Differential Rates of Toxicity Between Chloroquine and Hydroxychloroquine

Purpose: To describe two cases of patients with systemic lupus erythematosus (SLE) who manifested differential rates of retinal toxicity progression on hydroxychloroquine (HCQ) and chloroquine (CQ), respectively. Methods: Retrospective case reports. Results: Case 1 is a 41-year-old woman with SLE and history of renal involvement, who had been managed on HCQ for 14 years and gradually progressed to moderate retinal toxicity over several years. Case 2 is a 59-year-old woman with SLE and history of renal involvement, who had been managed on quinacrine for 20 years followed by chloroquine for 5 years and initially presented without any evidence of retinal toxicity. One year later, she manifested moderate retinal toxicity. Both cases were screened regularly. In case 1, the diagnosis was missed and toxicity progressed predictably and slowly while on HQ. In case 2, there was no salient pathology on OCT or HVF testing at initial presentation. One year later, there was moderate toxicity. Conclusion: Given the dramatically different rate of progression of retinal toxicity in these two patients, these cases highlight potential gaps in our understanding of retinal toxicity and provide rationale to potentially study rates of retinal toxicity progression in patients on CQ or quinacrine.