Tapazole, PTU Hyperthyroid Drugs May Increase Birth Defect Risks: Study

New research suggests that side effects of Tapazole and PTU, two widely used hyperthyroid drugs, may cause serious birth defects when used during the early stages of pregnancy, including an increased risk of children being born with respiratory problems, neck defects and facial deformities.

In a study published last week in the Journal of Clinical Endocrinology and Metabolism, researchers evaluated Danish national data and found that the hyperthyroid medications may increase the risk of birth defects by 50 to 75%.

The two drugs analyzed were propylthiouracil (PTU) and methimazol (MMI), which is sold under the brand name Tapazole.

MMI is an oral contraceptive taken usually 3 times a day every 8 hours to prevent the thyroid gland from producing excess thyroid hormone, while PTU is an oral contraceptive taken typically every 8 hours by patients suffering from Graves’ disease, which is an autoimmune disease and one of the most common causes of hypothyroidism.

Both hyperthyroid drugs raised the risk of birth defects but resulted in different health problems for infants. The study indicated MMI use early on in pregnancy was associated with more musculoskeletal risks, abdominal wall defects, digestive problems, eye defects, and respiratory and circulatory defects. PTU was associated with more facial, neck, and urinary defects in infants when the mother took the medication in early stages of pregnancy.

The study involved a review of Danish national data including 849,416 births from 1996 to 2008, identifying cases where infants had a diagnosed birth defect before the age of 2 years old. From those cases of birth defects, 564 infants had been exposed to PTU, 1,097 were exposed to MMI, and 159 had been initially treated with MMI and then later switched to PTU.

After reviewing the results, MMI appeared to be the drug more prevalent in birth defect cases than PTU, averaging a 1.75 odds ratio versus PTU’s 1.5 ratio. Overall the researchers found the risk of birth defects was far more significant among newborns exposed to both drugs, with a 2 to 4 percent increase.

The research offers important contributions to the field, particularly with regard to the idea of sequential therapy, since there was no significant decreased risk in birth defects says Koenig.

Researchers have concluded that use of MMI and PTU in early stages of pregnancies to prevent hyperthyroidism may increase the rate of birth defects significantly, cautioning women taking medication for hyperthyroidism to be aware of signs of pregnancy and consult with their doctors to evaluate the best course of action.