PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior immunotherapy Chemotherapy: At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas) Endocrine therapy: At least 4 weeks since prior anticancer hormonal therapy Radiotherapy: At least 4 weeks since prior radiotherapy (6 weeks for extensive radiotherapy) No concurrent radiotherapy except for localized palliation Surgery: Not specified Other: No other concurrent investigational drugs or antitumor drugs No sulphonylureas or anti-arrhythmic agents