1 Dosing Considerations • TAPAZOLE treatment can cause hypothyroidism and adjustments in dosing are necessary to maintain a euthyroid state (see 7 WARNINGS AND PRECAUTIONS, Endocrine and Metabolism, Hypothyroidism). Excess dosage should be avoided as it can lead to sub-clinical or clinical hypothyroidism and goitre growth (see7 WARNINGS AND PRECAUTIONS, Respiratory).
Periodic monitoring of thyroid function should be performed with dosage adjustments as necessary and with more careful monitoring in patients with large goitres (see 7 WARNINGS AND PRECAUTIONS, Monitoring and Laboratory Tests). 4 Drug-Drug Interactions).
• TAPAZOLE can only be administered during pregnancy after a strict individual benefit/risk assessment and only at the lowest effective dose, without additional administration of thyroid hormones. 1 Pregnant Women). 2 Recommended Dose and Dosage Adjustment Adult (≥18 years of age): The initial daily dose is 15 mg for mild hyperthyroidism, 30 to 40 mg for moderately severe hyperthyroidism, and 60 mg for severe hyperthyroidism, divided into three doses at eight-hour intervals.
The maintenance dosage is 5 to 15 mg daily.
Geriatric (≥65 years of age):
Clinical studies of methimazole did not include sufficient numbers of subjects aged 65 or over to determine whether they respond differently from younger subjects. In general, dose selection for an elderly patient should be cautious reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.
3 Pediatrics).
Hepatic impairment:
The dose should be kept as low as possible, and patients should be closely monitored as the plasma clearance of methimazole is reduced (see 7 WARNINGS AND PRECAUTIONS, Monitoring and Laboratory Tests).
Renal impairment:
The dose should be kept as low as possible and careful individual dose adjustment under close monitoring is recommended as there is a lack of data regarding the pharmacokinetic behaviour of methimazole in patients with renal impairment.
4 Administration • TAPAZOLE is administered orally. • TAPAZOLE is usually given in three equal doses per day at approximately eight-hour intervals. 5 Missed Dose If a dose is missed, patients should contact their healthcare professional.
Patients should not take a double dose to make up for a forgotten dose. Patients should take their next scheduled dose as usual. 5 OVERDOSAGE Symptoms: Symptoms may include nausea, vomiting, epigastric distress, headache, fever, joint pain, pruritus, and edema.
Aplastic anemia (pancytopenia) or agranulocytosis may be manifested in hours to days. Less frequent events are hepatitis, nephrotic syndrome, exfoliative dermatitis, neuropathies, and CNS stimulation or depression. Although not well studied, methimazole-induced agranulocytosis is generally associated with doses of 40 mg or more in patients older than 40 years of age.
Overdose may also lead to hypothyroidism with corresponding symptoms of a reduced metabolism and, through the feedback effect, to activation of the adenohypophysis with subsequent goitre growth. This can be avoided by dose reduction as soon as a euthyroid metabolic condition is achieved.
No information is available on the median lethal dose (LD50) of the drug or the concentration of methimazole in biologic fluids associated with toxicity and/or death.
TAPAZOLE® (methimazole tablets) Product Monograph Page 6 of 17 Treatment:
In managing overdosage, consider the possibility of multiple drug overdoses, interaction among drugs, and unusual drug kinetics in your patient. The patient’s bone marrow function should be monitored. In case of suspected overdose, patients should be closely monitored for signs or symptoms of adverse reactions and appropriate symptomatic treatment should be instituted as required.
Forced diuresis, peritoneal dialysis, hemodialysis or charcoal hemoperfusion have not been established as beneficial for an overdose of methimazole. 6 DOSAGE FORMS, STRENGTHS, COMPOSITION AND PACKAGING Table 1 – Dosage Forms, Strengths, Composition and Packaging 5 mg tablets: Each round, white, scored tablet is debossed with ‘J94’ on one side and plain on the other side.
10 mg tablets: Each round, white tablet is debossed with ‘10’ on one side and plain on the other side. TAPAZOLE tablets are supplied in bottles of 100. 7 WARNINGS AND PRECAUTIONS Please see 3 SERIOUS WARNINGS AND PRECAUTIONS BOX. General Patients who receive methimazole should be under close surveillance.
Physicians should encourage patients to immediately report any evidence of illness or unusual clinical symptoms, particularly sore throat, skin eruptions, fever, headache, or general malaise. In such cases, white blood cell and differential counts should be made to determine whether agranulocytosis has developed.
Particular care should be exercised with patients who are receiving additional drugs known to cause agranulocytosis. The development of arthralgias should prompt drug discontinuation, since this symptom may indicate a severe transient migratory polyarthritis known as “the antithyroid arthritis syndrome”.
Carcinogenesis and Mutagenesis Animal data has shown thyroid hyperplasia, thyroid adenoma, and carcinoma formation (see 16 NON- CLINICAL TOXICOLOGY, carcinogenicity). For management of a suspected drug overdose, contact your […]