**6.4 Dose calculation**

*Goiter - Causes and Treatment*

**6.1 Adverse events**

**6.3 Radioablation**

this effect is not of much use. The starting dose of MMI is usually 10–30 mg daily in divided doses depending on the severity of hyperthyroidism (CBZ 15–60 mg/ day). PTU is given 100 mg every 8 h. titration regimen is used through the Corse of disease, means as disease goes in remission, dose is gradually reduced based on severity of the illness. Thyroid function tests are reviewed 3–4 weekly intervals after initial treatment, and the dose is titrated based on T4 and T3 levels. TSH values remain suppressed for long time hence more reliable is T3 & T4 reports but measuring T4 does add value to report as sometimes overtreatment increases TSH values in short span. The usual daily maintenance doses of ATD in the titration regimen are 2.5–10 mg of MMI and 50–100 mg of PTU. Some have also advocated block and replacement regimen to avoid severe hypothyroidism during treatment where MMZ in dose of 30–50 mg daily along with thyroxin replacement is used throughout the

Corse but side effects of ATD are more with this kind of regimen [28].

the initiation of ATD was 0.28 and 0.29%, respectively [31].

lems. Hypotension with Propranolol is unusual [32].

**6.2 Beta adrenergic drugs (β blockers)**

Common side effects of ATD are allergic reactions which include rash, urticaria, and arthralgia (1–5%). Minor cutaneous reactions are managed with antihistaminics without stopping the ATD. Substituting an ATD may also be helpful [28]. In the case of a serious allergic reaction like hepatitis, a lupus-like syndrome, and agranulocytosis (neutrophil count <500/mL), which occurs in 0.1–1.0% of cases, it's better to avoid ATD in patients as risk of severity of allergic reaction may increase and it's better to use alternative ways of treatment [29]. Agranulocytosis may occur abruptly within 3 months after the initiation of ATD therapy [30]. The risk of ATD-induced agranulocytosis and pancytopenia at 100 and 150 days after

These drugs are used as second line treatment of adjunctive treatment. These

Introduced in the mid-1940s, a relatively inexpensive therapy for treatment of hyperthyroidism, 131I has become the most widely used therapy, although international questionnaire studies show that geographic differences do exist. The isotope being used is 131I. It is given orally (in a capsule or in water) and is absorbed rapidly and completely, after which it is concentrated, oxidised, and organified by follicular thyroid cells. The ionising effect of β-particles, with a path length of 1–2 mm, destroys the thyroid cells by an early inflammatory response, necrosis of follicular cells, and vascular occlusion. Further chronic inflammation and fibrosis result in a decrease in thyroid size and an impaired thyroid function. So most of

the patients developed Hypothyroidism following 131I therapy [33].

reduce catecholamine response at receptor level hence this is a symptomatic treatment and not a definitive treatment. Tremulousness, palpitations, excessive sweating, eyelid retraction, and heart rate decrease; by reducing sympathetic hyperactivity which is induces by excess TH in blood. Propranolol (but not other β-adrenergic agents) may also weakly block the conversion of T4 to T3 via a mechanism independent of its effect on catecholamine signalling. Propranolol is the most widely used agent because it is relatively free from adverse effects and has a short half-life. It can be given orally in a dose of 20–60 mg every 6 or 8 h and avoided in patients with known history of bronchial asthma or COPD with respiratory prob-

**52**

Smallest possible dose is preferred so that to make patients euthyroid and avoid permanent hypothyroidism in patients. Dose is calculated by following algorithm:

Dose (mCi) = (80 - 200 micro Ci 131I/g thyroid × estimated thyroid gland weight (g) ÷ 24 h radioiodine uptake).

With use of above dose calculation algorithm, usual dose patients receive is 5–15 mCi and many become euthyroid followed by hypothyroidism. Dose calculation is time consuming and costly hence fixed dose activity is commonly used in many centres which simplifies and reduces cost of 131I therapy and the lack of a significant difference in outcome between patients randomised to fixed and calculated 131I doses favour the use of fixed doses. Typically a patient with Graves' disease requires 5–15 mCi, 10–29 mCi in patients with toxic nodule and toxic MNG [33]. Not all patients respond to 131I and these patients may require multiple doses at 6–12 monthly intervals. Patients who can be predicted to have poor response are: (1) age (>40 years); (2) Gender (female); (3) severe hyperthyroidism; (4) medium or large goitres (>40 g, visible); and (5) ATD pre-treatment (especially with propylthiouracil) [34].
