• Paula E Keating, Barry D Hock, Stewart M Smith, ChinPaul K LPKL0000-0002-5470-5191Department of Medicine, University of Otago, Christchurch, New Zealand.Department of Clinical Pharmacology, Christchurch Hospital, Christchurch, New Zealand., John L O'Donnell, and Murray L Barclay.
• Immunology Section, Canterbury Health Laboratories, Christchurch, New Zealand.
• Intern Med J. 2023 Nov 1; 53 (11): 212321272123-2127.

AbstractA review of laboratory results across New Zealand for therapeutic drug monitoring (TDM) of infliximab and adalimumab concentrations and antidrug antibodies (ADAs) over 4 years was completed. Of 6591 results, the median serum concentration for infliximab was 5.7 mg/L and for adalimumab was 5.5 mg/L. Subtherapeutic drug concentrations (<7 mg/L) were measured in 54% of samples. Drug concentrations <2 mg/L were measured in 23% of samples, with ADAs detected in 51% of these. The high number of samples with subtherapeutic drug concentrations and common ADA detection is consistent with failing therapy but could also suggest that standard dosing is frequently too low for patients. These results reinforce the value of antitumour necrosis factor drug TDM in making decisions to adjust dosing or switch agents in patients taking infliximab and adalimumab.© 2023 Royal Australasian College of Physicians.

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