Exposure to thiopurine drugs through breast milk is low based on metabolite concentrations in mother-infant pairs.
OBJECTIVE
To determine infant exposure to 6-thioguanine and 6-methylmercaptopurine nucleotides (6-TGN and 6-MMPN, respectively) during maternal use of azathioprine in breastfeeding.


METHODS
Mother-infant pairs provided blood for determination of 6-TGN and 6-MMPN concentrations, and TPMT genotype.


RESULTS
Four women taking azathioprine 1.2-2.1 mg kg(-1) day(-1) and their infants were studied. All had the wild-type TPMT genotype. Maternal 6-TGN and 6-MMPN concentrations ranged from 234 to 291 and 284 to 1178 pmol per 8 x 10(8) red blood cells, respectively, and were consistent with those associated with improved therapeutic outcomes. Neither 6-TGN nor 6-MMPN was detected in any of the infants, despite a sensitive assay.


CONCLUSIONS
The data suggest that azathioprine may be 'safe' during breastfeeding in patients with the wild-type TPMT genotype ( approximately 90% of caucasian patients) taking 'normal' doses.
Gardiner
Sharon J
SJ
Department of Clinical Pharmacology, Christchurch Hospital and Christchurch School of Medicine, Christchurch, New Zealand. sharon.gardiner@cdhb.govt.nz
Gearry
Richard B
RB
Roberts
Rebecca L
RL
Zhang
Mei
M
Barclay
Murray L
ML
Begg
Evan J
EJ
D000328:Adult; D001379:Azathioprine / Q000009:adverse effects* / Q000378:metabolism; D001942:Breast Feeding / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000009:adverse effects / Q000627:therapeutic use*; D007223:Infant; D008297:Male; D015122:Mercaptopurine / Q000031:analogs & derivatives / Q000097:blood; D008780:Methyltransferases / Q000235:genetics*; D009035:Mothers; D013866:Thioguanine / Q000097:blood
D007166:Immunosuppressive Agents; C010240:6-methylthiopurine; D015122:Mercaptopurine; D008780:Methyltransferases; D013866:Thioguanine; D001379:Azathioprine