Elizabeth,
Budesonide has been available for use in inhalers to treat asthma and similar issues, for a number of years, so more research data were available early on, for that particular use. But it's not the same as oral use. From the quote above, this phrase is probably why the manufacturer is reluctant to recommend oral budesonide:
a 9 mg daily dose (in both single and repeated dose pharmacokinetic studies) of oral budesonide is approximately 10 times higher than that for a 800 microgram daily dose of inhaled budesonide.
IOW, this suggests that 3 mg per day (one capsule per day), or every other day, for example, might not be a significant risk, but a full dose of 3 capsules per day might expose a nursing baby to a measurable amount of risk. It's difficult to say, since not enough research has been done to provide any truly conclusive results.
Controlling your symptoms may be difficult for a while, because certain hormones remain very elevated during lactation. I can't advise you to try this, since I'm not a doctor, but to me, an MC flare due to hormones suggests a possible mast cell issue. Quite a few members here have found that one or more antihistamines seem to work just as well for them as Entocort. Have you ever tried using an antihistamine for controlling your MC symptoms?
Your doctors aren't likely to know anything about using antihistamines to treat MC, but if you are considering taking a corticosteroid while nursing the baby, it would probably be a good idea to discuss that with both your GI specialist and the baby's pediatrician. It is known, for example, (at least it's been shown by research), that waiting approximately 4 hours after taking a dose of prednisone, before allowing a baby to nurse, can reduce the amount of prednosolone (the active ingredient in prednisone) that's transmitted to the baby, to only a relatively small fraction of the amount that would be transmitted if the baby were allowed to nurse within, say, the first hour after taking the prednisone.
Here's some more info on the use of prednisone:
Prednisone Breastfeeding Warnings
In one study of six lactating women, prednisolone milk concentrations were 5% to 25% of corresponding serum concentrations. The authors estimated that a nursing infant would be exposed to negligible amounts of drug with maternal doses of 20 to 40 mg per day. The excretion of prednisolone into breast milk has been evaluated in six women on chronic prednisolone therapy. Milk prednisolone concentrations ranged from less than 10 to 106 ng/mL in patients receiving 10 mg to 45 mg per day (N=5). In a patient receiving 80 mg per day, milk prednisolone concentrations ranged from less than 10 ng/mL prior to the morning dose to 317 ng/mL at one hour post-dose. The peak milk to plasma concentration ratio ranged from 0.12 to 0.25. The authors recommend that nursing be withheld for four hours after administration of doses greater than 20 mg. In a recent study, prednisolone excretion into breast milk was evaluated in three women following administration of prednisolone phosphate 50 mg intravenously one time. During the six-hour study period, 0.010% to 0.049% of the administered dose of prednisolone was recovered in breast milk. Nursing infants would be expected to experience minimal exposure. Data from this study also suggest that exchange of unbound prednisolone between breast milk and serum is rapid and bi-directional.
Prednisone and its active metabolite prednisolone are excreted into human milk in small amounts. Animal studies have revealed an increased incidence of cleft palate in offspring. In one study of six lactating women, prednisolone milk concentrations were 5% to 25% of corresponding serum concentrations. The authors estimated that a nursing infant would be exposed to negligible amounts of drug with maternal doses of 20 to 40 mg per day. The excretion of prednisolone into breast milk has been evaluated in six women on chronic prednisolone therapy. Milk prednisolone concentrations ranged from less than 10 to 106 ng/mL in patients receiving 10 mg to 45 mg per day (N=5). In a patient receiving 80 mg per day, milk prednisolone concentrations ranged from less than 10 ng/mL prior to the morning dose to 317 ng/mL at one hour post-dose. The peak milk to plasma concentration ratio ranged from 0.12 to 0.25. The authors recommend that nursing be withheld for four hours after administration of doses greater than 20 mg. In a recent study, prednisolone excretion into breast milk was evaluated in three women following administration of prednisolone phosphate 50 mg intravenously one time. During the six-hour study period, 0.010% to 0.049% of the administered dose of prednisolone was recovered in breast milk. Nursing infants would be expected to experience minimal exposure. Data from this study also suggest that exchange of unbound prednisolone between breast milk and serum is rapid and bi-directional. Prednisone is considered compatible with breast-feeding by the American Academy of Pediatrics. The manufacturer recommends that caution be used when administering prednisone to nursing women.
http://www.drugs.com/pregnancy/prednisone.html
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including all those hormonal changes that occur following delivery 