DISEASE CHARACTERISTICS:

• Diagnosis of multiple myeloma meeting at least 1 of the following criteria:
• Relapsed disease after a response to standard first-line chemotherapy (e.g., vincristine, doxorubicin, and dexamethasone [VAD] OR melphalan and prednisone) or first-line high-dose chemotherapy
• Refractory disease (failed to achieve at least stable disease) to most recent chemotherapy with or without systemic corticosteroids
• Measurable disease, defined as a monoclonal immunoglobulin spike on serum electrophoresis of ≥ 1 g/dL AND/OR urine monoclonal immunoglobulin spike of ≥ 200 mg/24 hours
• No non-secretory myeloma
• No plasma cell leukemia

PATIENT CHARACTERISTICS:

Age

• 18 and over

Performance status

• Karnofsky 60-100%

Life expectancy

• More than 3 months

Hematopoietic

• Platelet count ≥ 50,000/mm^3 (30,000/mm^3 if bone marrow is extensively infiltrated)
• Hemoglobin ≥ 8.0 g/dL
• Absolute neutrophil count ≥ 1,000/mm^3
• Pancytopenia secondary to multiple myeloma or hypersplenism allowed

Hepatic

• AST and ALT ≤ 3 times upper limit of normal (ULN)
• Bilirubin ≤ 2 times ULN (unless clearly related to disease)
• No known active hepatitis B or C infection

Renal

• Calcium < 14 mg/dL

Cardiovascular

• No evidence of acute ischemia or new conduction system abnormality by electrocardiogram
• No myocardial infarction within the past 6 months
• No New York Heart Association class III or IV heart failure
• No poorly controlled hypertension
• No prolonged corrected QT interval (> 460 ms) with potassium > 4 mmol/L and magnesium ≥ 1.8 mmol/L

Other

• No active infection
• No POEMS syndrome (plasma cell dyscrasia with polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes)
• No diabetes mellitus
• No other serious medical or psychiatric illness that would preclude study participation
• No known allergic reaction attributable to compounds of similar chemical or biological composition to study drugs
• No history of grand mal seizures
• HIV negative
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy

• More than 4 weeks since prior immunotherapy or antibody therapy

Chemotherapy

• See Disease Characteristics
• More than 3 weeks since prior chemotherapy (6 weeks for nitrosoureas)

Endocrine therapy

• See Disease Characteristics
• No other concurrent corticosteroids

Radiotherapy

• More than 4 weeks since prior radiotherapy

Surgery

• More than 4 weeks since prior major surgery

Other

• No other concurrent investigational agents