Efficacy, Pharmacokinetic, and Safety Assessment of Adalimumab, a Fully Human Anti-tumor Necrosis Factor-alpha Monoclonal Antibody, in Adults with Rheumatoid Arthritis Receiving Concomitant Methotrexate: a Pilot Study

Background: Because traditional therapies for rheumatoid arthritis (RA) such as methotrexate (MTX) do not produce an adequate response in many patients, newer therapies that block the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) are increasingly being used in combination with MTX.

Objective: This study evaluated the efficacy, pharmacokinetics, and safety profile of adalimumab, a fully human anti-TNF alpha monoclonal antibody, when added to continuing MTX therapy.

Methods: This Phase I, randomized, dose-titration study consisted of a 4-week, double-blind, placebo-controlled treatment phase and a 26-month, open-label continuation phase. Patients with RA who had been taking stable doses of MTX (mean dose, 17 mg/wk) for > or =3 months before enrollment with an inadequate response were randomly assigned to receive 2 single doses of either adalimumab 0.25, 0.5, 1, 3, or 5 mg/kg i.v. or placebo in the double-blind phase. In the open-label phase, patients received treatment with 1 of the doses of adalimumab every other week or monthly for 18 months; patients were then switched to adalimumab 40 mg i.v. or SC every other week or monthly. The main efficacy end point was 20% improvement in American College of Rheumatology response criteria (ACR20). Other efficacy end points included 50% (ACR50) and 70% improvements in ACR response criteria. Pharmacokinetic parameters were analyzed for adalimumab and MTX during both phases of the study. Serum adalimumab concentrations were analyzed using a validated enzyme-linked immunosorbent assay relying on the double-antigen principle. Peak and trough concentrations were determined from observed concentration-time data, and a modeling approach was used to estimate total serum clearance, mean apparent terminal half-life, apparent volume of distribution at steady state, and area under the concentration-time curve.

Results: Sixty patients entered the double-blind phase, 45 receiving adalimumab and 15 receiving placebo; 1 placebo recipient chose not to continue into the open-label phase. Overall, the study population included 47 (78.3%) women and 13 (21.7%) men. The mean age was 52.9 years (range, 24-73 years), and the mean body weight was 69.7 kg (range, 43-98 kg). ACR20 and ACR50 responses were achieved on at least 1 assessment during the 4-week double-blind phase by a respective 29 (64.4%) and 11 (24.4%) of 45 patients receiving active treatment and by 4 (26.7%) and none of the 15 patients receiving placebo. Responses to adalimumab were rapid, with 10 (22.2%) of 45 patients achieving an ACR20 response within 24 hours of dosing. Of 29 adalimumab recipients who had an ACR20 response, 18 (62.1%) had a duration of response (time from first occurrence of a response to first occurrence of a nonresponse) of 1 to 2 weeks, and 11 (37.9%) had a duration of response of 3 to 13 weeks. The pharmacokinetic properties of adalimumab appeared to be linear. The mean apparent terminal half-life after a single intravenous dose of adalimumab ranged from 15 to 19 days in the 5 dose groups. Repeated administration of adalimumab had no statistically significant effect on the pharmacokinetics of MTX, indicating that dose adjustment of MTX is not necessary. Adalimumab was well tolerated, and there were no dose-related adverse events.

Conclusions: Among patients with active RA who had not had an adequate response to MTX, addition of adalimumab to MTX achieved statistically significant, long-term improvement compared with placebo plus MTX (P < or = 0.05), as indicated by ACR responses at 26 months. The combination was well tolerated. Adalimumab exhibited linear pharmacokinetics. In this selected patient population, adalimumab's long half-life of 15 to 19 days supports every-other-week dosing. Coadministration of adalimumab did not alter serum levels of MTX.