Pregnancy and breastfeeding are times of increased dietary calcium requirement. Dairy foods are an important source of calcium and other nutrients. We became aware that some pregnant women taking thyroxine were being advised by pharmacy prescribing software to avoid dairy products for 2 hours after thyroxine administration, out of keeping with current evidence.
We surveyed 38 consecutive women who attended the Alfred Health Endocrinology in Pregnancy Clinic and were taking thyroxine, to determine their dairy intake and whether they had received advice to avoid dairy for specific time periods after their thyroxine dose.
Thirty-one participants were pregnant and 7 postpartum, 6 of whom were breastfeeding. Median duration of thyroxine use was 7.8 months (range 0.1-10.2 years). Only 13 of 35 women (37%) met the recommended 2½ serves of dairy/day(1). One woman met the higher recommendation of 4 serves/day(2). Thirteen participants (34%) reported being instructed to avoid dairy with thyroxine; 8 of which had been given a time frame (1-2 hours).
We found that in 2019 the Australian Pharmaceutical Formulary (APF) Handbook(3) recommended dispensing of thyroxine with a label stating ‘Do not take dairy products, antacids or mineral supplements within two hours of each dose of this medicine’ despite the lack of evidence for this recommendation. We wrote to the medical dispensing software companies and the APF New Drugs Advisory Group to advise of this inaccuracy. This resulted in the APF amending their recommendation to remove mention of dairy products from this label(4).
Hypothyroidism requiring thyroxine replacement is common in pregnancy and postpartum, a period when maternal calcium requirements are concurrently high. We found most pregnant and postpartum women taking thyroxine do not meet the recommended intake. As such, it is important that thyroxine labelling does not pose a barrier to adequate dietary calcium intake in this population.