Carbimazole, in 3 divided daily doses, is commonly prescribed for the treatment of thyrotoxicosis. However, based on its long intra-thyroid half-life, the drug may be effective when used as a single or twice daily dose. This study was undertaken to determine the effect of once, twice or thrice daily doses of carbimazole on thyroid function in patients with thyrotoxicosis. Seventy previously untreated thyrotoxic patients were randomly allocated to receive carbimazole 30 mg once (group 1), 15 mg twice (group 2) and 10 mg thrice (group 3) daily. All patients were also prescribed propranolol 20 mg thrice daily for the first 4 weeks. Blood was taken for total T3, T4, TSH, blood counts and liver enzymes determinations at the beginning and at 6 weeks of treatment. Only 48 (68.6%) patients were included in the analysis, as the rest defaulted follow-up (20.0%) or blood samples were not available at review (11.4%). Of the 48 patients, 17 were in group 1, 16 in group 2 and 15 in group 3. Following 6 weeks of treatment, there was no significant difference in the mean serum levels of total T3 and T4 between the 3 groups. However, there was a significant decrease in the mean serum levels of total T3 and T4 as compared to the start of the treatment. Four patients (23.5%) in group 1, 4 patients (25%) in group 2 and 3 patients (20%) in group 3 were still thyrotoxic at 6 weeks of treatment, whilst 10 patients (58.8%) in group 1, 6 patients (37.5%) in group 2 and 3 (20%) in group 3 were biochemically hypothyroid.(ABSTRACT TRUNCATED AT 250 WORDS)
Twenty eight patients with hyperthyroidism complicating their pregnancies were seen at the Obstetrics and Gynaecology Department, University Hospital, Kuala Lumpur, Malaysia in a six-year period. All patients were treated with antithyroid drugs, carbimazole being the mainstay of treatment. The incidence of the disease was 0.9 per 1000 births and was similar with other series. No cases of fetal goitre were noted. The mean birth weight was 2952 g; there was no significant difference in the birth weight of term live births in patients treated with carbimazole alone or carbimazole combined with propranolol.
The authors describe a case of a 37-year-old Malay lady with an unusually slow carbamazepine clearance, which may be related to genetic polymorphisms of drug metabolizing enzymes and transporters. When given a small daily dose of 200 mg immediate-release carbamazepine, this patient experienced drowsiness. Subsequently, she reduced her carbamazepine dose to 200 mg twice a week (on Mondays and Fridays), resulting in poor seizure control. At the same time, the patient was diagnosed with hyperthyroidism and was given carbimazole and propranolol. Hyperthyroidism and the concurrent use of these antihyperthyroid agents may have further slowed down the metabolism of carbamazepine. Therapeutic drug monitoring of carbamazepine was carried out, and a slow carbamazepine clearance of 1.45 L·h⁻¹ per 70 kg was observed. Genotyping of selected genetic variants in CYP3A4, CYP3A5, EPHX1, ABCB1, and ABCC2 revealed that she has CYP3A5*3/*3 and ABCB1 3435-CC genotypes. Both genotypes have been shown to be associated with higher adjusted mean serum carbamazepine concentration in Chinese and Korean patients with epilepsy. Physicians should be vigilant about the risk of adverse effects among patients with a slow carbamazepine clearance, especially in Malays. Simulations of carbamazepine dosing regimen based on the pharmacokinetic parameters of this patient were performed to allow individualization of drug therapy.