ASSOCIATION OF METHOTREXATE (MTX), TNF-INHIBITORS (TNF-I) AND PREDNISONE (PRED) WITH RISK OF INFECTION AMONG RA PATIENTS

Background: Multiple studies have confirmed that the risk of infection is increased among RA patients. Although the role of TNF-I remains controversial, a number of studies have identified TNF-I use to be an independent risk factor. However, fewer studies have evaluated the risk of infection associated with MTX.Methods: We conducted a prospective cohort study using data from the CORRONA Registry. All patients with a diagnosis of RA by their treating MD and at least one follow-up visit were included. Variables with unadjusted associations in univariate analysis with either drug exposure or risk of infection were included in multivariate analyses. Person-years of drug exposure were calculated for the following categories: TNF-I drugs, MTX, PRED and other non-biologic DMARDs. Interactions between drugs were investigated. Finally, MTX and PRED exposure was also stratified by dose. Infections were reported during follow-up by MDs using standardized forms. Incident rate ratios (IRRs) were calculated from multiple variable GEE Poisson regression models adjusting for potential confounding variables including age, gender, race, comorbidities and RA disease activity and severity measures.Results: A total of 11,429 RA patients were followed for 15,901 patient years and 49,251 visits between Oct 2001 and Sept 2006. The cohort was 74.7% female; mean (SD) age was 59.0 (±13.6) years and 71.7% were RF positive. At enrollment, 61.3% were prescribed MTX, 34.7% TNF-I, 32.8% other non-biologic DMARDs and 38.5% prednisone. Significant predictors of infection in multivariate models included utilization of TNF-I, MTX and PRED, but not other DMARDs (See Table 1). There was a significant 2-way interaction between use of MTX and TNF. Combined use of MTX and TNF was associated with a lower risk than expected based on their individual risk contributions (p=0.002). No other drug interactions were observed. Other significant predictors included female gender, marital status, BMI, smoking history, diabetes, education, lung disease, tender joint count and functional class. Table 1 Drug Exposure Model Drug IRR (95% CI) P-value Model 1. Dichotomous Variables TNF-I 1.56 (1.34 - 1.83) <0.001 MTX 1.33 (1.15 - 1.54) <0.001 PRED 1.14 (1.04 - 1.25) 0.004 TNF x MTX Interaction – 0.002 Other DMARDs 1.06 (0.96 - 1.16) 0.251 Model 2. Dose Stratification TNF-I (all doses) 1.54 (1.31 - 1.80) <0.001 MTX 0 mg (none) 1.00 - MTX ≤ 12.5mg 1.37 (1.16 - 1.62) <0.001 MTX ≥ 15mg 1.33 (1.13 - 1.57) <0.001 PRED 0 mg (none) 1.00 - PRED 1 to 4 mg 1.11 (0.98 - 1.26) 0.102 PRED 5 to 9mg 1.03 (0.91 - 1.16) 0.645 PRED ≥ 10mg 1.51 (1.29 - 1.76) <0.001 TNF x MTX ≤ 12.5mg – 0.002 TNF x MTX ≥ 15mg – 0.023 Other DMARDS 1.04 (0.95 - 1.15) 0.407 Conclusion: These data confirm earlier observations of the association of both TNF-I and prednisone at doses > 10mg daily with risk of infection. These data indicate that MTX use is also an independent risk factor for infection. Interestingly, MTX use does not appear to further increase the risk associated with TNF-I use, based on evidence of a two-way interaction, when both are prescribed together. As MTX is presently widely prescribed in combination with biologic agents, these findings suggest that attribution of infectious causality should consider both categories of drugs.Citation: Ann Rheum Dis, volume 66, supplement II, year 2007, page 171Session: RA – anti-TNF therapy