Can monthly Cosentyx (secukinumab) injections cause the observed drop in white blood cell count and neutrophil count?

Can Cosentyx Cause Neutropenia and Leukopenia?

Yes, Cosentyx (secukinumab) can cause neutropenia, though most cases are mild, transient, and reversible. 1

Evidence from Drug Labeling and Guidelines

The prescribing information for Cosentyx acknowledges that neutropenia has been reported with secukinumab treatment 1. Specifically:

• Most cases of neutropenia are mild, transient, and reversible
• Rare cases of Grade 4 neutropenia (CTCAE) have been documented 1
• The drug label does not list routine white blood cell monitoring as a requirement for secukinumab therapy 2

This contrasts sharply with medications like clozapine, which requires extensive WBC monitoring protocols due to ~1% risk of agranulocytosis 3.

Clinical Context and Mechanism

Secukinumab's mechanism may actually reduce certain inflammatory markers rather than suppress bone marrow function:

• Treatment with secukinumab reduces neutrophil counts and leukocyte counts as part of its anti-inflammatory effect 4
• Studies show neutrophil count and leukocyte count significantly decreased after secukinumab treatment (P < .001), but this appears to reflect reduced systemic inflammation rather than bone marrow suppression 4
• The drug reduces epidermal neutrophils in psoriatic plaques as part of its therapeutic mechanism 2

Differentiating Drug Effect from Other Causes

Important considerations when evaluating low WBC/neutrophils in a patient on Cosentyx:

1. Timing matters: If the drop occurred shortly after starting or increasing corticosteroids (which patients with inflammatory conditions often receive), consider steroid-induced redistribution rather than Cosentyx toxicity 5

2. Severity assessment:

   • Mild, transient decreases are consistent with Cosentyx's known profile 1
   • Severe neutropenia (ANC <500/mm³) or Grade 4 neutropenia would be unusual and warrant investigation for other causes 1

3. Other medications: Review for concurrent drugs that can lower blood counts (e.g., carbamazepine, other immunosuppressants) 3

4. Infection workup: Rule out viral infections (CMV, EBV, parvovirus) that can cause cytopenias 6, 7

Management Approach

For mild to moderate neutropenia in a patient on Cosentyx:

• Continue monitoring with serial CBCs to assess trajectory
• Most cases resolve spontaneously without intervention 1
• Consider holding Cosentyx temporarily if neutropenia is moderate (ANC 500-1000/mm³) and monitor for recovery
• Permanently discontinue only if severe (Grade 4) neutropenia develops or if associated with serious infection 1

This differs from the aggressive monitoring and discontinuation protocols required for drugs with known marrow toxicity (like clozapine requiring immediate cessation if WBC <2000/mm³ or ANC <1000/mm³) 3.

Key Clinical Pitfall

Do not confuse the expected anti-inflammatory reduction in neutrophils with pathologic bone marrow suppression. Research demonstrates that secukinumab reduces inflammatory markers including neutrophil counts as part of its therapeutic effect 4, 8, which is fundamentally different from drugs causing agranulocytosis or aplastic anemia.

If the WBC/neutrophil drop is mild and the patient is clinically well without signs of infection, this likely represents the drug's anti-inflammatory effect rather than a serious adverse event requiring discontinuation.