Can Plaquenil (Hydroxychloroquine) Cause Low WBC?
Yes, hydroxychloroquine can cause leukopenia (low white blood cell count), and this is a recognized hematologic toxicity that requires periodic monitoring, particularly in patients on prolonged therapy. 1
Mechanism and FDA Recognition
The FDA label explicitly states that hydroxychloroquine may cause myelosuppression including leukopenia, agranulocytosis, aplastic anemia, and thrombocytopenia. 1 This is a direct bone marrow suppressive effect that can affect multiple cell lines, not just white blood cells. 1
Monitoring Requirements
Blood cell counts should be monitored periodically in patients on prolonged hydroxychloroquine therapy. 1 The FDA recommends that if a patient develops myelosuppression that cannot be attributed to the underlying disease being treated, the drug should be discontinued. 1
Risk Factors and Clinical Context
Dose-dependent risk: Higher doses carry greater risk of hematologic toxicity, particularly when combined with other medications that may cause anemia or cytopenias. 2
Additive effects: Patients taking concomitant medications that affect blood cell counts may experience additive hematologic toxicity and require more careful monitoring. 2
Renal impairment: Patients with reduced kidney function may be at higher risk due to decreased drug clearance, though the strength of this evidence is limited. 2
Clinical Pitfalls to Avoid
A common mistake is attributing leukopenia solely to the underlying autoimmune disease (such as lupus or rheumatoid arthritis) without considering hydroxychloroquine as a contributing factor. 1 The FDA specifically notes that if myelosuppression cannot be attributed to the disease itself, the drug should be discontinued. 1
Another pitfall is failing to establish baseline blood counts before initiating therapy, which makes it difficult to determine whether subsequent cytopenias are drug-related or disease-related. 2
When to Discontinue
Discontinue hydroxychloroquine if the patient develops myelosuppression that cannot be attributed to the underlying disease. 1 This requires clinical judgment to distinguish between disease activity and drug toxicity, but when in doubt, drug discontinuation should be strongly considered given the potential for progression to more severe cytopenias including agranulocytosis. 1