Dentifrice Reducing Levothyroxine Efficacy in Children

Excerpt

To the Editor: Absorption of thyroxine supplement, used for the treatment of hypothyroidism, is interfered by several drugs and food. A two-years-old girl, a diagnosed case of congenital hypothyroidism (CH) presented to us with elevated thyroid stimulating hormone (TSH) (38 mIU/l). She was started on L-thyroxine (Levothyroxine) at a dose 15 mcg/kg/d elsewhere from day 5 of life after being diagnosed as CH on neonatal screening and was on regular follow-up since then. Previous TSH levels were found be within normal range on multiple occasions as per the medical records and she was taking L-thyroxine 50 mcg/d before visiting us. Growth and developmental milestones were appropriate for her age. She had weight of 12 kg (0 to +1SD) and height of 84 cm (0 to +1 SD) at presentation. Compliance was good. Initially thyroxine dose was increased and compliance was ensured. Despite of hike in dose, repeat TSH after 1 mo remained to be elevated (42 mIU/l). There was no history suggestive of malabsorption syndrome and any other drug intake. On taking detailed history, parents revealed that the child had started brushing her teeth for last few months and she used to swallow the tooth paste while brushing. They used to give thyroxine immediately after brushing in empty stomach. Possibility of toothpaste hampering the absorption of thyroxine was considered. Hence, we advised to change the brushing pattern and introduced reward technique for the child and advised to give the medication in same dose 30–45 min after brushing. TSH level became normal (TSH 3.26 mIU/l) subsequently and we were able to taper down the dose of thyroxine to 37.5 mcg/d on follow-up. …