ASK DIS: Management of Hyperthyroidism

Availability:

Tab Carbimazole 5mg

Tab Propylthiouracil 50mg

*Methimazole and Carbimazole are interchangeable (10mg Carbimazole = 6mg Methimazole)

Thionamides:

Thionamide compounds inhibit thyroid hormone synthesis.
They are actively transported into the thyroid gland where they inhibit both the organification of iodine to tyrosine residues in thyroglobulin and the coupling of iodotyrosines

Methimazole (MMI)

MMI is usually preferred over PTU because it reverses hyperthyroidism more quickly and has fewer side effects.
MMI requires an average of six weeks to lower T4 levels to normal and is often given before radioactive iodine treatment.
MMI can be taken once per day.
MMI is less likely than PTU to be associated with failure of radioiodine therapy when thionamides are given to normalize thyroid function before radioiodine treatment

Propylthiouracil (PTU)

PTU does not reverse hyperthyroidism as rapidly as MMI and it has more side effects.
Because of its potential for liver damage, it is used only when MMI or carbimazole are not appropriate.
PTU must be taken two to three times per the day.
indications for PTU:
- In pregnant women during their first trimester
- In patients with life-threatening thyrotoxicosis or thyroid storm (because of PTU's ability to inhibit peripheral conversion of T4 to T3)
- In patients with adverse reactions to MMI (other than agranulocytosis) who are not candidates for radioiodine or surgery

Antithyroid drugs during pregnancy

PTU used to be the drug of choice during pregnancy because it causes less severe birth defects than methimazole.
But experts now recommend that PTU be given during the first trimester only. This is because there have been rare cases of liver damage in people taking PTU.
After the first trimester, women should switch to methimazole for the rest of the pregnancy.
For women who are nursing, methimazole is probably a better choice than PTU (to avoid liver side effects).

Dosing	Carbimazole	PTU
Initial	Mild: 15mg Moderate: 30-40mg Severe: 60mg [in divided doses (TDS)]	initially 300mg/day 400mg/day in severe HyperT occasionally can go up to 600-900mg/day [in 3 divided doses]
Maintenance	5-15 mg OD	100 – 150mg/day
Monitoring	Wide variation in sensitivity Recommended monthly for the first year, thereafter 3-6 monthly interval continued for approximately 12–18 months, then tapered or discontinued if the TSH is normal	Clinical improvement in 1-3 months Dosage reduction maybe needed to prevent HypoT Discontinuation considered after 12-18 months Monitored 2 monthly for 6 months thereafter till remission
Assessment	serum free T4 should be obtained about 4 weeks after initiation and dose adjusted accordingly. Serum T3 also may be monitored, since the estimated serum free T4 levels may normalize with persistent elevation of serum T3. Appropriate monitoring intervals are every 4–8 weeks until euthyroid levels are achieved with the minimal dose Once the patient is euthyroid, biochemical testing and clinical evaluation can be undertaken at intervals of 2–3 months. serum free T4 and TSH are required before treatment and at intervals after starting the treatment. Serum TSH may remain suppressed for several months after starting therapy and is therefore not a good parameter to monitor therapy early in the course

Beta Blockers

beta-blocker should be started (assuming there are no contraindications to its use) in most patients as soon as the diagnosis of hyperthyroidism is made, even before determining the cause of the hyperthyroidism.
Beta-adrenergic blockade should be given to elderly patients with symptomatic thyrotoxicosis and to other thyrotoxic patients with resting heart rates in excess of 90 bpm or coexistent cardiovascular disease.
leads to a decrease in heart rate, systolic blood pressure, muscle weakness, and tremor, as well as improvement in the degree of irritability, emotional lability, and exercise intolerance
They should be continued until resolution of hyperthyroidism.
relative/absolute contraindication - asthma or chronic obstructive pulmonary disease, severe peripheral vascular disease, Raynaud phenomenon, bradycardia, second or third degree heart block, and hypoglycemia-prone diabetics in whom the early warning symptoms of hypoglycemia may be masked
Patients with relative contraindications to beta blockade may better tolerate beta1-selective drugs such as atenolol or metoprolol

References:

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