[Cytopenia under topical imiquimod in two patients treated with oral hydroxyurea]

Aldara® is a topical immunomodulatory treatment. The risks of systemic passage are minimal. There have been rare reports of systemic adverse effects.

Case 1. Five sachets weekly of imiquimod were prescribed for Bowen's disease on the forearm in a patient known to have essential thrombocytosis under Hydrea®. His CBC was normal (6000 leukocytes/mm3, 2200 PMN/mm, 230,000 platelets/mm3). Imiquimod was given in 15 sachets weekly. Fifteen day later, the patient presented bicytopenia (3000 leukocytes/mm3, 1400 PMN/mm3, 119,000 platelets/mm3). Hydroxyurea and imiquimod were suspended until normalization of CBC. Hydroxyurea was resumed without recurrence of the bicytopenia. The patient's history included an identical episode following application of imiquimod. Case 2. Five sachets weekly of imiquimod were prescribed for actinic keratosis on the scalp in a patient known to have primary polycythemia under hydroxyurea. Her CBC was normal except for anemia (Hb 11.5g/L, 160,000 platelets/mm3, 1100 lymphocytes/mm3). Imiquimod was given in 12 sachets weekly. Ten days later, anemia increased (Hb 10g/dL) with lymphopenia (800/mm3) and thrombocytopenia (115,000/mm3). Suspension of imiquimod resulted in normalization of the previous CBC values.

. The literature review identified reports of dose-dependent lymphopenia under oral imiquimod but not under Aldara®. The National Pharmacovigilance Database listed 10 cases of hematological disorders most likely caused by Aldara®. Hydroxyurea may induce cytopenia, and while it was not considered the sole causative agent in this case, it is likely to have had a triggering role in these patients with blood dyscrasias. Our findings show that misuse of imiquimod carries a potential risk of hematologic abnormality in patients receiving concomitant hydroxyurea, a commonly combined drug.