Associations between toxicity and individual level factors.

Note: Age was centered; and missing values for BMI, clinical stage, and CD4 cell counts were included as a separate category. Adjusted incidence rate ratios [aIRR] of all-cause toxicity for the interaction between duration of exposure and stavudine dosage were 1.28 (95% CI 1.10–1.49), 0.66 (95% CI 0.49–0.89), and 0.69 (95% CI 0.32–1.51) for the second, third, and fourth years of exposure to stavudine 40 mg, respectively, compared to the first year of stavudine 30 mg. The corresponding aIRR of specific toxicity were 1.14 (95% CI 0.97–1.34), 0.56 (95% CI 0.40–0.79), and 0.47 (95% CI 0.17–1.29), respectively. P value from likelihood rate ratio tests for association were calculated across all categories of a given variable.