Primary mammary actinomycosis challenged with penicillin allergy.

Actinomycosis is a subacute-to-chronic bacterial infection caused by gram-positive, filamentous, non-acid-fast, facultative anaerobic bacteria. It is a normal commensal bacterium found in the oral cavity and the lower reproductive tract of women. We present a case of primary actinomycosis of the breast. A postmenopausal woman, complicated by penicillin allergy, presented with a left breast lump clinically simulating malignancy. The first line of treatment for actinomycosis is penicillin. Due to a penicillin allergy, the patient was initially treated with doxycycline. However, doxycycline was discontinued due to tremors, and was replaced by clindamycin. The patient had a good clinical response with resolution of the abscess.