Carbimazole instead of Methimazole and PTU while breastfeeding

[bertrande]

Hi, I was recently diagnosed with Graves and am 4.5 months postpartum. The endocrinologist, mindful that I am breastfeeding, prescribed carbimazole 10mg a day and propranolol 10mg 2-4x a day (depending on how I feel). I am currently taking propranolol twice a day but do feel lightheaded and queasy after each dose. The endo did not specify whether the carbimazole med should be taken once a day or in divided doses - will it make a difference to the levels secreted in the breast milk if I don't take it in a divided dose considering the total level secreted per day in the breastmilk should remain the same? I tried asking for Methimazole as I understand it is currently the medicine of choice but my endo said carbimazole is the same as methimazole and should be ok. Is this accurate?

Also, would you recommend pumping and dumping my milk after taking the carbimazole? The endo did not think it would matter but I am just wondering if I should err on the side of caution.

Thank you very much in advance.

[admin]

Bertrande:

Methimazole is metabolized to the active drug, carbimazole. Thus there is really no difference between these two drugs. We have two studies of carbimazole at 30 and 40 mg/day doses.

Plasma levels in infants in both studies were subclinical at these doses, that are actually higher than yours. NO thyroid suppression was found in the infants which is good news.

Still it would be a good idea to have your infants' thyroid checked periodically. Talk with your pediatrician about this.

Lastly, propranolol is generally only used initially during the period of "high" thyroid levels, sometimes call the "thyroid storm". It is seldom used when thyroid levels are brought under control with the methimazole or carbimazole. I'd talk with your physician to see if you really need to take it.


Tom Hale R.Ph., Ph.d.

[bertrande]

Dear Dr Hale,

Thanks for the response - I will tee up with my paediatrician. Today is only my second day on Carbimazole and the specialist reckoned I needed propranolol for a few more days yet. Do we know the half life of carbimazole? I take it immediately after I express my milk but wonder if I should then wait a few hours before the next expression session.

Best regards
Bertrande

[Sandra]

Carbimazole peaks at 2-4 hours and has a half-life of 6-13 hours, taking right after expressing or breastfeeding is best where you have a little break period before feeding again.

Sandra Lovato R.N.
InfantRisk Center
806-352-2519

[Nic]

Hi there

i have been diagnosed with hyperthyroidism. My levels are t4 75.6 tsh 0.01 t3 26.5.

my doctor has advised me to stop breastfeeding and take 30mg a day a day of carbimazole. My wee boy is 4 months old and exclusively breastfed and thriving.

what is your opinion on continuing breastfeeding my son?

Many thanks

[admin]

Nic,

Carbimazole, a prodrug of methimazole, is completely converted to the active metabolite methimazole in the plasma. Carbimazole is rated an L3-limited data-probably compatible. The amount that transfers into breast milk is 2.3-5.3% of your dose. Milk levels of methimazole depend on maternal dose but appear too low to produce clinical effects in the infant. It is probably ok to breastfeed if you have your infants thyroid functions monitored during your therapy.

Sandra Lovato R.N.
InfantRisk Center
806-352-2519