	Replacement therapy in hypothyroidism; suppression of TSH release; treatment of thyrotoxicosis Special considerations: not for use with cardiac dysfunction
thyroid desiccated (Armour Thyroid)	Adult: 60–120 mg/d PO Pediatric: 15–90 mg/d PO	Replacement therapy in hypothyroidism; suppression of TSH release; treatment of thyrotoxicosis

. ANTITHYROID AGENTS

Thioamides

Methimazole (Tapazole	Adult: 15 mg/d PO initially, up to 30–60 mg/d may be needed; maintenance, 5–15 mg/d PO	Treatment of hyperthyroidism
Propylthiouracil	Adult: 300–900 mg/d PO initially; maintenance, 100–150 mg/d PO Pediatric: 50–300 mg/d PO based on age and response	Treatment of hyperthyroidism

IODINE SOLUTIONS

sodium iodide I131 (generic, radioactive (generic, radioactive iodine)	Adult (30 yr): 4–10 millicuries PO as Adult (30 yr): 4–10 millicuries PO as needed	Treatment of hyperthyroidism; thyroid blocking in radiation emergencies; destruction of thyroid tissue in patients who are not candidates for surgical removal of the gland
strong iodine solution, potassium iodide (Thyro-Block)	Adult: one tablet, or 2–6 drops (gtt) PO daily to t.i.d Pediatric (1 yr): adult dose Pediatric (1 yr): adult dose daily to t.i.d	Treatment of hyperthyroidism, thyroid blocking in radiation emergencies; presurgical suppression of the thyroid gland, treatment of acute thyrotoxicosis until thioamide levels can take effect

SIDE EFFECTS

Levothyroxine Indications:

Replacement therap y in hypothyroidism; pituitary TSH suppression in the treatment of euthyroid goiters and in the management of thyroid cancer; thyrotoxicosis in conjunction with other therapy; myxedema coma

Adverse effects: Tremors, headache, nervousness, palpitations, tachycardia, allergic skin reactions, loss of hair in the first f w months of therapy in children, diarrhea, nausea, vomiting.

Thionamides

Pharmacokinetics Thioamides These drugs are well absorbed from the GI tract and are then concentrated in the thyroid gland. The onset and duration of PTU varies with each patient. Methimazole has an onset of action of 30 to 40 minutes and peaks in about 60 minutes. Some excretion can be detected in the urine. Methimazole crosses the placenta and is found in a high ratio in breast milk. PTU has a lo w potential for crossing the placenta and for entering breast milk (see Contraindications and Cautions).

Adverse Effects Thioamides The adverse effects most commonly seen with thioamides are the ef fects of thyroid suppression: drowsiness, lethargy, bradycardia, nausea, skin rash, and so on. PTU is associated with nausea, vomiting, and GI complaints. GI effects are somewhat less pronounced with methimazole, so it may be the drug of choice for patients who are unable to tolerate PTU. Methimazole is also associated with bone marrow suppression, so the patient using this drug must have frequent blood tests to monitor for this effect.

IODINE SOLUTIONS

The most common adverse effect of iodine solutions is hypothyroidism; the patient will need to be started on replacement thyroid hormone to maintain homeostasis.

Other adverse effects include iodism (metallic taste and burning in the mouth, sore teeth and gums, diarrhea, cold symptoms, and stomach upset), staining of teeth, skin rash, and the development of goiter. Sodium iodide (radioactive I 131) is usually reserved for use in patients who are older than 30 years of age because of the adverse effects associated with the radioactivity

PARATHYROID AGENTS

Antihypocalcemic agents

Drug Name	Usual Dosage	Usual Indications
calcitriol (Rocaltrol)	0.5–2 mcg/d PO in the morning	Management of hypocalcemia and reduction of parathormone levels
Dihydrotachysterol (Hytakerol)	0.8–2.4 mg/d PO initially, maintenance 0.2–1 mg/d PO based on serum calcium levels	Management of hypocalcemia
teriparatide (Forteo)	20 mg SQ daily	Management of osteoporosis in postmenopausal women and men with primary hypogonada osteoporosis who do not respond to standard therapy

                       Antihypercalcemic agents

Bisphosphonates

Alendronate (Fosamax)	10 mg/d PO; for males and for postmenopausal osteoporosis, 70 mg PO every week or 10 mg/d PO for treatment, 35 mg PO every week or 5 mg/d PO for prevention	Treatment of Paget disease, postmenopausal osteoporosis treatment and prevention, treatment of glucocorticoid-induced osteoporosis, osteoporosis in men
etidronate (Didronel)	5–10 mg/kg per day PO; 7.5 mg/kg per day IV for 3 days for hypercalcemia of malignancy	Treatment of Paget disease, postmenopausal osteoporosis, hypercalcemia of malignancy osteolytic bone lesions in cancer patients
ibandronate (Boniva)	2.5 mg/d PO or 150 mg PO once per month on the same day each month	Treatment of Paget disease; treatment and prevention of osteoporosis in postmenopausal women
pamidronate (Aredia)	60–90 mg IV	Treatment of Paget disease, postmenopausal osteoporosis in women, hypercalcemia of malignancy osteolytic bone lesions in cancer patients
risedronate (Actonel)	30 mg/d PO for 2 mo; reduce dose in renal dysfunction; 5 mg/d PO for osteoporosis	Treatment of symptomatic Paget disease in patients who are at risk for complications; osteoporosis
tiludronate (Skelid)	400 mg/d PO for 3 mo; reduce dose with renal impairment	Treatment of Paget disease that is not responsive to other treatment
zoledronic acid (Zometa)	4 mg IV as a single infusion over not less than 15 min (given once a year for postmenopausal osteoporosis)	Treatment of Paget disease, postmenopausal osteoporosis in women, hypercalcemia of malignancy osteolytic bone lesions in certain cancer patients

CALCITONINS

calcitonin salmon (Miacalcin)	Paget disease: 50–100 International Units/d SQ or IM Postmenopausal osteoporosis: 100 International Units/d SQ or IM with calcium and vitamin D Hypercalcemia: 4–8 International Units/kg SQ or IM q12h	Treatment of Paget disease, postmenopausal osteoporosis in conjunction with vitamin D and calcium supplements; emergency treatment of hypercalcemia
(Fortical)	200 International Units/d intranasally; alternate nostrils daily	Treatment of postmenopausal osteoporosis in conjunction with calcium supplements and vitamin D

Calcitriol Indications:

Management of hypocalcemia in patients on chronic renal dialysis,management of hypocalcemia associated with hypoparathyroidism.

Adverse effects:

Weakness, headache, nausea, vomiting, dry mouth, constipation, muscle pain, bone pain, metallic taste.

Pharmacokinetics Bisphosphonates

These drugs are well absorbed from the small intestine and do not undergo metabolism. They are excreted relatively unchanged in the urine. The onset of action is slo w, and the duration of action is days to weeks. Patients with renal dysfunction may experience toxic le vels of the drug and should be e valuated for a dose reduction. See Contraindications and Cautions for use of these drugs during pregnancy and lactation

CONTRAINDICATIONS

Bisphosphonates

These drugs should not be used in the presence of hypocalcemia, which could be made worse by lowering calcium levels, or with a history of an y allergy to bisphosphonates to avoid hyper sensitivity r eactions. Fetal abnormalities ha ve been associated with these drugs in animal trials, and they should not be used during pregnancy unless the benefit to th mother clearly outweighs the potential risk to the fetus or neonate. Extreme caution should be used when nursing because of the potential for adverse effects on the baby. Alendronate should not be used by nursing mothers. Caution should be used in patients with renal dysfunction, which could interfere with excretion of the drug, or with upper GI disease, which could be aggravated by the drug

ADVERSE EFFECTS

Bisphosphonates

The most common adverse effects seen with bisphosphonates are headache, nausea, and diarrhea. There is also an increase in bone pain in patients with Paget disease, but this effect usually passes after a few days to a few weeks. Esophageal erosion has been associated with alendronate, ibandronate, and risedronate if the patient has not remained upright for at least 30 minutes after taking the tablets