Simponi is golimumab, a monoclonal antibody. Monoclonal antibodies tend to be rather large. They are fragile proteins which are destroyed in the stomach if ingested orally, so they must be administered via injection. 

While only Dr. Hale and his people are likely to have any specific case reports on the safety of Simponi in breastfeeding, there is a fair amount of data, some published and some not published, regarding the safe use of a number of other monoclonal antibodies in breastfeeding. 

I am extra familiar with this topic because I am a pharmacist who has taken several of these medications while breastfeeding (Remicade, Humira, Anakinra), with no adverse events. The first one I took was Remicade (infliximab) and I was part of a study which 4 years later has not been published, which consisted of about 15 breastfeeding dyads. Samples were taken of Mom's blood, milk, and baby's blood. No Remicade was found in the milk or in the babies blood samples, which was exactly what we expected to happen. 

Interestingly, a study published about a year ago (citation below) suggested that breastfeeding in another auto-immune disease, Multiple Sclerosis, helped to keep a lid on the disease. There is a line of thinking that breastfeeding could help ease a number of autoimmune conditions, but this warrants further study (and probably wants for funding). 

Be well, 
Laura C. Block, PharmD

Exclusive breastfeeding and the risk of postpartum relapses in women with multiple sclerosis.
Langer-Gould A, Huang SM, Gupta R, Leimpeter AD, Greenwood E, Albers KB, Van Den Eeden SK, Nelson LM.
Arch Neurol. 2009 Aug;66(8):958-63. Epub 2009 Jun 8.

*****
Date:    Wed, 29 Sep 2010 09:49:57 -0500
From:    [log in to unmask]
Subject: Re: Rheumatoid arthritis and Enbrel use
Enbrel has a huge molecular weight, is not orally given.  Although not reviewed, it should be safe for breastfeeding mothers.  See Thomas Hale.  But logically, if the mother can't use the drug unless given parenterally, not orally, even if it DID enter the milk, how could it be absorbed by the baby?
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