Biologic Therapy Treatment Complications in
the Alberta Aboriginal Population with Rheumatoid Arthritis

Background/Purpose: Aboriginal people with rheumatoid
arthritis (RA) have more severe disease and an increased number of comorbid
conditions, which may result in higher rates of adverse events when using
biologic therapy.

Methods: The Alberta Biologics Pharmacosurveillance Program (ABioPharm)
is a longitudinal RA cohort study, linked to population-based administrative
databases (physician claims and hospitalizations). We calculated incidence rate
ratios (IRR) for adverse events comparing Aboriginal to non-Aboriginal groups,
including all-cause hospitalization, serious infections, malignancy (lung,
breast, colorectal, lymphoproliferative), cardiovascular events (myocardial
infarction, congestive heart failure, cerebrovascular disease), thromboembolic
events and death, using Poisson regression to adjust for age at biologic start,
low socioeconomic status, urban vs rural residence, comorbidities (Deyo-Charlson), number of rheumatologist visits, history of
joint replacement surgery, extra-articular features, baseline DAS28, baseline
HAQ, number of previous DMARDs, steroids at baseline visit, and standardized
for age and sex.

Results: The cohort includes 1,545 patients
(n=83 Aboriginal) with a total of 8,145 person-years of follow-up. Aboriginals
were younger at initiation of the first biologic (50 vs 55 years), with more
comorbidities, higher baseline DAS28ESR scores (mean 6.11 vs 5.19) and slower
rates of improvement for tender and swollen joint counts in the first year of
treatment. Aboriginals had a higher risk of all-cause hospitalization (IRR 1.4,
95%CI 1.1 to 1.8, p=0.01), malignancy (IRR 2.6, 95%CI 1.1 to 5.7, p=0.02) and
thromboembolic events (IRR 2.7, 95%CI 1.7 to 4.2, p<0.001). They also had
higher risk of serious infections (IRR 3.2, 95%CI 2.5 to 4.0, p<0.001), with
significantly more episodes of skin and soft tissue infections (IRR 3.8, 95%CI
1.5 to 9.6), osteomyelitis (IRR 6.6, 95%CI 1.8 to 25.1) and pyelonephritis (IRR
8.4, 95%CI 2.0 to 35.3). Aboriginal patients were similar to non-Aboriginal
patients in the risk for cardiovascular events (IRR 0.7, 95%CI 0.5 to 1.1,
p=0.03). The mortality rate was 0.7 per 100 person-years in the non-Aboriginal
group, with no deaths in the Aboriginal group.

Conclusion: Aboriginal patients experience
higher rates of all-cause hospitalization, serious infections, malignancy and
thromboembolic events, but not cardiovascular events, during treatment with
biologic therapy. These findings are important to inform treatment decisions to
initiate biologic therapy in Aboriginal patients, and the need for frequent
monitoring during therapy.