To determine the reasons for changing treatment from mycophenolate mofetil (MMF) to azathioprine (AZA) or vice versa in lupus patients and to evaluate the effect of the change.
Lupus patients were identified from the University of Toronto Lupus Clinic database. Global disease activity in the 6 months prior to the change in therapy and 6 months after the change was calculated. The reasons for changing therapy were identified.
One hundred eight switches occurred among 92 lupus patients: 89 switches from AZA to MMF and 19 from MMF to AZA. There was significant improvement in disease activity in the 6 months after drug switching compared to the 6 months prior to the switch when the reason was a drug failure. There was no statistically significant deterioration in disease activity in the 6 months after drug switching when the reason for the switch was a side effect, pregnancy, renal transplant, or financial. In the 19 patients who switched because of side effects, 15 (79%) had resolution of the side effects.
Switching from AZA to MMF is most often due to AZA failure, whereas switching from MMF to AZA is mostly due to side effects and pregnancy. When the reason for the switch was drug failure, improvement in disease activity occurred and there was a reduction of steroid dose after 6 months. When the reason for switching was something other than drug failure, there was no deterioration in global disease activity. Switching for side effects usually resulted in elimination of the side effect.