Objective: To examine the amount of improvement in renal survival that lupus patients require before choosing cyclophosphamide over azathioprine for the treatment of lupus nephritis.
Methods: Patients were presented with descriptions of cyclophosphamide and azathioprine and asked to indicate their preferred choice if each conferred an equal probability of renal survival. Strength of preference was assessed by systematically increasing the probability of renal survival of the more toxic treatment until the respondent's choice switched.
Results: Ninety-three well-educated women (mean age +/- SD 40 +/- 7 years) participated in the study. Ninety-eight percent (91/93) of the participants chose azathioprine over cyclophosphamide when both drugs conferred an equal probability of renal survival. Although most subjects switched preferences to cyclophosphamide for better renal survival, 31% (28/91) were unwilling to switch from azathioprine to cyclophosphamide for improved short-term renal survival, and 15% (14/91) were unwilling to switch from azathioprine to cyclophosphamide for improved long-term renal survival.
Conclusion: Although the majority of patients switched preferences to cyclophosphamide for better renal survival, a substantial minority was unwilling to accept the toxicity associated with cyclophosphamide, even if it was much better than azathioprine at preventing renal failure.