BNF for Children 2011-2012

BNFC 2011–2012 6.2.2 Antithyroid drugs 367Hypothyroid coma. By slow intravenous injectionChild 12–18 years 5–20 micrograms repeatedevery 12 hours or up to every 4 hours if necessary;alternatively initially 50 micrograms then 25 microgramsevery 8 hours reducing to 25 microgramstwice dailyLiothyronine sodium (Goldshield) ATablets, scored, liothyronine sodium 20 micrograms,net price 28-tab pack = £26.15Triiodothyronine (Goldshield) AInjection, powder for reconstitution, liothyroninesodium (with dextran). Net price 20-microgram amp= £37.926.2.2 Antithyroid drugsAntithyroid drugs are used for hyperthyroidism either toprepare children for thyroidectomy or for long-termmanagement. In the UK carbimazole is the most commonlyused drug. Propylthiouracil should be reservedfor children who are intolerant of, or who experiencesensitivity reactions to, carbimazole (sensitivity is notnecessarily displayed to both drugs), and for whomother treatments are inappropriate. Both drugs act primarilyby interfering with the synthesis of thyroid hormones.Treatment in children should be undertaken by a specialist.Neutropenia and agranulocytosisDoctors are reminded of the importance of recognisingbone marrow suppression induced by carbimazoleand the need to stop treatment promptly.1. Children and their carers should be asked toreport symptoms and signs suggestive of infection,especially sore throat.2. A white blood cell count should be performed ifthere is any clinical evidence of infection.3. Carbimazole should be stopped promptly ifthere is clinical or laboratory evidence of neutropenia.Carbimazole or propylthiouracil are initially given inlarge doses to block thyroid function. This dose iscontinued until the child becomes euthyroid, usuallyafter 4 to 8 weeks, and is then gradually reduced to amaintenance dose of 30–60% of the initial dose. Alternativelyhigh-dose treatment is continued in combinationwith levothyroxine replacement (blocking-replacementregimen); this is particularly useful when doseadjustment proves difficult. Treatment is usually continuedfor 12 to 24 months. The blocking-replacementregimen is not suitable during pregnancy. Hypothyroidismshould be avoided particularly during pregnancy asit can cause fetal goitre.When substituting, carbimazole 1 mg is consideredequivalent to propylthiouracil 10 mg but the dose mayneed adjusting according to response.Rashes and pruritus are common with carbimazole butthey can be treated with antihistamines without discontinuingtherapy; alternatively propylthiouracil can besubstituted. If a child on carbimazole develops a sorethroat it should be reported immediately because of therare complication of agranulocytosis (see Neutropeniaand Agranulocytosis, above).Iodine has been used as an adjunct to antithyroid drugsfor 10 to 14 days before partial thyroidectomy; however,there is little evidence of a beneficial effect. Iodineshould not be used for long-term treatment becauseits antithyroid action tends to diminish.Radioactive sodium iodide ( 131 I) solution is used increasinglyfor the treatment of thyrotoxicosis at all ages,particularly where medical therapy or compliance is aproblem, in patients with cardiac disease, and in patientswho relapse after thyroidectomy.Propranolol (section 2.4) is useful for rapid relief ofthyrotoxic symptoms and can be used in conjunctionwith antithyroid drugs or as an adjunct to radioactiveiodine. Beta-blockers are also useful in neonatal thyrotoxicosisand in supraventricular arrhythmias due tohyperthyroidism. Propranolol has been used in conjunctionwith iodine to prepare mildly thyrotoxic patients forsurgery but it is preferable to make the patient euthyroidwith carbimazole. Laboratory tests of thyroid functionare not altered by beta-blockers. Most experience intreating thyrotoxicosis has been gained with propranololbut atenolol (section 2.4) is also used.Thyrotoxic crisis (‘thyroid storm’) requires emergencytreatment with intravenous administration of fluids,propranolol and hydrocortisone as sodium succinate,as well as oral iodine solution and carbimazole orpropylthiouracil which may need to be administeredby nasogastric tube.Neonatal hyperthyroidism is treated with carbimazoleor propylthiouracil, usually for 8 to 12 weeks. In severesymptomatic disease iodine may be needed to block thethyroid and propranolol required to treat peripheralsymptoms.Pregnancy Radioactive iodine therapy is contra-indicatedduring pregnancy. Propylthiouracil and carbimazolecan be given but the blocking-replacement regimen(see above) is not suitable. Rarely, carbimazole hasbeen associated with congenital defects, including aplasiacutis of the neonate—use carbimazole in pregnancyonly if propylthiouracil is not suitable. Both propylthiouraciland carbimazole cross the placenta and in highdoses can cause fetal goitre and hypothyroidism—thelowest dose that will control the hyperthyroid stateshould be used (requirements in Graves’ disease tendto fall during pregnancy).Breast-feeding Carbimazole and propylthiouracil arepresent in breast milk but this does not preclude breastfeedingas long as neonatal development is closelymonitored and the lowest effective dose is used.CARBIMAZOLEHepatic impairment use with caution in mild tomoderate impairment; avoid in severe hepaticimpairmentPregnancy see notes above6 Endocrine system