Tapazole
Tapazole
[tap´ah-zōl]methimazole
Pharmacologic class: Thiomidazole derivative
Therapeutic class: Antithyroid drug
Pregnancy risk category D
Action
Directly interferes with thyroid synthesis by preventing iodine from combining with thyroglobulin, leading to decreased thyroid hormone levels
Availability
Tablets: 5 mg, 10 mg
Indications and dosages
➣ Mild hyperthyroidism
Adults and adolescents: Initially, 15 mg P.O. daily in three equally divided doses at approximately 8-hour intervals. For maintenance, 5 to 15 mg/day in equally divided doses at approximately 8-hour intervals.
Children: Initially, 0.4 mg/kg/day in three divided doses at 8-hour intervals. For maintenance, approximately 0.2 mg/kg/day in three divided doses at 8-hour intervals.
➣ Moderate hyperthyroidism
Adults and adolescents: Initially, 30 to 40 mg P.O. daily in three equally divided doses at approximately 8-hour intervals. For maintenance, 5 to 15 mg/day in three equally divided doses at approximately 8-hour intervals.
Children: 0.4 mg/kg/day P.O. as a single dose or in divided doses at 8-hour intervals. For maintenance, approximately 0.2 mg/kg/day as a single dose or in three divided doses at 8-hour intervals.
➣ Severe hyperthyroidism
Adults and adolescents: Initially, 60 mg/day P.O. in three equally divided doses at approximately 8-hour intervals. For maintenance, 5 to 15 mg/day in three equally divided doses at approximately 8-hour intervals.
Children: Initially, 0.4 mg/kg/day P.O. as a single dose or in three divided doses at 8-hour intervals. For maintenance, approximately 0.2 mg/kg/day as a single dose or in three divided doses at 8-hour intervals.
Contraindications
• Hypersensitivity to drug
• Breastfeeding
Precautions
Use cautiously in:
• bone marrow depression
• patients older than age 40
• pregnant patients.
Administration
• Give with meals as needed to reduce GI upset.
Adverse reactions
CNS: headache, vertigo, paresthesia, neuritis, depression, neuropathy, CNS stimulation
GI: nausea, vomiting, constipation, epigastric distress, ileus, salivary gland enlargement, dry mouth, anorexia
GU: nephritis
Hematologic: thrombocytopenia, agranulocytosis, leukopenia, aplastic anemia
Hepatic: jaundice, hepatic dysfunction, hepatitis
Metabolic: hypothyroidism
Musculoskeletal: joint pain, myalgia
Skin: rash, urticaria, skin discoloration, pruritus, erythema nodosum, exfoliative dermatitis, abnormal hair loss
Other: fever, lymphadenopathy, lupuslike syndrome
Interactions
Drug-drug. Aminophylline, oxtriphylline, theophylline: decreased clearance of both drugs
Amiodarone, iodine, potassium iodide: decreased response to methimazole
Anticoagulants: altered requirements for both drugs
Beta-adrenergic blockers: altered beta blocker clearance
Digoxin: increased digoxin blood level
Drug-diagnostic tests. Granulocytes, hemoglobin, platelets, white blood cells: decreased values
Patient monitoring
• Check for agranulocytosis in patients older than age 40 and in those receiving more than 40 mg/day.
• Assess hematologic studies. Agranulocytosis usually occurs within first 2 months of therapy and is rare after 4 months.
• Monitor thyroid function tests periodically. Once hyperthyroidism is controlled, elevated thyroid-stimulating factor indicates need for dosage decrease.
• Assess liver function tests and check for signs and symptoms of hepatic dysfunction.
• Monitor patient for fever, sore throat, and other evidence of infection as well as for unusual bleeding or bruising.
• Assess patient for signs and symptoms of hypothyroidism, such as hard edema of subcutaneous tissue, drowsiness, slow mentation, dryness or loss of hair, decreased temperature, hoarseness, and muscle weakness.
Patient teaching
• Tell patient to take with meals if GI upset occurs.
• Advise patient to take exactly as prescribed to maintain constant blood level.
• Tell patient to report rash, fever, sore throat, unusual bleeding or bruising, headache, rash, yellowing of skin or eyes, abdominal pain, vomiting, or flulike symptoms.
• Caution female patient not to breastfeed while taking drug.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.
methimazole
(meth-im-a-zole) methimazole,Tapazole
(trade name)Classification
Therapeutic: antithyroid agentsIndications
Action
Therapeutic effects
Pharmacokinetics
Time/action profile (effect on thyroid function)
| ROUTE | ONSET | PEAK | DURATION |
|---|---|---|---|
| PO | 1 wk | 4–10 wk | wk |
Contraindications/Precautions
Adverse Reactions/Side Effects
Central nervous system
- drowsiness
- headache
- vertigo
Gastrointestinal
- diarrhea
- hepatotoxicity
- loss of taste
- nausea
- parotitis
- vomiting
Dermatologic
- rash (most frequent)
- skin discoloration
- urticaria
Hematologic
- agranulocytosis (life-threatening)
- anemia
- leukopenia
- thrombocytopenia
Musculoskeletal
- arthralgia
Miscellaneous
- fever
- lymphadenopathy
Interactions
Drug-Drug interaction
Additive bone marrow depression with antineoplastics or radiation therapy.Antithyroid effect may be ↓ by potassium iodide or amiodarone.↑ risk of agranulocytosis with phenothiazines.May alter response to warfarin and digoxin.Route/Dosage
Availability (generic available)
Nursing implications
Nursing assessment
- Monitor response for symptoms of hyperthyroidism or thyrotoxicosis (tachycardia, palpitations, nervousness, insomnia, fever, diaphoresis, heat intolerance, tremors, weight loss, diarrhea).
- Assess for development of hypothyroidism (intolerance to cold, constipation, dry skin, headache, listlessness, tiredness, or weakness). Dose adjustment may be required.
- Assess for skin rash or swelling of cervical lymph nodes. Treatment may be discontinued if this occurs.
- Lab Test Considerations: Monitor thyroid function studies prior to therapy, monthly during initial therapy, and every 2–3 mo during therapy.
- Monitor WBC and differential counts periodically during therapy. Agranulocytosis may develop rapidly; usually occurs during the first 2 mo and is more common in patients over 40 yr and those receiving >40 mg/day. This necessitates discontinuation of therapy.
- May cause ↑ AST, ALT, LDH, alkaline phosphatase, serum bilirubin, and prothrombin time.
Potential Nursing Diagnoses
Noncompliance (Patient/Family Teaching)Implementation
- Do not confuse methimazole with metolazone.
- Oral: Administer at same time in relation to meals every day. Food may either increase or decrease absorption.
Patient/Family Teaching
- Instruct patient to take medication as directed, around the clock. Take missed doses as soon as remembered; take both doses together if almost time for next dose; check with health care professional if more than 1 dose is missed. Consult health care professional prior to discontinuing medication.
- Instruct patient to monitor weight 2–3 times weekly. Notify health care professional of significant changes.
- May cause drowsiness. Caution patient to avoid driving or other activities requiring alertness until response to medication is known.
- Advise patient to consult health care professional regarding dietary sources of iodine (iodized salt, shellfish).
- Advise patient to report sore throat, fever, chills, headache, malaise, weakness, yellowing of eyes or skin, unusual bleeding or bruising, rash, or symptoms of hyperthyroidism or hypothyroidism promptly.
- Instruct patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult with health care professional before taking other medications.
- Advise patient to carry identification describing medication regimen at all times.
- Advise patient to notify health care professional of medication regimen prior to treatment or surgery.
- Emphasize the importance of routine exams to monitor progress and to check for side effects.
Evaluation/Desired Outcomes
- Decrease in severity of symptoms of hyperthyroidism (lowered pulse rate and weight gain).
- Return of thyroid function studies to normal.
- May be used as short-term adjunctive therapy to prepare patient for thyroidectomy or radiation therapy or may be used in treatment of hyperthyroidism. Treatment from 6 mo to several yr may be necessary, usually averaging 1 yr.