Natalizumab therapy for moderate to severe Crohn disease in adolescents

Objectives: This study evaluated the safety, tolerability, and efficacy of natalizumab, a humanized monoclonal immunoglobulin-G4 antibody to alpha 4 integrin, in adolescent patients with moderately to severely active Crohn disease (CD). Patients and Methods: In a single-arm study, 38 adolescent patients (ages 12-17 y) with active CD (Pediatric Crohn Disease Activity Index [PCDAI] > 30) received 3 intravenous infusions of natalizumab (3 mg/kg) at 0, 4 and 8 weeks. The primary analysis was safety, assessed by adverse events, laboratory results, and vital signs. Pharmacokinetic and pharmacodynamic measurements and formation of anti-natalizumab antibodies also were analyzed. Efficacy outcomes were assessed by changes in PCDAI, quality of life (IMPACT III), and levels of C-reactive protein and serum albumin. Results: Thirty-one patients (82%) received 3 natalizumab infusions. The most common adverse events were headache (26%), pyrexia (21%) and CD exacerbation (24%). Clinical response (> 15-point decrease from baseline PCDAI) and remission (PCDAI <= 10) rates were greatest at week 10 (55% and 29%, respectively). Three patients (8%) tested positive for anti-natalizumab antibodies. The peak level (61.0 and 66.3 mu g/mL) and half-life (92.3 and 96.3 h) of natalizumab were comparable after the first and third infusions. Mean alpha 4 integrin receptor saturation was 93% at 2 hours and < 40% at 4 weeks after the first and third infusions. Increase from baseline in circulating lymphocytes ranged from 106% to 122% at 2 weeks and 45% to 65% at 4 weeks after each infusion. Conclusion: Natalizumab (3 mg/kg) was well tolerated in these adolescent patients with active CD, with a safety and efficacy profile similar to that of adult natalizumab-treated CD patients. Future studies should evaluate long-term safety and efficacy.