[Bobbi]

#1019934

I saw this question asked in a thread, and decided to put it up as a topic for quicker reference.

As Ski mentioned PTU and methimazole do the same thing: they act as a chemical barrier to the production of thyroid hormone. They are different chemicals, which act in slightly different ways, but they have the same constellation of potential side effect issues.

So, why prescribe one over the other?

An added benefit of PTU is that it not only interferes with the production of thyroid hormone, but it also interferes with the conversion of T4 into T3 throughout the body. For someone who has excessively high levels of T3, PTU might be prescribed, therefore.

Another potential benefit of PTU is that is comes in a one-sized tablet (50 mg?) which can be combined to form much larger doses. I was on six PTU three times a day. As a result of taking multiple pills, it is possible to "fine-tune" our dose of PTU in ways that are not possible with methimazole. So, if a patient needs a "strange" level of ATD, PTU might provide more flexibility in dosage.

A drawback: PTU tastes terrible. Yes, indeed it does.

Another drawback to PTU: it has a pretty short "life-span" in the body, so you have to take it relatively evenly spaced, throughout the day. Timing the pills for every eight hours requires some diligence.

A benefit to methimazole is that it is only taken one time a day, typically. So if that dose works for you, you do not have pay attention multiple times a day to your dose needs. This is one reason why methimazole is more frequently prescribed for children. Getting a child to take one pill a day is significantly easier than expecting that child to take a foul-tasting pill at breakfast, lunch and dinner.

PTU and methimazole are both Class D drugs, meaning that they have the potential to harm a baby, in utero, or a breast-fed baby. PTU is known to cross the placental barrier (and also into breast milk) in smaller concentrations than does methimazole. So, PTU is recommended for mothers who are hyperthyroid. Whether it is "safe" for the baby depends upon the dose that the mother needs to keep her levels normal.

Bobbi — NGDF Online Facilitator

[Buttamama28]

#1075101

Thanks for the insight of the difference. I always wondered why my old endo put me on PTU. As for being pregnant, I was taking a pretty high dose so with my first child I didn’t start back taking it until I was about 6 1/2 months.I delivered him at 35wks @ 4lbs 15 ozs. It really was a pain because 2 wks after he was born I had to take him 70 miles from where I lived to the nearest children’s hospital because his levels were abnormal. So with my second child I took the risk of not taking it at all. And I had him at 38 1/2 wks @ 6lbs 9ozs. I don’t recommend that decision for everyone; but I really think doctors (endo) should be more specific with their patients. Especially those thinking about conceiving.

[Diane94]

#1075102

What is the difference between PTU and Methimazole? I’m on tapazole, what is that?

[LaurelM]

#1075103

Tapazole is a brand name of methimazole. I liked the convenience of the one a day pill (& no bad taste)of methimazole compared to the multiple dose of PTU with an icky taste.

Interestingly, the American Academy of Pedicatrics has a policy statement regarding the transfer of chemicals and drugs into human milk. They list both PTU and methimazole on the table for drugs usually compatable with breastfeeding. http://aappolicy.aappublications.org/cg … astfeeding

I think the caveat is ‘usually’. There are many factors in making that decision that should be discussed with both the mom & baby’s doctors. I was able to nurse our first while on methimazole. I was still on methimazole when we got pregnant with our second child (definately wanted but nature scheduled it earlier than we had). I was switched to PTU right away which I was on for only about 6 weeks into the pregnancy before I was completely taken off. I sometimes wonder if it was the second pregnancy that triggered the remission but I don’t really recommend it as a Grave’s ‘therapy’. I really would have been more comfortable being off medication for the entire pregnancy, especially in the first trimester when the baby’s thyroid is forming but you do what you need to do to at the time.

I think that Buttamama makes a good point that if you have a history of Grave’s and are considering conceiving, you should discuss the possible issues with your doctor.

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