Brand and Other Names:Northyx, Tapazole
- Classes: Antithyroid Agents
Dosing & Uses
Dosage Forms & Strengths
Mild: 15 mg/day PO divided q8hr initially
Moderate: 30-40 mg/day PO divided q8hr initially
Severe: 60 mg/day PO divided q8hr initially
Maintenance: 5-15 mg/day PO divided q8hr
10-20 mg/day PO; after euthyroidism is achieved, reduce dosage by 50% and administer for 12-18 months
20-30 mg q6-12hr for short term, then reduce dosage to maintenance (5-15 mg/day) or reduce frequency to q12hr or q24hr
Dosage Forms & Strengths
Maintenance: 1/3-2/3 of initial PO dosage divided q8hr PO
Not to exceed 30 mg/day
Serious - Use Alternative
Significant - Monitor Closely
Frequency Not Defined
Dermatologic reactions (eg, rash, pruritus, skin pigmentation)
Salivary gland swelling
Hepatic reactions may occur
Lupuslike syndrome reported
Antineutrophil cytoplasmic autoantibody (ANCA)-positive vasculitis reported
Dosage >40 mg/day
Patient age >40 years
Concurrent administration of other agranulocytosis-causing drugs
Risk of rare but serious agranulocytosis, cholestastic jaundice, and rare congenital abnormalities (propylthiouracil [PTU] preferred in pregnancy)
Prolonged treatment may cause hypothyroidism
Discontinue if agranulocytosis, pancytopenia, hepatitis, fever, or exfoliative dermatitis occurs
10 times more potent than PTU, but action may be less consistent
High rate of relapse (more likely in smokers)
Pregnancy & Lactation
Pregnancy category: D (drug crosses placenta)
Lactation: Drug distributed in breast milk; use contraindicated by manufacturer (American Academy of Pediatrics [AAP] Committee states that drug is compatible with nursing; American Academy of Family Physicians [AAFP] states that it is safe for nursing)
A:Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B:May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C:Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D:Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X:Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA:Information not available.
Mechanism of Action
Inhibits synthesis of thyroid hormone by blocking oxidation of iodine in thyroid gland; blocks synthesis of thyroxine (T4) and triiodothyronine (T3)
Onset: PO, 12-18 hr
Duration: 36-72 hr
Peak plasma time: 1-2 hr
Protein bound: None
Metabolized by liver
Half-life: 4-6 hr
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