Patient Information:
Ref- Advice for the Patient - Drug Information in Lay Language- USPDI (1997)
Antithyroid Drugs include-
Methimazole , Propylthiouracil
1. Replacement therapy is to be taken for life, except in cases of transcient hypothyroidism, usually associated with
thyroditis, and in those receiving a trial of the drug.
2. Take a single daily dose preferably before breakfast
3. Brand interchange- Do not change from one brand of this drug to another without consulting your pharmacist or physician. Products manufactured by different companies may not be equally effective.
4. Do not discontinue medication except on advice of a physician
5. Notify physician if headache, nervousness, diarrhea, excessive sweating heat intolerance, chest pain, increased
pulse rate, palpitations(symptoms of hyperthyroidism) or any usual event occurs
6. Partial loss of hair may be experienced by children in the first few months of therapy, but this usually a
transcient phenomenon that result in later recovery
7. Not for use as primary or adjunctive therapy in a weight control program
8. If levothyroxine is taken on an empty stomach, absorption is increased.
9.Allergies-
Tell your doctor if you have ever had any unusual or allergic reaction to methimazole
or propylthiouracil. Also tell your healthcare provider if you are allergic to any other
substances, such as foods, preservatives or dyes.
10.Pregnancy-
Use of too large a dose during pregnancy may cause problems in the fetus. However,
use of the proper dose , with careful monitoring by the doctor, is not likely to cause
problems
11. Breast-feeding-
These medicines pass into breast milk.(Methimazole passes into breast milk more
freely and in higher amounts than propylthiouracil). However , your doctor may allow
you continue to breast feed . If you are taking a large dose, it may be necessary for
you to stop breast-feeding during treatment
12.Children-
This medicine has not been used in children and in effective doses. has not shown
to cause different side side effects or problems in children than in adults.
13.Teen agers-
The medicine has not been used in teenagers and in effective doses, has not shown
to cause different side effects or problems in teenagers than it does in adults.
14.Older adults-
Elderly people may have an increased chance of certain side effects during
treatment. Your doctor may need to take certain precautions while you are
taking this medicine
15.Other medicines-
Although certain medicines should not be used together at all, in other cases two
different medicines may be used together even interaction might occur. In such
cases your doctor may want to change the dose , or other precautions may be
necessary.
When you are taking antithyroid drugs , it is especially important that
your doctor know if you are taking any of the following-.
Amiodarone or
Iodinated glycerol or
Potassium Iodide (eg.Pima) - the use of these medicines may change the
effect of antithyroid drugs
Anticoagulants(blood thinners) the use of antithyroid drugs may affect the
way the anicoagulants work on your body.
Digitalis glycosides- the use antithyroid agents may affect the amount of
digitalis glycosides in the blood stream
8.Other medical problems-
The presence of other medical problems may affect the use of antithyroid agents.
Make sure you tell your doctor if you have other any other medical problems,
Liver disease- the body may get this medicine out of thre bloodstream at the usual
rate, which may increase the chance of side effects.
Pharmacology/ Pharmacokinetics:
Ref -Drug Facts and comparisons (2010)
Pharmacolgy-
PTU and methimazole inhibit the synthesis of thyroid hormones and thus are effective in
the treatment of hyperthyroidisms. They do not inactivate exiting thyroxineT4 and
triiodothryronine T3 which are stored in the thyroid or which circulate in the blood , nor do they interfere with the effectiveness of exogenous thyroid hormones. PTU partially inhibits the peripheral conversion of T4 to T3
Pharmacokinetics-
Pharmacokinetic data are summarised as-
Various Pharmacokinetic Parameters of Antithyroid agents
Antithyroid Bioavail Protein Trans Breast Milk Half-life Excreted
agent ability binding placental levels (h) in urine
% passage (M:P) (%)
Propylthio 80to 95 75to 80 Low Low)(0.1) 1 to 2 <35
uracil
Methimazole 80to 95 0 High High (0.1) 6 to 13 <10
Manufacturer Details