SAN DIEGO – Blood levels of infliximab rose during pregnancy, while adalimumab levels remained stable, even after researchers accounted for changes in albumin, body mass index, and C-reactive protein levels, according to a novel single-center study of 25 women with inflammatory bowel disease (IBD).

Furthermore, blood levels of both anti–tumor necrosis factor agents varied considerably among patients, reported Dr. Cynthia Seow, a gastroenterologist at the University of Calgary (Alta.). “We should consider therapeutic drug monitoring during the prepregnancy period in order to optimize the dose during pregnancy,” she said. “Therapeutic drug monitoring may also be considered for pregnant women receiving infliximab in the second trimester to guide third-trimester dosing.

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Active IBD during pregnancy increases the risk of relapse and preterm birth, Dr. Seow noted at the annual Digestive Diseases Week. Thus, infliximab and adalimumab are used to keep IBD in check during pregnancy, even though they cross the placenta and reach higher levels in the cord blood and newborn (Clin Gastroenterol Hepatol. 2013 March;11[3]:286-92) than in the mother. “However, it is not known how pregnancy itself influences the pharmacokinetics of anti-TNF agents, or the implications of this on prescribed dosing,” said Dr. Seow.

Therefore, she and her colleagues analyzed blood samples from 25 women receiving stable maintenance anti-TNF therapy for IBD, who attended a median of three prenatal visits at the University of Calgary IBD Pregnancy Clinic. Fifteen women received infliximab during 15 pregnancies, and 10 women received adalimumab during 11 pregnancies. Infliximab levels were drawn at trough times, while adalimumab levels were usually drawn 3 days before the next injection. Blood samples were tested only after delivery, and anti-TNF doses were not adjusted during pregnancy.

The infliximab group included eight women with Crohn’s disease and seven women with ulcerative colitis, and the adalimumab group included nine women with Crohn’s disease and one with ulcerative colitis, said Dr. Seow. The treatment groups were similar in terms of age at diagnosis and pregnancy, time on anti-TNF agents, and average gestational age at delivery, which was 39.2 weeks (range, 38.1-40.2 weeks) for the infliximab group and 38.4 weeks (range, 37.2-39.6 weeks) for the adalimumab patients.

Median infliximab concentrations rose from 8.5 mcg/mL in the first trimester to a peak of 21 mcg/mL during the middle of the third trimester (P = .04), and then dropped to nearly preconception levels after delivery, Dr. Seow reported. “This change persisted irrespective of disease phenotype,” she added. Albumin levels correlated inversely with infliximab levels. In contrast, median adalimumab levels ranged between 8.6 and 12.2 mcg/mL during pregnancy, dropped to 6.8 mcg/mL after birth, and were unrelated to albumin levels.

Body mass index and C-reactive protein levels did not affect blood levels of either drug, and the researchers found no differences in pharmacokinetics in subgroups of patients who had only two blood draws, subtherapeutic drug levels, or consistently absent drug levels, Dr. Seow said. Three patients had detectable antibodies during pregnancy, all of whom had a stable clinical course, she said. “The antibody levels appeared to decrease as the pregnancy progressed, and then appeared to increase again after delivery.” A third of infliximab patients and nearly half of adalimumab patients were receiving combination treatments for IBD, and their anti-TNF blood levels resembled those of patients on monotherapy, she also noted.

The researchers did not test cord blood or blood sample from the newborns, but based on past evidence, fetal anti-TNF exposure has implications for current live vaccination recommendations in infants, Dr. Seow emphasized. “The long-term consequences of anti-TNF exposure remain unknown,” she concluded.

Dr. Seow disclosed ties with Janssen, AbbVie, Takeda, Shire, and Actavis.