Herpes virus infections occur frequently following treatment with fludarabine: results of a prospective natural history study

We performed a prospective infectious natural history study of 21 patients with low‐grade lymphoproliferative disorders receiving fludarabine as initial (n = 5) or salvage (n = 16) therapy. 12 (57%) of these patients developed herpes zoster (n = 9), herpes simplex I (n = 1) or herpes simplex II (n = 2) infections at a median of 8 (range 1–17) months following initiation of fludarabine, with 75% of these having completed therapy. All patients with herpes zoster developed severe post‐herpetic neuralgia. Factors differentiating patients developing these infections included older age and low serum IgG or IgA. Based upon these prospective data, we conclude that herpes virus infections frequently occur following fludarabine treatment, necessitating aggressive patient education and new prophylactic strategies.