Low dose of infliximab is inadequate in most patients with spondylarthropathies.

OBJECTIVES

The recommended starting dose for infliximab for ankylosing spondylitis 5mg/kg is higher than that for rheumatoid arthritis. Because of the high expense of the drug lower doses may be considered. We report our experience with lower initial doses.

METHODS

Thirty patients with active SpA (16 psoriatic arthritis, 12 ankylosing spondylitis and 2 undifferentiated) received 6 infliximab infusions. Patients had substantial axial disease (mean BASDAI at baseline 5.5). Concomitant therapy (methotrexate or prednisolone) remained stable throughout treatment period. The mean initial dose of infliximab was 3.5 mg/kg/infusion. Clinical efficacy was assessed by BASDAI. The criterion for dose adjustment was a BASDAI improvement of less than 50%. The primary end-points were the proportion of patients requiring a dose adjustment and the percentage of patients achieving 50% improvement in BASDAI after 6 infusions.

RESULTS

In this cohort, 2 patients discontinued therapy, 1 for pulmonary infection and 1 for allergic reaction. Twelve patients (40%) showed 50% improvement in BASDAI between baseline and prior to the 7th infusion, while 15 patients (50%) had an improvement > 2 points. To achieve clinical response the frequency and/or the dose of infliximab infusions were increased in 63% of patients. The mean infliximab dose increased from 3.5 mg/kg at the first infusion to 4.3 mg/kg (p < 0.001) at the 7th infusion, resulting in a cumulative dose at the end of the study period comparable to the recommended one.

CONCLUSIONS

In the majority of our SpA patients low starting doses of infliximab required subsequent adjustment. In these patients infliximab should be administered at the recommended dose of 5mg/kg/infusion.