Hypersensitivity to the active substance or to any of the excipients; During breast feeding; Severe hepatic impairment (serum bilirubin > 3.0 mg/dl); Jaundice; Severe bone marrow suppression and severe blood count alterations (leukocyte and/or platelet values dropped to < 3,000/µl or < 75,000/µl, respectively); Major surgery less than 30 days before start of treatment; Infections, especially involving leukocytopenia; Yellow fever vaccination.